From 752a06ec0ebf20d6232b13f1ea53fe21fefcefbd Mon Sep 17 00:00:00 2001 From: Sadeep Madurange Date: Mon, 8 Dec 2025 17:34:35 +0800 Subject: Fix list indentation. --- _archive/arduino-due.md | 122 --------- _archive/arduino-due/connections.jpeg | Bin 29090 -> 0 bytes _archive/arduino-due/schematic.png | Bin 68688 -> 0 bytes _archive/arduino-due/source.tar.gz | Bin 1174 -> 0 bytes _archive/arduino-uno.md | 82 ------ _archive/arduino-uno/3v3.Makefile | 46 ---- _archive/arduino-uno/Makefile | 43 --- _archive/arduino-uno/breadboard.jpeg | Bin 54319 -> 0 bytes _archive/arduino-uno/pinout.png | Bin 247197 -> 0 bytes _archive/mosfet-switches.md | 123 --------- _archive/mosfet-switches/bjt.png | Bin 12838 -> 0 bytes _archive/mosfet-switches/n_high_side.png | Bin 10825 -> 0 bytes _archive/mosfet-switches/p_high_side.png | Bin 10724 -> 0 bytes _archive/neo4j-a-star-search.md | 318 ---------------------- _archive/suckless-software.md | 90 ------- _blog/arduino-due.md | 122 +++++++++ _blog/arduino-due/connections.jpeg | Bin 0 -> 29090 bytes _blog/arduino-due/schematic.png | Bin 0 -> 68688 bytes _blog/arduino-due/source.tar.gz | Bin 0 -> 1174 bytes _blog/arduino-uno.md | 82 ++++++ _blog/arduino-uno/3v3.Makefile | 46 ++++ _blog/arduino-uno/Makefile | 43 +++ _blog/arduino-uno/breadboard.jpeg | Bin 0 -> 54319 bytes _blog/arduino-uno/pinout.png | Bin 0 -> 247197 bytes _blog/mosfet-switches.md | 123 +++++++++ _blog/mosfet-switches/bjt.png | Bin 0 -> 12838 bytes _blog/mosfet-switches/n_high_side.png | Bin 0 -> 10825 bytes _blog/mosfet-switches/p_high_side.png | Bin 0 -> 10724 bytes _blog/neo4j-a-star-search.md | 318 ++++++++++++++++++++++ _blog/suckless-software.md | 90 +++++++ _config.yml | 4 +- _includes/archive.html | 21 -- _includes/latest.html | 21 ++ _includes/nav.html | 4 +- _site/404.html | 2 +- _site/about/index.html | 20 +- _site/archive/arduino-due/connections.jpeg | Bin 29090 -> 0 bytes _site/archive/arduino-due/index.html | 172 ------------ _site/archive/arduino-due/schematic.png | Bin 68688 -> 0 bytes _site/archive/arduino-due/source.tar.gz | Bin 1174 -> 0 bytes _site/archive/arduino-uno/3v3.Makefile | 46 ---- _site/archive/arduino-uno/Makefile | 43 --- _site/archive/arduino-uno/breadboard.jpeg | Bin 54319 -> 0 bytes _site/archive/arduino-uno/index.html | 139 ---------- _site/archive/arduino-uno/pinout.png | Bin 247197 -> 0 bytes _site/archive/index.html | 129 --------- _site/archive/mosfet-switches/bjt.png | Bin 12838 -> 0 bytes _site/archive/mosfet-switches/index.html | 173 ------------ _site/archive/mosfet-switches/n_high_side.png | Bin 10825 -> 0 bytes _site/archive/mosfet-switches/p_high_side.png | Bin 10724 -> 0 bytes _site/archive/neo4j-a-star-search/index.html | 371 -------------------------- _site/archive/suckless-software/index.html | 142 ---------- _site/assets/css/main.css | 11 +- _site/assets/css/skeleton.css | 7 +- _site/blog/arduino-due/connections.jpeg | Bin 0 -> 29090 bytes _site/blog/arduino-due/index.html | 172 ++++++++++++ _site/blog/arduino-due/schematic.png | Bin 0 -> 68688 bytes _site/blog/arduino-due/source.tar.gz | Bin 0 -> 1174 bytes _site/blog/arduino-uno/3v3.Makefile | 46 ++++ _site/blog/arduino-uno/Makefile | 43 +++ _site/blog/arduino-uno/breadboard.jpeg | Bin 0 -> 54319 bytes _site/blog/arduino-uno/index.html | 139 ++++++++++ _site/blog/arduino-uno/pinout.png | Bin 0 -> 247197 bytes _site/blog/index.html | 129 +++++++++ _site/blog/mosfet-switches/bjt.png | Bin 0 -> 12838 bytes _site/blog/mosfet-switches/index.html | 173 ++++++++++++ _site/blog/mosfet-switches/n_high_side.png | Bin 0 -> 10825 bytes _site/blog/mosfet-switches/p_high_side.png | Bin 0 -> 10724 bytes _site/blog/neo4j-a-star-search/index.html | 371 ++++++++++++++++++++++++++ _site/blog/suckless-software/index.html | 142 ++++++++++ _site/feed.xml | 2 +- _site/index.html | 12 +- _site/posts.xml | 2 +- _site/projects/bumblebee/index.html | 2 +- _site/projects/e-reader/index.html | 2 +- _site/projects/etlas/index.html | 2 +- _site/projects/fpm-door-lock/index.html | 2 +- _site/projects/index.html | 2 +- _site/projects/matrix-digital-rain/index.html | 2 +- _site/projects/my-first-pcb/index.html | 2 +- _site/sitemap.xml | 12 +- about.html | 18 +- archive.html | 13 - assets/css/main.css | 11 +- assets/css/skeleton.css | 7 +- blog.html | 13 + index.html | 2 +- 87 files changed, 2143 insertions(+), 2131 deletions(-) delete mode 100644 _archive/arduino-due.md delete mode 100644 _archive/arduino-due/connections.jpeg delete mode 100644 _archive/arduino-due/schematic.png delete mode 100644 _archive/arduino-due/source.tar.gz delete mode 100644 _archive/arduino-uno.md delete mode 100644 _archive/arduino-uno/3v3.Makefile delete mode 100644 _archive/arduino-uno/Makefile delete mode 100644 _archive/arduino-uno/breadboard.jpeg delete mode 100644 _archive/arduino-uno/pinout.png delete mode 100644 _archive/mosfet-switches.md delete mode 100644 _archive/mosfet-switches/bjt.png delete mode 100644 _archive/mosfet-switches/n_high_side.png delete mode 100644 _archive/mosfet-switches/p_high_side.png delete mode 100644 _archive/neo4j-a-star-search.md delete mode 100644 _archive/suckless-software.md create mode 100644 _blog/arduino-due.md create mode 100644 _blog/arduino-due/connections.jpeg create mode 100644 _blog/arduino-due/schematic.png create mode 100644 _blog/arduino-due/source.tar.gz create mode 100644 _blog/arduino-uno.md create mode 100644 _blog/arduino-uno/3v3.Makefile create mode 100644 _blog/arduino-uno/Makefile create mode 100644 _blog/arduino-uno/breadboard.jpeg create mode 100644 _blog/arduino-uno/pinout.png create mode 100644 _blog/mosfet-switches.md create mode 100644 _blog/mosfet-switches/bjt.png create mode 100644 _blog/mosfet-switches/n_high_side.png create mode 100644 _blog/mosfet-switches/p_high_side.png create mode 100644 _blog/neo4j-a-star-search.md create mode 100644 _blog/suckless-software.md delete mode 100644 _includes/archive.html create mode 100644 _includes/latest.html delete mode 100644 _site/archive/arduino-due/connections.jpeg delete mode 100644 _site/archive/arduino-due/index.html delete mode 100644 _site/archive/arduino-due/schematic.png delete mode 100644 _site/archive/arduino-due/source.tar.gz delete mode 100644 _site/archive/arduino-uno/3v3.Makefile delete mode 100644 _site/archive/arduino-uno/Makefile delete mode 100644 _site/archive/arduino-uno/breadboard.jpeg delete mode 100644 _site/archive/arduino-uno/index.html delete mode 100644 _site/archive/arduino-uno/pinout.png delete mode 100644 _site/archive/index.html delete mode 100644 _site/archive/mosfet-switches/bjt.png delete mode 100644 _site/archive/mosfet-switches/index.html delete mode 100644 _site/archive/mosfet-switches/n_high_side.png delete mode 100644 _site/archive/mosfet-switches/p_high_side.png delete mode 100644 _site/archive/neo4j-a-star-search/index.html delete mode 100644 _site/archive/suckless-software/index.html create mode 100644 _site/blog/arduino-due/connections.jpeg create mode 100644 _site/blog/arduino-due/index.html create mode 100644 _site/blog/arduino-due/schematic.png create mode 100644 _site/blog/arduino-due/source.tar.gz create mode 100644 _site/blog/arduino-uno/3v3.Makefile create mode 100644 _site/blog/arduino-uno/Makefile create mode 100644 _site/blog/arduino-uno/breadboard.jpeg create mode 100644 _site/blog/arduino-uno/index.html create mode 100644 _site/blog/arduino-uno/pinout.png create mode 100644 _site/blog/index.html create mode 100644 _site/blog/mosfet-switches/bjt.png create mode 100644 _site/blog/mosfet-switches/index.html create mode 100644 _site/blog/mosfet-switches/n_high_side.png create mode 100644 _site/blog/mosfet-switches/p_high_side.png create mode 100644 _site/blog/neo4j-a-star-search/index.html create mode 100644 _site/blog/suckless-software/index.html delete mode 100644 archive.html create mode 100644 blog.html diff --git a/_archive/arduino-due.md b/_archive/arduino-due.md deleted file mode 100644 index 7c0fb12..0000000 --- a/_archive/arduino-due.md +++ /dev/null @@ -1,122 +0,0 @@ ---- -title: How to set up ATSAM3X8E microcontrollers for bare-metal programming in C -date: 2024-10-05 -layout: post ---- - -This article is a step-by-step guide for programming bare-metal ATSAM3X8E chips -found on Arduino Due boards. It also includes notes on the chip's memory layout -relevant for writing linker scripts. The steps described in this article were -tested on an OpenBSD workstation. - -## Toolchain - -To interact directly with a bare-metal ATSAM3X8E chips, we must bypass the -embedded bootloader. To do that, we need a hardware programmer capable of -communicating with the chip over the Serial Wire Debug (SWD) protocol. Since -the workstation we upload the program from presumably doesn't speak SWD, the -hardware programmer acts as a SWD-USB adapter. The ST-LINK/V2 programmer fits this -bill. - -The OpenOCD on-chip debugger software supports -ATSAM3X8E chips. OpenOCD, on startup, runs a telnet server that we can connect to -to issue commands to the ATSAM3X8E chip. OpenOCD translates plain-text commands -into the binary sequences the chip understands, and sends them over the wire. - -Finally, we need the ARM GNU Compiler -Toolchain to compile C programs for the chip. The ARM GNU compiler -toolchain and OpenOCD, as a consequence of being free software, are available -on every conceivable platform, including OpenBSD. - -## Electrical connections - -The following photos illustrate the electrical connections between the Arduino -Due, PC, and the ST-LINK/V2 programmer required to transfer a compiled program -from a PC to the MCU. - - - - - - -
- Pinout -

Wiring

- 		- Circuit -

Arduino Due

-
- -Arduino Due exposes the ATSAM3X8E's SWD interface via its DEBUG port. The -ST-LINK/v2 programmer connects to that to communicate with the chip. - -## Uploading the program - -The source.tar.gz tarball at the end of this page contains a sample C program -(the classic LED blink program) with OpenOCD configuration and linker scripts. -First, use the following command to build it: - -``` -$ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \ - -nostartfiles \ - -nostdlib \ - -o a.elf main.c -``` - -Then, open a telnet session with OpenOCD and issue the following sequence of -commands to configure the chip and upload the compiled program to it: - -``` -$ openocd -f openocd-due.cfg -$ telnet localhost 4444 - > halt - > at91sam3 gpnvm show - > at91sam3 gpnvm set 1 - > at91sam3 gpnvm show -$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit" -``` - -The first of the above commands starts OpenOCD. In the telnet session, the -first command halts the chip in preparation for receiving commands. Next, we -inspect the current GPNVM bit setting (more on this later). If the bit is unset -(the gpnvm show command returns 0), we set it to 1 and verify the update. - -The final command, issued from outside the telnet session, uploads the program -to the chip. Those are the bare minimum set of commands required to program the -chip. The AT91SAM3 flash driver section of the OpenOCD manual lists all -available commands for the ATSAM3X8E chip. - -## GPNVM bits - -By design, ARM chips boot into address 0x00000. ATSAM3X8E's memory consists of -a ROM and a dual-banked flash (flash0 and flash1), residing in different -locations of the chip's address space. The GPNVM bits control which of them -maps to 0x00000. When GPNVM1 is cleared (the default), the chip boots from the ROM, -which contains Atmel's SAM-BA bootloader. - -Conversely, when the GPNVM1 bit is 1 (and the GPNVM2 bit is 0), flash0 at -address 0x80000 maps to 0x00000. When both GPNVM bits are 0, flash1 maps to -0x00000. Since we place our program in flash0 in the linker script, we set the -GPNVM1 bit and leave the GPNVM2 bit unchanged to ensure the chip -executes our program instead of the embedded bootloader at startup. - -## Linker script - -At a minimum, the linker script must place the vector table at the first -address of the flash. This is mandatory for ARM chips unless we relocate the -vector table using the VTOR register. - -The first entry of the vector table must be the stack pointer. The stack -pointer must be initializes to the highest memory location available to -accommodate the ATSAM3X8E's descending stack. - -The second entry of the vector table must be the reset vector. In the reset -vector, we can perform tasks such as zeroing out memory and initializing -registers before passing control to the main program. - -Files: [source.tar.gz](source.tar.gz) diff --git a/_archive/arduino-due/connections.jpeg b/_archive/arduino-due/connections.jpeg deleted file mode 100644 index 081e6d4..0000000 Binary files a/_archive/arduino-due/connections.jpeg and /dev/null differ diff --git a/_archive/arduino-due/schematic.png b/_archive/arduino-due/schematic.png deleted file mode 100644 index 62ddadd..0000000 Binary files a/_archive/arduino-due/schematic.png and /dev/null differ diff --git a/_archive/arduino-due/source.tar.gz b/_archive/arduino-due/source.tar.gz deleted file mode 100644 index 496567b..0000000 Binary files a/_archive/arduino-due/source.tar.gz and /dev/null differ diff --git a/_archive/arduino-uno.md b/_archive/arduino-uno.md deleted file mode 100644 index 6534c3c..0000000 --- a/_archive/arduino-uno.md +++ /dev/null @@ -1,82 +0,0 @@ ---- -title: How to configure ATmega328P microcontrollers to run at 3.3V and 5V -date: 2025-04-10 -layout: post ---- - -This is a quick reference for wiring up ATmega328P ICs to run at 5V and 3.3V. -While the 5V configuration is common, the 3.3V configuration can be useful in -low-power applications and when interfacing with parts that themselves run at -3.3V. In this guide, the 5V setup is configured with a 16MHz crystal -oscillator, while the 3.3V configuration makes use of an 8MHz crystal -oscillator. - -The steps that follow refer to the following pinout. - - - - - - -
- Pinout -

Pinout

- 		- Circuit -

Breadboard

-
- -## 5V-16MHz configuration - -Powering ATmega328P microcontrollers with 5V is the most common setup. This is -also how Arduino Uno boards are wired. - -In this configuration, the microcontroller's pin 1 is connected to 5V via a -10kΩ resistor. Pins 9 and 10 are connected to a 16MHz crystal oscillator via -two 22pF capacitors connected to ground. The microcontroller is powered by -connecting pins 7, 20, and 21 to a 5V DC power supply. Lastly, pins 8 and 22 -are connected to ground. In addition to the these connections, which are -required, it's a good idea to add 0.1μF decoupling capacitors between pins 7, -20, and 21 and ground. - -[Here's](Makefile) a sample Makefile for compiling C programs for ATmega328P -microcontrollers using avr-gcc/avrdude toolchain. - -## 3.3V-8MHz configuration - -Electrical connections for running an ATmega328P at 3.3V are identical to that -of the 5V circuit. The only differences are that all the 5V connections are -replaced with a 3.3V power source and a 8MHz crystal oscillator takes the place -of the 16MHz crystal. - -However, standard ATmega328P chips are preconfigured to run at 5V. To run one -at 3.3V, we must first modify its fuses that control characteristics like the -BOD level. If a bootloader that expects a 16MHz clock (e.g., Arduino -bootloader) is pre-installed on the ATmega328P, it must be swapped with one -that accepts an 8MHz clock. To accomplish that, we need an in-system programmer -(ISP). - -Fortunately, we can turn an ordinary Arduino Uno board into an ISP by uploading -the 'ArduinoISP' sketch found in the Arduino IDE. The ISP communicates with the -microcontroller using a Serial Peripheral Interface (SPI). So, connect the SPI -port of the ATmega328P to that of the Arduino Uno, and the Uno's SS pin -to the ATmega328P's RESET pin. - -Power up the the ATmega328P by connecting its VCC to a 5V supply (we -can use Arduino Uno's 5V pin). From the Arduino IDE, select 'ATmega328P (3.3V, -8MHz)' for processor from the tools menu. Also from the tools menu, select -'Arduino as ISP' as programmer. Finally, upload the new bootloader by selecting -'Burn Bootloader' from the tools menu. - -The ATmega328P is now ready to run at 8MHz with a 3.3V power supply. You can -upload programs to the ATmega328P as you normally would using avrdude. -[Here's](3v3.Makefile) a sample Makefile with adjusted parameters (e.g., baud -rate) for an 8MHz clock. - -## Remarks - -In both configurations, if you intend to use the ATmega328P's analog-to-digital -converter with the internal 1.1V or AVcc voltage as reference, do -not connect AREF (pin 21) to Vcc. Refer to section 23.5.2 in the -datasheet for more information. - diff --git a/_archive/arduino-uno/3v3.Makefile b/_archive/arduino-uno/3v3.Makefile deleted file mode 100644 index 4ca89d4..0000000 --- a/_archive/arduino-uno/3v3.Makefile +++ /dev/null @@ -1,46 +0,0 @@ -CC = avr-gcc -MCU = atmega328p -PORT = /dev/cuaU0 -TARGET = app - -SRC = main.c -OBJ = $(SRC:.c=.o) - -CFLAGS = -std=gnu99 -CFLAGS += -Os -CFLAGS += -Wall -CFLAGS += -mmcu=$(MCU) -CFLAGS += -DBAUD=57600 -CFLAGS += -DF_CPU=8000000UL -CFLAGS += -ffunction-sections -fdata-sections - -LDFLAGS = -mmcu=$(MCU) -LDFLAGS += -Wl,--gc-sections - -HEX_FLAGS = -O ihex -HEX_FLAGS += -j .text -j .data - -AVRDUDE_FLAGS = -p $(MCU) -AVRDUDE_FLAGS += -c arduino -AVRDUDE_FLAGS += -b 57600 -AVRDUDE_FLAGS += -P $(PORT) -AVRDUDE_FLAGS += -D -U - -%.o: %.c - $(CC) $(CFLAGS) -c -o $@ $< - -elf: $(OBJ) - $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf - -hex: elf - avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex - -upload: hex - avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i - -.PHONY: clean - -clean: - rm -f *.o *.elf *.hex - - diff --git a/_archive/arduino-uno/Makefile b/_archive/arduino-uno/Makefile deleted file mode 100644 index 9db7b09..0000000 --- a/_archive/arduino-uno/Makefile +++ /dev/null @@ -1,43 +0,0 @@ -CC = avr-gcc -MCU = atmega328p -PORT = /dev/cuaU0 -TARGET = app - -SRC = main.c -OBJ = $(SRC:.c=.o) - -CFLAGS = -std=gnu99 -CFLAGS += -Os -CFLAGS += -Wall -CFLAGS += -mmcu=$(MCU) -CFLAGS += -DBAUD=115200 -CFLAGS += -DF_CPU=16000000UL -CFLAGS += -ffunction-sections -fdata-sections - -LDFLAGS = -mmcu=$(MCU) -LDFLAGS += -Wl,--gc-sections - -HEX_FLAGS = -O ihex -HEX_FLAGS += -j .text -j .data - -AVRDUDE_FLAGS = -p $(MCU) -AVRDUDE_FLAGS += -c arduino -AVRDUDE_FLAGS += -P $(PORT) -AVRDUDE_FLAGS += -D -U - -%.o: %.c - $(CC) $(CFLAGS) -c -o $@ $< - -elf: $(OBJ) - $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf - -hex: elf - avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex - -upload: hex - avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i - -.PHONY: clean - -clean: - rm *.o *.elf *.hex diff --git a/_archive/arduino-uno/breadboard.jpeg b/_archive/arduino-uno/breadboard.jpeg deleted file mode 100644 index bd74907..0000000 Binary files a/_archive/arduino-uno/breadboard.jpeg and /dev/null differ diff --git a/_archive/arduino-uno/pinout.png b/_archive/arduino-uno/pinout.png deleted file mode 100644 index 59acfbc..0000000 Binary files a/_archive/arduino-uno/pinout.png and /dev/null differ diff --git a/_archive/mosfet-switches.md b/_archive/mosfet-switches.md deleted file mode 100644 index bb3514d..0000000 --- a/_archive/mosfet-switches.md +++ /dev/null @@ -1,123 +0,0 @@ ---- -title: MOSFETs as electronic switches -date: 2025-06-22 -layout: post ---- - -Recently, I needed a low-power circuit for one of my battery-operated projects. -Much of the system's power savings depended on its ability to electronically -switch off components, such as servos, that draw high levels of quiescent -currents. My search for a solution led me to MOSFETs, transistors capable of -controlling circuits operating at voltages far above their own. - -## Acknowledgments - -This article is a summary of what I learnt about using MOSFETs as switches. -I'm not an electronics engineer, and this is not an authoritative guide. The -circuits in this post must be considered within the narrow context in which -I've used them. All credits for the schematics belong to Simon Fitch. - -## Preamble - -For a typical MOSFET-based switch, we can connect a GPIO pin of a -microcontroller to the gate of a logic-level N-channel MOSFET placed on the low -side of the load and tie the gate and the drain pins of the MOSFET with a -pull-down resistor. This would work as long as the power supplies of the -microcontroller and the load don't share a common ground. Things become more -complicated when they do (e.g., controlling power to a component driven by the -same microcontroller). - -In that scenario, the source potential visible to the load is the difference -between the gate and the threshold potentials of the MOSFET. For example, when -the gate and the threshold potentials are 3.3 V and 1.5 V, the potential the -load sees is 1.8 V. So, to use a low-side N-channel MOSFET, we need the gate -potential to be higher than the source potential, which may not always be -practical. The alternative would be a hide-side switch. - -## P-channel high-side switch - -The following schematic shows how a high-side P-channel MOSFET (M1) could -switch power to a 6 V servo driven by a 3.3 V MCU. - -![P-channel high-side switching circuit](p_high_side.png) - -When the microcontroller outputs low, the M2 N-channel MOSFET stops conducting. -The R1 resistor pulls the gate of the M1 P-channel MOSFET up to +6 V, switching -the servo off. When the microcontroller outputs high on the GPIO pin, M2's -source-drain connection starts conducting, causing M1's gate potential to drop -to 0 V, which switches on power to the servo. - -## N-channel high-side switch - -The P-channel high-side switch would be the typical architecture for our use -case. However, if we have access to a potential high enough to safely raise the -gate potential above the threshold such that their difference outputs the source -potential required to drive the load, we can switch on the high side using an -N-channel MOSFET: - -![N-channel high-side switching circuit](n_high_side.png) - -In the schematic, both M1 and M2 are N-channel MOSFETs. When the -microcontroller output is low, M2 stops conducting. This causes the M1's gate -potential to rise above the threshold, turning the servo on. Conversely, a high -output on the GPIO line switches M2 on, which lowers M1's gate potential. This -switches the servo off. The R2 pull-up resistor prevents the high impedance of -the output pins at power-up from switching the servo on. - -Both topologies require M2 to act as a level converter between circuits -containing the microcontroller and the servo, converting between 0 V and +6 V -or +9 V. M2 is a low-power signal converter carrying less than a milliamp of -current. The gate-source threshold voltage of M2 must be lower than the MCU's -supply voltage. 2N7000, 2N7002, and BSS138 are popular choices for M2. - -The D1 flyback diodes used in the two topologies safeguard the MOSFET from -voltage spikes caused by inductive loads such as servos. - -## A BJT alternative - -A Bipolar Junction Transistor (BJT) is a simpler, cheaper, and more widely -available type of transistor that can be used as a switch. - -![BJT architecture](bjt.png) - -In the schematic, when the MCU outputs high, Q2 starts conducting. Q2 amplifies -Q1's base current. Unlike MOSFETs, which are voltage-driven, BJTs are driven by -base current. Resistors R3 and R4 must be chosen carefully to output the -desired base currents. "How to choose a -transistor as a switch" is an excellent guide on using BJTs as electronic -switches. - -## Which topology to choose? - -The professional community appears to prefer MOSFETs over BJTs. MOSFETs are -more efficient when the switch is on. However, they are more challenging to -drive, especially with a 3.3 V MCU, due to the VGS potentials -required to achieve specified RDS(on) values (i.e., to turn them on -fully). - -N-channel MOSFETs have lower on-resistance values, making them more efficient -than P-channel ones. They are also cheaper. However, they are harder to drive -on the high side as their gate potential must be higher than the source -potential. This often requires extra circuitry such as MOSFET drivers. - -## Further reading - - - Different MOSFET - topologies - - How to read - MOSFET datasheets - - How to use a - transistor as a switch - - Guide to - selecting and controlling a MOSFET for 3.3 VDC logic applications - - Driving a large - relay from a 3.3 VDC microcontroller using an NPN Darlington transistor diff --git a/_archive/mosfet-switches/bjt.png b/_archive/mosfet-switches/bjt.png deleted file mode 100644 index 9858fa7..0000000 Binary files a/_archive/mosfet-switches/bjt.png and /dev/null differ diff --git a/_archive/mosfet-switches/n_high_side.png b/_archive/mosfet-switches/n_high_side.png deleted file mode 100644 index c851768..0000000 Binary files a/_archive/mosfet-switches/n_high_side.png and /dev/null differ diff --git a/_archive/mosfet-switches/p_high_side.png b/_archive/mosfet-switches/p_high_side.png deleted file mode 100644 index 9f5397a..0000000 Binary files a/_archive/mosfet-switches/p_high_side.png and /dev/null differ diff --git a/_archive/neo4j-a-star-search.md b/_archive/neo4j-a-star-search.md deleted file mode 100644 index 117931b..0000000 --- a/_archive/neo4j-a-star-search.md +++ /dev/null @@ -1,318 +0,0 @@ ---- -title: Neo4J A* search -date: 2025-09-14 -layout: post ---- - -Back in 2018, we used Neo4J graph database to track the -movement of marine vessels. We were interested in the shortest path a ship -could take through a network of about 13,000 route points. Algorithms based on -graph theory, such as A* search, provide optimal solutions to such problems. -In other words, the set of route points lends itself well to a model based on -graphs. - -A graph is a finite set of vertices, and a subset of vertex pairs (edges). -Edges can have weights. In the case of vessel tracking, the route points form -the vertices of a graph; the routes between them, the edges; and the distances -between them are the weights. For different reasons, people are interested in -minimizing (or maximizing) the weight of a path through a set of vertices. For -instance, we may want to find the shortest path between two ports. - -Given such a graph, an algorithm like Dijkstra's search could compute the -shortest path between two vertices. In fact, this was the algorithm Neo4J -shipped with at the time. One drawback of Dijkstra's algorithm is that it -computes all the shortest paths from the source to all other vertices before -terminating at the destination vertex. The exhaustive nature of this search -limited our search to about 4,000 route points. - -The following enhancement to Dijkstra's search, also known as the A* search, -employs a heuristic to steer the search in the direction of the destination -more quickly. In the case of our network of vessels, which are on the earth's -surface, spherical distance is a good candidate for a heuristic: - -``` -package org.neo4j.graphalgo.impl; - -import java.util.stream.Stream; -import java.util.stream.StreamSupport; - -import org.neo4j.graphalgo.api.Graph; -import org.neo4j.graphalgo.core.utils.ProgressLogger; -import org.neo4j.graphalgo.core.utils.queue.IntPriorityQueue; -import org.neo4j.graphalgo.core.utils.queue.SharedIntPriorityQueue; -import org.neo4j.graphalgo.core.utils.traverse.SimpleBitSet; -import org.neo4j.graphdb.Direction; -import org.neo4j.graphdb.Node; -import org.neo4j.kernel.internal.GraphDatabaseAPI; - -import com.carrotsearch.hppc.IntArrayDeque; -import com.carrotsearch.hppc.IntDoubleMap; -import com.carrotsearch.hppc.IntDoubleScatterMap; -import com.carrotsearch.hppc.IntIntMap; -import com.carrotsearch.hppc.IntIntScatterMap; - -public class ShortestPathAStar extends Algorithm { - - private final GraphDatabaseAPI dbService; - private static final int PATH_END = -1; - - private Graph graph; - private final int nodeCount; - private IntDoubleMap gCosts; - private IntDoubleMap fCosts; - private double totalCost; - private IntPriorityQueue openNodes; - private IntIntMap path; - private IntArrayDeque shortestPath; - private SimpleBitSet closedNodes; - private final ProgressLogger progressLogger; - - public static final double NO_PATH_FOUND = -1.0; - - public ShortestPathAStar( - final Graph graph, - final GraphDatabaseAPI dbService) { - - this.graph = graph; - this.dbService = dbService; - - nodeCount = Math.toIntExact(graph.nodeCount()); - gCosts = new IntDoubleScatterMap(nodeCount); - fCosts = new IntDoubleScatterMap(nodeCount); - openNodes = SharedIntPriorityQueue.min( - nodeCount, - fCosts, - Double.MAX_VALUE); - path = new IntIntScatterMap(nodeCount); - closedNodes = new SimpleBitSet(nodeCount); - shortestPath = new IntArrayDeque(); - progressLogger = getProgressLogger(); - } - - public ShortestPathAStar compute( - final long startNode, - final long goalNode, - final String propertyKeyLat, - final String propertyKeyLon, - final Direction direction) { - - reset(); - - final int startNodeInternal = - graph.toMappedNodeId(startNode); - final double startNodeLat = - getNodeCoordinate(startNodeInternal, propertyKeyLat); - final double startNodeLon = - getNodeCoordinate(startNodeInternal, propertyKeyLon); - - final int goalNodeInternal = - graph.toMappedNodeId(goalNode); - final double goalNodeLat = - getNodeCoordinate(goalNodeInternal, propertyKeyLat); - final double goalNodeLon = - getNodeCoordinate(goalNodeInternal, propertyKeyLon); - - final double initialHeuristic = - computeHeuristic(startNodeLat, - startNodeLon, - goalNodeLat, - goalNodeLon); - - gCosts.put(startNodeInternal, 0.0); - fCosts.put(startNodeInternal, initialHeuristic); - openNodes.add(startNodeInternal, 0.0); - - run(goalNodeInternal, - propertyKeyLat, - propertyKeyLon, - direction); - - if (path.containsKey(goalNodeInternal)) { - totalCost = gCosts.get(goalNodeInternal); - int node = goalNodeInternal; - while (node != PATH_END) { - shortestPath.addFirst(node); - node = path.getOrDefault(node, PATH_END); - } - } - return this; - } - - private void run( - final int goalNodeId, - final String propertyKeyLat, - final String propertyKeyLon, - final Direction direction) { - - final double goalLat = - getNodeCoordinate(goalNodeId, propertyKeyLat); - final double goalLon = - getNodeCoordinate(goalNodeId, propertyKeyLon); - - while (!openNodes.isEmpty() && running()) { - int currentNodeId = openNodes.pop(); - if (currentNodeId == goalNodeId) { - return; - } - - closedNodes.put(currentNodeId); - - double currentNodeCost = - this.gCosts.getOrDefault( - currentNodeId, - Double.MAX_VALUE); - - graph.forEachRelationship( - currentNodeId, - direction, - (source, target, relationshipId, weight) -> { - double neighbourLat = - getNodeCoordinate(target, propertyKeyLat); - double neighbourLon = - getNodeCoordinate(target, propertyKeyLon); - double heuristic = - computeHeuristic( - neighbourLat, - neighbourLon, - goalLat, - goalLon); - - updateCosts( - source, - target, - weight + currentNodeCost, - heuristic); - - if (!closedNodes.contains(target)) { - openNodes.add(target, 0); - } - return true; - }); - - progressLogger.logProgress( - (double) currentNodeId / (nodeCount - 1)); - } - } - - private double computeHeuristic( - final double lat1, - final double lon1, - final double lat2, - final double lon2) { - - final int earthRadius = 6371; - final double kmToNM = 0.539957; - final double latDistance = Math.toRadians(lat2 - lat1); - final double lonDistance = Math.toRadians(lon2 - lon1); - final double a = Math.sin(latDistance / 2) - * Math.sin(latDistance / 2) - + Math.cos(Math.toRadians(lat1)) - * Math.cos(Math.toRadians(lat2)) - * Math.sin(lonDistance / 2) - * Math.sin(lonDistance / 2); - final double c = 2 - * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)); - final double distance = earthRadius * c * kmToNM; - return distance; - } - - private double getNodeCoordinate( - final int nodeId, - final String coordinateType) { - - final long neo4jId = graph.toOriginalNodeId(nodeId); - final Node node = dbService.getNodeById(neo4jId); - return (double) node.getProperty(coordinateType); - } - - private void updateCosts( - final int source, - final int target, - final double newCost, - final double heuristic) { - - final double oldCost = - gCosts.getOrDefault(target, Double.MAX_VALUE); - - if (newCost < oldCost) { - gCosts.put(target, newCost); - fCosts.put(target, newCost + heuristic); - path.put(target, source); - } - } - - private void reset() { - closedNodes.clear(); - openNodes.clear(); - gCosts.clear(); - fCosts.clear(); - path.clear(); - shortestPath.clear(); - totalCost = NO_PATH_FOUND; - } - - public Stream resultStream() { - return StreamSupport.stream( - shortestPath.spliterator(), false) - .map(cursor -> new Result( - graph.toOriginalNodeId(cursor.value), - gCosts.get(cursor.value))); - } - - public IntArrayDeque getFinalPath() { - return shortestPath; - } - - public double getTotalCost() { - return totalCost; - } - - public int getPathLength() { - return shortestPath.size(); - } - - @Override - public ShortestPathAStar me() { - return this; - } - - @Override - public ShortestPathAStar release() { - graph = null; - gCosts = null; - fCosts = null; - openNodes = null; - path = null; - shortestPath = null; - closedNodes = null; - return this; - } - - public static class Result { - - /** - * the neo4j node id - */ - public final Long nodeId; - - /** - * cost to reach the node from startNode - */ - public final Double cost; - - public Result(Long nodeId, Double cost) { - this.nodeId = nodeId; - this.cost = cost; - } - } -} -``` - -The heuristic function is domain-specific. If chosen wisely, it can -significantly speed up the search. In our case, we achieved a 300x speedup, -enabling us to expand our search from 4,000 to 13,000 route points. The v3.4.0 of the -Neo4J graph algorithms shipped with the A* search algorithm. - diff --git a/_archive/suckless-software.md b/_archive/suckless-software.md deleted file mode 100644 index 86fb5bc..0000000 --- a/_archive/suckless-software.md +++ /dev/null @@ -1,90 +0,0 @@ ---- -title: How I manage Suckless software packages -date: 2025-11-30 -layout: post ---- - -Since suckless software requires users to modify the -source code and recompile to customize, I need a way to maintain patches over -the long term while retaining the ability to upgrade the software as new -versions are released. - -## Initial setup - -When using a suckless program, I usually begin by cloning the project and -setting the remote URL to push a copy of the source code with my patches to my -own git repository: - -``` -git clone git://git.suckless.org/dwm -git reset --hard -git remote set-url --push origin git@git.asciimx.com:/repos/dwm -``` - -This way, I can pull updates from the upstream project whenever I want, while -committing my changes to my own git repository. The git reset command aligns my -branch head with a stable release before applying patches or installing the -software. - -If all I want to do is reconfigure the software (e.g., change key bindings), -which is what I need most of the time, the recommended approach is to modify -the config.h file. If the config.h isn't yet in the project, the following -command generates it from the defaults and compiles the software using `make -clean ` here `` is the name of the application (e.g., dwm) -found in the Makefile. I modify the resulting config.h file and run `make clean -install` to install the software before committing and pushing my changes to my -git repo. - -## dwm and slstatus - -Since dwm and slstatus are always running, `make install` will likely fail for -them. The operating system will prevent the installer from replacing running -executables with new ones. Hence, we must first stop the running instances of -these programs (Mod + Shift + q). Then, switch to a tty (Ctrl + Alt + F1), -log in, and change the directory to where dwm/slstatus is. We can run `make -install` to install the software and switch back to the graphical session -(Ctrl + Alt + F5). - -The key combinations for switching to the tty and back may differ across -systems. The ones listed above are for OpenBSD. - -## Subsequent upgrades - -When suckless releases a new version, I run `git pull --rebase` to fetch the -upstream changes and rebase my patches on top of them. Because I tend to use -stable versions, I perform another interactive rebase to drop the commits -between the latest stable version tag and my patch before installing the -software. - -Commit log before upgrading: - -``` -dt236 My patch. -3fkdf Version 6.5. -``` - -Commit log after pulling: - -``` -w467d My patch. -gh25g A commit. -g525g Another commit. -3fkdf Version 6.6. -vd425 Old commit. -q12vu Another old commit. -3fkdf Version 6.5. -``` - -Commit log after the interactive rebase: - -``` -h57jh My patch. -3fkdf Version 6.6. -vd425 Old commit. -q12vu Another old commit. -3fkdf Version 6.5. -``` - -And finally, commit and push all the changes to my own git repository. - diff --git a/_blog/arduino-due.md b/_blog/arduino-due.md new file mode 100644 index 0000000..7c0fb12 --- /dev/null +++ b/_blog/arduino-due.md @@ -0,0 +1,122 @@ +--- +title: How to set up ATSAM3X8E microcontrollers for bare-metal programming in C +date: 2024-10-05 +layout: post +--- + +This article is a step-by-step guide for programming bare-metal ATSAM3X8E chips +found on Arduino Due boards. It also includes notes on the chip's memory layout +relevant for writing linker scripts. The steps described in this article were +tested on an OpenBSD workstation. + +## Toolchain + +To interact directly with a bare-metal ATSAM3X8E chips, we must bypass the +embedded bootloader. To do that, we need a hardware programmer capable of +communicating with the chip over the Serial Wire Debug (SWD) protocol. Since +the workstation we upload the program from presumably doesn't speak SWD, the +hardware programmer acts as a SWD-USB adapter. The ST-LINK/V2 programmer fits this +bill. + +The OpenOCD on-chip debugger software supports +ATSAM3X8E chips. OpenOCD, on startup, runs a telnet server that we can connect to +to issue commands to the ATSAM3X8E chip. OpenOCD translates plain-text commands +into the binary sequences the chip understands, and sends them over the wire. + +Finally, we need the ARM GNU Compiler +Toolchain to compile C programs for the chip. The ARM GNU compiler +toolchain and OpenOCD, as a consequence of being free software, are available +on every conceivable platform, including OpenBSD. + +## Electrical connections + +The following photos illustrate the electrical connections between the Arduino +Due, PC, and the ST-LINK/V2 programmer required to transfer a compiled program +from a PC to the MCU. + + + + + + +
+ Pinout +

Wiring

+ 		+ Circuit +

Arduino Due

+
+ +Arduino Due exposes the ATSAM3X8E's SWD interface via its DEBUG port. The +ST-LINK/v2 programmer connects to that to communicate with the chip. + +## Uploading the program + +The source.tar.gz tarball at the end of this page contains a sample C program +(the classic LED blink program) with OpenOCD configuration and linker scripts. +First, use the following command to build it: + +``` +$ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \ + -nostartfiles \ + -nostdlib \ + -o a.elf main.c +``` + +Then, open a telnet session with OpenOCD and issue the following sequence of +commands to configure the chip and upload the compiled program to it: + +``` +$ openocd -f openocd-due.cfg +$ telnet localhost 4444 + > halt + > at91sam3 gpnvm show + > at91sam3 gpnvm set 1 + > at91sam3 gpnvm show +$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit" +``` + +The first of the above commands starts OpenOCD. In the telnet session, the +first command halts the chip in preparation for receiving commands. Next, we +inspect the current GPNVM bit setting (more on this later). If the bit is unset +(the gpnvm show command returns 0), we set it to 1 and verify the update. + +The final command, issued from outside the telnet session, uploads the program +to the chip. Those are the bare minimum set of commands required to program the +chip. The AT91SAM3 flash driver section of the OpenOCD manual lists all +available commands for the ATSAM3X8E chip. + +## GPNVM bits + +By design, ARM chips boot into address 0x00000. ATSAM3X8E's memory consists of +a ROM and a dual-banked flash (flash0 and flash1), residing in different +locations of the chip's address space. The GPNVM bits control which of them +maps to 0x00000. When GPNVM1 is cleared (the default), the chip boots from the ROM, +which contains Atmel's SAM-BA bootloader. + +Conversely, when the GPNVM1 bit is 1 (and the GPNVM2 bit is 0), flash0 at +address 0x80000 maps to 0x00000. When both GPNVM bits are 0, flash1 maps to +0x00000. Since we place our program in flash0 in the linker script, we set the +GPNVM1 bit and leave the GPNVM2 bit unchanged to ensure the chip +executes our program instead of the embedded bootloader at startup. + +## Linker script + +At a minimum, the linker script must place the vector table at the first +address of the flash. This is mandatory for ARM chips unless we relocate the +vector table using the VTOR register. + +The first entry of the vector table must be the stack pointer. The stack +pointer must be initializes to the highest memory location available to +accommodate the ATSAM3X8E's descending stack. + +The second entry of the vector table must be the reset vector. In the reset +vector, we can perform tasks such as zeroing out memory and initializing +registers before passing control to the main program. + +Files: [source.tar.gz](source.tar.gz) diff --git a/_blog/arduino-due/connections.jpeg b/_blog/arduino-due/connections.jpeg new file mode 100644 index 0000000..081e6d4 Binary files /dev/null and b/_blog/arduino-due/connections.jpeg differ diff --git a/_blog/arduino-due/schematic.png b/_blog/arduino-due/schematic.png new file mode 100644 index 0000000..62ddadd Binary files /dev/null and b/_blog/arduino-due/schematic.png differ diff --git a/_blog/arduino-due/source.tar.gz b/_blog/arduino-due/source.tar.gz new file mode 100644 index 0000000..496567b Binary files /dev/null and b/_blog/arduino-due/source.tar.gz differ diff --git a/_blog/arduino-uno.md b/_blog/arduino-uno.md new file mode 100644 index 0000000..6534c3c --- /dev/null +++ b/_blog/arduino-uno.md @@ -0,0 +1,82 @@ +--- +title: How to configure ATmega328P microcontrollers to run at 3.3V and 5V +date: 2025-04-10 +layout: post +--- + +This is a quick reference for wiring up ATmega328P ICs to run at 5V and 3.3V. +While the 5V configuration is common, the 3.3V configuration can be useful in +low-power applications and when interfacing with parts that themselves run at +3.3V. In this guide, the 5V setup is configured with a 16MHz crystal +oscillator, while the 3.3V configuration makes use of an 8MHz crystal +oscillator. + +The steps that follow refer to the following pinout. + + + + + + +
+ Pinout +

Pinout

+ 		+ Circuit +

Breadboard

+
+ +## 5V-16MHz configuration + +Powering ATmega328P microcontrollers with 5V is the most common setup. This is +also how Arduino Uno boards are wired. + +In this configuration, the microcontroller's pin 1 is connected to 5V via a +10kΩ resistor. Pins 9 and 10 are connected to a 16MHz crystal oscillator via +two 22pF capacitors connected to ground. The microcontroller is powered by +connecting pins 7, 20, and 21 to a 5V DC power supply. Lastly, pins 8 and 22 +are connected to ground. In addition to the these connections, which are +required, it's a good idea to add 0.1μF decoupling capacitors between pins 7, +20, and 21 and ground. + +[Here's](Makefile) a sample Makefile for compiling C programs for ATmega328P +microcontrollers using avr-gcc/avrdude toolchain. + +## 3.3V-8MHz configuration + +Electrical connections for running an ATmega328P at 3.3V are identical to that +of the 5V circuit. The only differences are that all the 5V connections are +replaced with a 3.3V power source and a 8MHz crystal oscillator takes the place +of the 16MHz crystal. + +However, standard ATmega328P chips are preconfigured to run at 5V. To run one +at 3.3V, we must first modify its fuses that control characteristics like the +BOD level. If a bootloader that expects a 16MHz clock (e.g., Arduino +bootloader) is pre-installed on the ATmega328P, it must be swapped with one +that accepts an 8MHz clock. To accomplish that, we need an in-system programmer +(ISP). + +Fortunately, we can turn an ordinary Arduino Uno board into an ISP by uploading +the 'ArduinoISP' sketch found in the Arduino IDE. The ISP communicates with the +microcontroller using a Serial Peripheral Interface (SPI). So, connect the SPI +port of the ATmega328P to that of the Arduino Uno, and the Uno's SS pin +to the ATmega328P's RESET pin. + +Power up the the ATmega328P by connecting its VCC to a 5V supply (we +can use Arduino Uno's 5V pin). From the Arduino IDE, select 'ATmega328P (3.3V, +8MHz)' for processor from the tools menu. Also from the tools menu, select +'Arduino as ISP' as programmer. Finally, upload the new bootloader by selecting +'Burn Bootloader' from the tools menu. + +The ATmega328P is now ready to run at 8MHz with a 3.3V power supply. You can +upload programs to the ATmega328P as you normally would using avrdude. +[Here's](3v3.Makefile) a sample Makefile with adjusted parameters (e.g., baud +rate) for an 8MHz clock. + +## Remarks + +In both configurations, if you intend to use the ATmega328P's analog-to-digital +converter with the internal 1.1V or AVcc voltage as reference, do +not connect AREF (pin 21) to Vcc. Refer to section 23.5.2 in the +datasheet for more information. + diff --git a/_blog/arduino-uno/3v3.Makefile b/_blog/arduino-uno/3v3.Makefile new file mode 100644 index 0000000..4ca89d4 --- /dev/null +++ b/_blog/arduino-uno/3v3.Makefile @@ -0,0 +1,46 @@ +CC = avr-gcc +MCU = atmega328p +PORT = /dev/cuaU0 +TARGET = app + +SRC = main.c +OBJ = $(SRC:.c=.o) + +CFLAGS = -std=gnu99 +CFLAGS += -Os +CFLAGS += -Wall +CFLAGS += -mmcu=$(MCU) +CFLAGS += -DBAUD=57600 +CFLAGS += -DF_CPU=8000000UL +CFLAGS += -ffunction-sections -fdata-sections + +LDFLAGS = -mmcu=$(MCU) +LDFLAGS += -Wl,--gc-sections + +HEX_FLAGS = -O ihex +HEX_FLAGS += -j .text -j .data + +AVRDUDE_FLAGS = -p $(MCU) +AVRDUDE_FLAGS += -c arduino +AVRDUDE_FLAGS += -b 57600 +AVRDUDE_FLAGS += -P $(PORT) +AVRDUDE_FLAGS += -D -U + +%.o: %.c + $(CC) $(CFLAGS) -c -o $@ $< + +elf: $(OBJ) + $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf + +hex: elf + avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex + +upload: hex + avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i + +.PHONY: clean + +clean: + rm -f *.o *.elf *.hex + + diff --git a/_blog/arduino-uno/Makefile b/_blog/arduino-uno/Makefile new file mode 100644 index 0000000..9db7b09 --- /dev/null +++ b/_blog/arduino-uno/Makefile @@ -0,0 +1,43 @@ +CC = avr-gcc +MCU = atmega328p +PORT = /dev/cuaU0 +TARGET = app + +SRC = main.c +OBJ = $(SRC:.c=.o) + +CFLAGS = -std=gnu99 +CFLAGS += -Os +CFLAGS += -Wall +CFLAGS += -mmcu=$(MCU) +CFLAGS += -DBAUD=115200 +CFLAGS += -DF_CPU=16000000UL +CFLAGS += -ffunction-sections -fdata-sections + +LDFLAGS = -mmcu=$(MCU) +LDFLAGS += -Wl,--gc-sections + +HEX_FLAGS = -O ihex +HEX_FLAGS += -j .text -j .data + +AVRDUDE_FLAGS = -p $(MCU) +AVRDUDE_FLAGS += -c arduino +AVRDUDE_FLAGS += -P $(PORT) +AVRDUDE_FLAGS += -D -U + +%.o: %.c + $(CC) $(CFLAGS) -c -o $@ $< + +elf: $(OBJ) + $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf + +hex: elf + avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex + +upload: hex + avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i + +.PHONY: clean + +clean: + rm *.o *.elf *.hex diff --git a/_blog/arduino-uno/breadboard.jpeg b/_blog/arduino-uno/breadboard.jpeg new file mode 100644 index 0000000..bd74907 Binary files /dev/null and b/_blog/arduino-uno/breadboard.jpeg differ diff --git a/_blog/arduino-uno/pinout.png b/_blog/arduino-uno/pinout.png new file mode 100644 index 0000000..59acfbc Binary files /dev/null and b/_blog/arduino-uno/pinout.png differ diff --git a/_blog/mosfet-switches.md b/_blog/mosfet-switches.md new file mode 100644 index 0000000..bb3514d --- /dev/null +++ b/_blog/mosfet-switches.md @@ -0,0 +1,123 @@ +--- +title: MOSFETs as electronic switches +date: 2025-06-22 +layout: post +--- + +Recently, I needed a low-power circuit for one of my battery-operated projects. +Much of the system's power savings depended on its ability to electronically +switch off components, such as servos, that draw high levels of quiescent +currents. My search for a solution led me to MOSFETs, transistors capable of +controlling circuits operating at voltages far above their own. + +## Acknowledgments + +This article is a summary of what I learnt about using MOSFETs as switches. +I'm not an electronics engineer, and this is not an authoritative guide. The +circuits in this post must be considered within the narrow context in which +I've used them. All credits for the schematics belong to Simon Fitch. + +## Preamble + +For a typical MOSFET-based switch, we can connect a GPIO pin of a +microcontroller to the gate of a logic-level N-channel MOSFET placed on the low +side of the load and tie the gate and the drain pins of the MOSFET with a +pull-down resistor. This would work as long as the power supplies of the +microcontroller and the load don't share a common ground. Things become more +complicated when they do (e.g., controlling power to a component driven by the +same microcontroller). + +In that scenario, the source potential visible to the load is the difference +between the gate and the threshold potentials of the MOSFET. For example, when +the gate and the threshold potentials are 3.3 V and 1.5 V, the potential the +load sees is 1.8 V. So, to use a low-side N-channel MOSFET, we need the gate +potential to be higher than the source potential, which may not always be +practical. The alternative would be a hide-side switch. + +## P-channel high-side switch + +The following schematic shows how a high-side P-channel MOSFET (M1) could +switch power to a 6 V servo driven by a 3.3 V MCU. + +![P-channel high-side switching circuit](p_high_side.png) + +When the microcontroller outputs low, the M2 N-channel MOSFET stops conducting. +The R1 resistor pulls the gate of the M1 P-channel MOSFET up to +6 V, switching +the servo off. When the microcontroller outputs high on the GPIO pin, M2's +source-drain connection starts conducting, causing M1's gate potential to drop +to 0 V, which switches on power to the servo. + +## N-channel high-side switch + +The P-channel high-side switch would be the typical architecture for our use +case. However, if we have access to a potential high enough to safely raise the +gate potential above the threshold such that their difference outputs the source +potential required to drive the load, we can switch on the high side using an +N-channel MOSFET: + +![N-channel high-side switching circuit](n_high_side.png) + +In the schematic, both M1 and M2 are N-channel MOSFETs. When the +microcontroller output is low, M2 stops conducting. This causes the M1's gate +potential to rise above the threshold, turning the servo on. Conversely, a high +output on the GPIO line switches M2 on, which lowers M1's gate potential. This +switches the servo off. The R2 pull-up resistor prevents the high impedance of +the output pins at power-up from switching the servo on. + +Both topologies require M2 to act as a level converter between circuits +containing the microcontroller and the servo, converting between 0 V and +6 V +or +9 V. M2 is a low-power signal converter carrying less than a milliamp of +current. The gate-source threshold voltage of M2 must be lower than the MCU's +supply voltage. 2N7000, 2N7002, and BSS138 are popular choices for M2. + +The D1 flyback diodes used in the two topologies safeguard the MOSFET from +voltage spikes caused by inductive loads such as servos. + +## A BJT alternative + +A Bipolar Junction Transistor (BJT) is a simpler, cheaper, and more widely +available type of transistor that can be used as a switch. + +![BJT architecture](bjt.png) + +In the schematic, when the MCU outputs high, Q2 starts conducting. Q2 amplifies +Q1's base current. Unlike MOSFETs, which are voltage-driven, BJTs are driven by +base current. Resistors R3 and R4 must be chosen carefully to output the +desired base currents. "How to choose a +transistor as a switch" is an excellent guide on using BJTs as electronic +switches. + +## Which topology to choose? + +The professional community appears to prefer MOSFETs over BJTs. MOSFETs are +more efficient when the switch is on. However, they are more challenging to +drive, especially with a 3.3 V MCU, due to the VGS potentials +required to achieve specified RDS(on) values (i.e., to turn them on +fully). + +N-channel MOSFETs have lower on-resistance values, making them more efficient +than P-channel ones. They are also cheaper. However, they are harder to drive +on the high side as their gate potential must be higher than the source +potential. This often requires extra circuitry such as MOSFET drivers. + +## Further reading + + - Different MOSFET + topologies + - How to read + MOSFET datasheets + - How to use a + transistor as a switch + - Guide to + selecting and controlling a MOSFET for 3.3 VDC logic applications + - Driving a large + relay from a 3.3 VDC microcontroller using an NPN Darlington transistor diff --git a/_blog/mosfet-switches/bjt.png b/_blog/mosfet-switches/bjt.png new file mode 100644 index 0000000..9858fa7 Binary files /dev/null and b/_blog/mosfet-switches/bjt.png differ diff --git a/_blog/mosfet-switches/n_high_side.png b/_blog/mosfet-switches/n_high_side.png new file mode 100644 index 0000000..c851768 Binary files /dev/null and b/_blog/mosfet-switches/n_high_side.png differ diff --git a/_blog/mosfet-switches/p_high_side.png b/_blog/mosfet-switches/p_high_side.png new file mode 100644 index 0000000..9f5397a Binary files /dev/null and b/_blog/mosfet-switches/p_high_side.png differ diff --git a/_blog/neo4j-a-star-search.md b/_blog/neo4j-a-star-search.md new file mode 100644 index 0000000..117931b --- /dev/null +++ b/_blog/neo4j-a-star-search.md @@ -0,0 +1,318 @@ +--- +title: Neo4J A* search +date: 2025-09-14 +layout: post +--- + +Back in 2018, we used Neo4J graph database to track the +movement of marine vessels. We were interested in the shortest path a ship +could take through a network of about 13,000 route points. Algorithms based on +graph theory, such as A* search, provide optimal solutions to such problems. +In other words, the set of route points lends itself well to a model based on +graphs. + +A graph is a finite set of vertices, and a subset of vertex pairs (edges). +Edges can have weights. In the case of vessel tracking, the route points form +the vertices of a graph; the routes between them, the edges; and the distances +between them are the weights. For different reasons, people are interested in +minimizing (or maximizing) the weight of a path through a set of vertices. For +instance, we may want to find the shortest path between two ports. + +Given such a graph, an algorithm like Dijkstra's search could compute the +shortest path between two vertices. In fact, this was the algorithm Neo4J +shipped with at the time. One drawback of Dijkstra's algorithm is that it +computes all the shortest paths from the source to all other vertices before +terminating at the destination vertex. The exhaustive nature of this search +limited our search to about 4,000 route points. + +The following enhancement to Dijkstra's search, also known as the A* search, +employs a heuristic to steer the search in the direction of the destination +more quickly. In the case of our network of vessels, which are on the earth's +surface, spherical distance is a good candidate for a heuristic: + +``` +package org.neo4j.graphalgo.impl; + +import java.util.stream.Stream; +import java.util.stream.StreamSupport; + +import org.neo4j.graphalgo.api.Graph; +import org.neo4j.graphalgo.core.utils.ProgressLogger; +import org.neo4j.graphalgo.core.utils.queue.IntPriorityQueue; +import org.neo4j.graphalgo.core.utils.queue.SharedIntPriorityQueue; +import org.neo4j.graphalgo.core.utils.traverse.SimpleBitSet; +import org.neo4j.graphdb.Direction; +import org.neo4j.graphdb.Node; +import org.neo4j.kernel.internal.GraphDatabaseAPI; + +import com.carrotsearch.hppc.IntArrayDeque; +import com.carrotsearch.hppc.IntDoubleMap; +import com.carrotsearch.hppc.IntDoubleScatterMap; +import com.carrotsearch.hppc.IntIntMap; +import com.carrotsearch.hppc.IntIntScatterMap; + +public class ShortestPathAStar extends Algorithm { + + private final GraphDatabaseAPI dbService; + private static final int PATH_END = -1; + + private Graph graph; + private final int nodeCount; + private IntDoubleMap gCosts; + private IntDoubleMap fCosts; + private double totalCost; + private IntPriorityQueue openNodes; + private IntIntMap path; + private IntArrayDeque shortestPath; + private SimpleBitSet closedNodes; + private final ProgressLogger progressLogger; + + public static final double NO_PATH_FOUND = -1.0; + + public ShortestPathAStar( + final Graph graph, + final GraphDatabaseAPI dbService) { + + this.graph = graph; + this.dbService = dbService; + + nodeCount = Math.toIntExact(graph.nodeCount()); + gCosts = new IntDoubleScatterMap(nodeCount); + fCosts = new IntDoubleScatterMap(nodeCount); + openNodes = SharedIntPriorityQueue.min( + nodeCount, + fCosts, + Double.MAX_VALUE); + path = new IntIntScatterMap(nodeCount); + closedNodes = new SimpleBitSet(nodeCount); + shortestPath = new IntArrayDeque(); + progressLogger = getProgressLogger(); + } + + public ShortestPathAStar compute( + final long startNode, + final long goalNode, + final String propertyKeyLat, + final String propertyKeyLon, + final Direction direction) { + + reset(); + + final int startNodeInternal = + graph.toMappedNodeId(startNode); + final double startNodeLat = + getNodeCoordinate(startNodeInternal, propertyKeyLat); + final double startNodeLon = + getNodeCoordinate(startNodeInternal, propertyKeyLon); + + final int goalNodeInternal = + graph.toMappedNodeId(goalNode); + final double goalNodeLat = + getNodeCoordinate(goalNodeInternal, propertyKeyLat); + final double goalNodeLon = + getNodeCoordinate(goalNodeInternal, propertyKeyLon); + + final double initialHeuristic = + computeHeuristic(startNodeLat, + startNodeLon, + goalNodeLat, + goalNodeLon); + + gCosts.put(startNodeInternal, 0.0); + fCosts.put(startNodeInternal, initialHeuristic); + openNodes.add(startNodeInternal, 0.0); + + run(goalNodeInternal, + propertyKeyLat, + propertyKeyLon, + direction); + + if (path.containsKey(goalNodeInternal)) { + totalCost = gCosts.get(goalNodeInternal); + int node = goalNodeInternal; + while (node != PATH_END) { + shortestPath.addFirst(node); + node = path.getOrDefault(node, PATH_END); + } + } + return this; + } + + private void run( + final int goalNodeId, + final String propertyKeyLat, + final String propertyKeyLon, + final Direction direction) { + + final double goalLat = + getNodeCoordinate(goalNodeId, propertyKeyLat); + final double goalLon = + getNodeCoordinate(goalNodeId, propertyKeyLon); + + while (!openNodes.isEmpty() && running()) { + int currentNodeId = openNodes.pop(); + if (currentNodeId == goalNodeId) { + return; + } + + closedNodes.put(currentNodeId); + + double currentNodeCost = + this.gCosts.getOrDefault( + currentNodeId, + Double.MAX_VALUE); + + graph.forEachRelationship( + currentNodeId, + direction, + (source, target, relationshipId, weight) -> { + double neighbourLat = + getNodeCoordinate(target, propertyKeyLat); + double neighbourLon = + getNodeCoordinate(target, propertyKeyLon); + double heuristic = + computeHeuristic( + neighbourLat, + neighbourLon, + goalLat, + goalLon); + + updateCosts( + source, + target, + weight + currentNodeCost, + heuristic); + + if (!closedNodes.contains(target)) { + openNodes.add(target, 0); + } + return true; + }); + + progressLogger.logProgress( + (double) currentNodeId / (nodeCount - 1)); + } + } + + private double computeHeuristic( + final double lat1, + final double lon1, + final double lat2, + final double lon2) { + + final int earthRadius = 6371; + final double kmToNM = 0.539957; + final double latDistance = Math.toRadians(lat2 - lat1); + final double lonDistance = Math.toRadians(lon2 - lon1); + final double a = Math.sin(latDistance / 2) + * Math.sin(latDistance / 2) + + Math.cos(Math.toRadians(lat1)) + * Math.cos(Math.toRadians(lat2)) + * Math.sin(lonDistance / 2) + * Math.sin(lonDistance / 2); + final double c = 2 + * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)); + final double distance = earthRadius * c * kmToNM; + return distance; + } + + private double getNodeCoordinate( + final int nodeId, + final String coordinateType) { + + final long neo4jId = graph.toOriginalNodeId(nodeId); + final Node node = dbService.getNodeById(neo4jId); + return (double) node.getProperty(coordinateType); + } + + private void updateCosts( + final int source, + final int target, + final double newCost, + final double heuristic) { + + final double oldCost = + gCosts.getOrDefault(target, Double.MAX_VALUE); + + if (newCost < oldCost) { + gCosts.put(target, newCost); + fCosts.put(target, newCost + heuristic); + path.put(target, source); + } + } + + private void reset() { + closedNodes.clear(); + openNodes.clear(); + gCosts.clear(); + fCosts.clear(); + path.clear(); + shortestPath.clear(); + totalCost = NO_PATH_FOUND; + } + + public Stream resultStream() { + return StreamSupport.stream( + shortestPath.spliterator(), false) + .map(cursor -> new Result( + graph.toOriginalNodeId(cursor.value), + gCosts.get(cursor.value))); + } + + public IntArrayDeque getFinalPath() { + return shortestPath; + } + + public double getTotalCost() { + return totalCost; + } + + public int getPathLength() { + return shortestPath.size(); + } + + @Override + public ShortestPathAStar me() { + return this; + } + + @Override + public ShortestPathAStar release() { + graph = null; + gCosts = null; + fCosts = null; + openNodes = null; + path = null; + shortestPath = null; + closedNodes = null; + return this; + } + + public static class Result { + + /** + * the neo4j node id + */ + public final Long nodeId; + + /** + * cost to reach the node from startNode + */ + public final Double cost; + + public Result(Long nodeId, Double cost) { + this.nodeId = nodeId; + this.cost = cost; + } + } +} +``` + +The heuristic function is domain-specific. If chosen wisely, it can +significantly speed up the search. In our case, we achieved a 300x speedup, +enabling us to expand our search from 4,000 to 13,000 route points. The v3.4.0 of the +Neo4J graph algorithms shipped with the A* search algorithm. + diff --git a/_blog/suckless-software.md b/_blog/suckless-software.md new file mode 100644 index 0000000..86fb5bc --- /dev/null +++ b/_blog/suckless-software.md @@ -0,0 +1,90 @@ +--- +title: How I manage Suckless software packages +date: 2025-11-30 +layout: post +--- + +Since suckless software requires users to modify the +source code and recompile to customize, I need a way to maintain patches over +the long term while retaining the ability to upgrade the software as new +versions are released. + +## Initial setup + +When using a suckless program, I usually begin by cloning the project and +setting the remote URL to push a copy of the source code with my patches to my +own git repository: + +``` +git clone git://git.suckless.org/dwm +git reset --hard +git remote set-url --push origin git@git.asciimx.com:/repos/dwm +``` + +This way, I can pull updates from the upstream project whenever I want, while +committing my changes to my own git repository. The git reset command aligns my +branch head with a stable release before applying patches or installing the +software. + +If all I want to do is reconfigure the software (e.g., change key bindings), +which is what I need most of the time, the recommended approach is to modify +the config.h file. If the config.h isn't yet in the project, the following +command generates it from the defaults and compiles the software using `make +clean ` here `` is the name of the application (e.g., dwm) +found in the Makefile. I modify the resulting config.h file and run `make clean +install` to install the software before committing and pushing my changes to my +git repo. + +## dwm and slstatus + +Since dwm and slstatus are always running, `make install` will likely fail for +them. The operating system will prevent the installer from replacing running +executables with new ones. Hence, we must first stop the running instances of +these programs (Mod + Shift + q). Then, switch to a tty (Ctrl + Alt + F1), +log in, and change the directory to where dwm/slstatus is. We can run `make +install` to install the software and switch back to the graphical session +(Ctrl + Alt + F5). + +The key combinations for switching to the tty and back may differ across +systems. The ones listed above are for OpenBSD. + +## Subsequent upgrades + +When suckless releases a new version, I run `git pull --rebase` to fetch the +upstream changes and rebase my patches on top of them. Because I tend to use +stable versions, I perform another interactive rebase to drop the commits +between the latest stable version tag and my patch before installing the +software. + +Commit log before upgrading: + +``` +dt236 My patch. +3fkdf Version 6.5. +``` + +Commit log after pulling: + +``` +w467d My patch. +gh25g A commit. +g525g Another commit. +3fkdf Version 6.6. +vd425 Old commit. +q12vu Another old commit. +3fkdf Version 6.5. +``` + +Commit log after the interactive rebase: + +``` +h57jh My patch. +3fkdf Version 6.6. +vd425 Old commit. +q12vu Another old commit. +3fkdf Version 6.5. +``` + +And finally, commit and push all the changes to my own git repository. + diff --git a/_config.yml b/_config.yml index aec1c06..a56ae2a 100644 --- a/_config.yml +++ b/_config.yml @@ -4,14 +4,14 @@ author: W. D. Sadeep Madurange permalink: pretty collections: - archive: + blog: output: true projects: output: true feed: collections: - archive: + blog: path: "/feed.xml" posts: path: "/posts.xml" diff --git a/_includes/archive.html b/_includes/archive.html deleted file mode 100644 index 1b8c9c9..0000000 --- a/_includes/archive.html +++ /dev/null @@ -1,21 +0,0 @@ -
- - - {% assign posts = site.archive | sort: 'date' | reverse %} - {% for post in posts limit: include.limit %} - - - - - - - {% endfor %} - -
- {{ post.title }} - - - - -
-
diff --git a/_includes/latest.html b/_includes/latest.html new file mode 100644 index 0000000..6b6e114 --- /dev/null +++ b/_includes/latest.html @@ -0,0 +1,21 @@ +
+ + + {% assign posts = site.blog | sort: 'date' | reverse %} + {% for post in posts limit: include.limit %} + + + + + + + {% endfor %} + +
+ {{ post.title }} + + + + +
+
diff --git a/_includes/nav.html b/_includes/nav.html index adfa919..bd53f55 100644 --- a/_includes/nav.html +++ b/_includes/nav.html @@ -4,8 +4,8 @@
  • hme
    • -
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  • poc diff --git a/_site/404.html b/_site/404.html index c3a9e02..272c760 100644 --- a/_site/404.html +++ b/_site/404.html @@ -20,7 +20,7 @@ hme
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  • poc diff --git a/_site/about/index.html b/_site/about/index.html index 15a648e..060f09d 100644 --- a/_site/about/index.html +++ b/_site/about/index.html @@ -20,7 +20,7 @@ hme
  • - blg + blg
  • poc @@ -42,18 +42,20 @@

    - Site structure:
    -

      -
    • hme: Home page, listing latest articles.
      • -
    • blg: Notes and tutorials about software and embedded systems.
      • -
    • poc: Projects, prototypes, and experiments.
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    • abt: Site information.
      • -
    • rss: RSS (Atom) feed.
      • -
    Email: sadeep@asciimx.com [GPG]

    +

    Navigation

    + +
      +
    • hme: Home page, listing latest articles.
      • +
    • blg: Notes and tutorials about software and embedded systems.
      • +
    • poc: Projects, prototypes, and experiments.
      • +
    • abt: Site information.
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    About site

    diff --git a/_site/archive/arduino-due/connections.jpeg b/_site/archive/arduino-due/connections.jpeg deleted file mode 100644 index 081e6d4..0000000 Binary files a/_site/archive/arduino-due/connections.jpeg and /dev/null differ diff --git a/_site/archive/arduino-due/index.html b/_site/archive/arduino-due/index.html deleted file mode 100644 index e146957..0000000 --- a/_site/archive/arduino-due/index.html +++ /dev/null @@ -1,172 +0,0 @@ - - - - - How to set up ATSAM3X8E microcontrollers for bare-metal programming in C - - - - - How to set up ATSAM3X8E microcontrollers for bare-metal programming in C - - - - - - - - - -

    - - - -
    -
    -
    -

    HOW TO SET UP ATSAM3X8E MICROCONTROLLERS FOR BARE-METAL PROGRAMMING IN C

    -
    05 OCTOBER 2024
    -
    -

    This article is a step-by-step guide for programming bare-metal ATSAM3X8E chips -found on Arduino Due boards. It also includes notes on the chip’s memory layout -relevant for writing linker scripts. The steps described in this article were -tested on an OpenBSD workstation.

    - -

    Toolchain

    - -

    To interact directly with a bare-metal ATSAM3X8E chips, we must bypass the -embedded bootloader. To do that, we need a hardware programmer capable of -communicating with the chip over the Serial Wire Debug (SWD) protocol. Since -the workstation we upload the program from presumably doesn’t speak SWD, the -hardware programmer acts as a SWD-USB adapter. The ST-LINK/V2 programmer fits this -bill.

    - -

    The OpenOCD on-chip debugger software supports -ATSAM3X8E chips. OpenOCD, on startup, runs a telnet server that we can connect to -to issue commands to the ATSAM3X8E chip. OpenOCD translates plain-text commands -into the binary sequences the chip understands, and sends them over the wire.

    - -

    Finally, we need the ARM GNU Compiler -Toolchain to compile C programs for the chip. The ARM GNU compiler -toolchain and OpenOCD, as a consequence of being free software, are available -on every conceivable platform, including OpenBSD.

    - -

    Electrical connections

    - -

    The following photos illustrate the electrical connections between the Arduino -Due, PC, and the ST-LINK/V2 programmer required to transfer a compiled program -from a PC to the MCU.

    - - - - - - -
    - Pinout -

    Wiring

    -     		- Circuit -

    Arduino Due

    -
    - -

    Arduino Due exposes the ATSAM3X8E’s SWD interface via its DEBUG port. The -ST-LINK/v2 programmer connects to that to communicate with the chip.

    - -

    Uploading the program

    - -

    The source.tar.gz tarball at the end of this page contains a sample C program -(the classic LED blink program) with OpenOCD configuration and linker scripts. -First, use the following command to build it:

    - -
    $ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \
-    -nostartfiles \
-    -nostdlib \
-    -o a.elf main.c
-
    - -

    Then, open a telnet session with OpenOCD and issue the following sequence of -commands to configure the chip and upload the compiled program to it:

    - -
    $ openocd -f openocd-due.cfg
-$ telnet localhost 4444
-  > halt
-  > at91sam3 gpnvm show
-  > at91sam3 gpnvm set 1
-  > at91sam3 gpnvm show
-$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit"
-
    - -

    The first of the above commands starts OpenOCD. In the telnet session, the -first command halts the chip in preparation for receiving commands. Next, we -inspect the current GPNVM bit setting (more on this later). If the bit is unset -(the gpnvm show command returns 0), we set it to 1 and verify the update.

    - -

    The final command, issued from outside the telnet session, uploads the program -to the chip. Those are the bare minimum set of commands required to program the -chip. The AT91SAM3 flash driver section of the OpenOCD manual lists all -available commands for the ATSAM3X8E chip.

    - -

    GPNVM bits

    - -

    By design, ARM chips boot into address 0x00000. ATSAM3X8E’s memory consists of -a ROM and a dual-banked flash (flash0 and flash1), residing in different -locations of the chip’s address space. The GPNVM bits control which of them -maps to 0x00000. When GPNVM1 is cleared (the default), the chip boots from the ROM, -which contains Atmel’s SAM-BA bootloader.

    - -

    Conversely, when the GPNVM1 bit is 1 (and the GPNVM2 bit is 0), flash0 at -address 0x80000 maps to 0x00000. When both GPNVM bits are 0, flash1 maps to -0x00000. Since we place our program in flash0 in the linker script, we set the -GPNVM1 bit and leave the GPNVM2 bit unchanged to ensure the chip -executes our program instead of the embedded bootloader at startup.

    - -

    Linker script

    - -

    At a minimum, the linker script must place the vector table at the first -address of the flash. This is mandatory for ARM chips unless we relocate the -vector table using the VTOR register.

    - -

    The first entry of the vector table must be the stack pointer. The stack -pointer must be initializes to the highest memory location available to -accommodate the ATSAM3X8E’s descending stack.

    - -

    The second entry of the vector table must be the reset vector. In the reset -vector, we can perform tasks such as zeroing out memory and initializing -registers before passing control to the main program.

    - -

    Files: source.tar.gz

    -
    -

    by W. D. Sadeep Madurange

    -
    -
    -
    - -
    -
    -
    -

    © ASCIIMX - 2025

    -
    -
    -
    - - - - diff --git a/_site/archive/arduino-due/schematic.png b/_site/archive/arduino-due/schematic.png deleted file mode 100644 index 62ddadd..0000000 Binary files a/_site/archive/arduino-due/schematic.png and /dev/null differ diff --git a/_site/archive/arduino-due/source.tar.gz b/_site/archive/arduino-due/source.tar.gz deleted file mode 100644 index 496567b..0000000 Binary files a/_site/archive/arduino-due/source.tar.gz and /dev/null differ diff --git a/_site/archive/arduino-uno/3v3.Makefile b/_site/archive/arduino-uno/3v3.Makefile deleted file mode 100644 index 4ca89d4..0000000 --- a/_site/archive/arduino-uno/3v3.Makefile +++ /dev/null @@ -1,46 +0,0 @@ -CC = avr-gcc -MCU = atmega328p -PORT = /dev/cuaU0 -TARGET = app - -SRC = main.c -OBJ = $(SRC:.c=.o) - -CFLAGS = -std=gnu99 -CFLAGS += -Os -CFLAGS += -Wall -CFLAGS += -mmcu=$(MCU) -CFLAGS += -DBAUD=57600 -CFLAGS += -DF_CPU=8000000UL -CFLAGS += -ffunction-sections -fdata-sections - -LDFLAGS = -mmcu=$(MCU) -LDFLAGS += -Wl,--gc-sections - -HEX_FLAGS = -O ihex -HEX_FLAGS += -j .text -j .data - -AVRDUDE_FLAGS = -p $(MCU) -AVRDUDE_FLAGS += -c arduino -AVRDUDE_FLAGS += -b 57600 -AVRDUDE_FLAGS += -P $(PORT) -AVRDUDE_FLAGS += -D -U - -%.o: %.c - $(CC) $(CFLAGS) -c -o $@ $< - -elf: $(OBJ) - $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf - -hex: elf - avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex - -upload: hex - avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i - -.PHONY: clean - -clean: - rm -f *.o *.elf *.hex - - diff --git a/_site/archive/arduino-uno/Makefile b/_site/archive/arduino-uno/Makefile deleted file mode 100644 index 9db7b09..0000000 --- a/_site/archive/arduino-uno/Makefile +++ /dev/null @@ -1,43 +0,0 @@ -CC = avr-gcc -MCU = atmega328p -PORT = /dev/cuaU0 -TARGET = app - -SRC = main.c -OBJ = $(SRC:.c=.o) - -CFLAGS = -std=gnu99 -CFLAGS += -Os -CFLAGS += -Wall -CFLAGS += -mmcu=$(MCU) -CFLAGS += -DBAUD=115200 -CFLAGS += -DF_CPU=16000000UL -CFLAGS += -ffunction-sections -fdata-sections - -LDFLAGS = -mmcu=$(MCU) -LDFLAGS += -Wl,--gc-sections - -HEX_FLAGS = -O ihex -HEX_FLAGS += -j .text -j .data - -AVRDUDE_FLAGS = -p $(MCU) -AVRDUDE_FLAGS += -c arduino -AVRDUDE_FLAGS += -P $(PORT) -AVRDUDE_FLAGS += -D -U - -%.o: %.c - $(CC) $(CFLAGS) -c -o $@ $< - -elf: $(OBJ) - $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf - -hex: elf - avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex - -upload: hex - avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i - -.PHONY: clean - -clean: - rm *.o *.elf *.hex diff --git a/_site/archive/arduino-uno/breadboard.jpeg b/_site/archive/arduino-uno/breadboard.jpeg deleted file mode 100644 index bd74907..0000000 Binary files a/_site/archive/arduino-uno/breadboard.jpeg and /dev/null differ diff --git a/_site/archive/arduino-uno/index.html b/_site/archive/arduino-uno/index.html deleted file mode 100644 index 2b4f64d..0000000 --- a/_site/archive/arduino-uno/index.html +++ /dev/null @@ -1,139 +0,0 @@ - - - - - How to configure ATmega328P microcontrollers to run at 3.3V and 5V - - - - - How to configure ATmega328P microcontrollers to run at 3.3V and 5V - - - - - - - - - - - - - -
    -
    -
    -

    HOW TO CONFIGURE ATMEGA328P MICROCONTROLLERS TO RUN AT 3.3V AND 5V

    -
    10 APRIL 2025
    -
    -

    This is a quick reference for wiring up ATmega328P ICs to run at 5V and 3.3V. -While the 5V configuration is common, the 3.3V configuration can be useful in -low-power applications and when interfacing with parts that themselves run at -3.3V. In this guide, the 5V setup is configured with a 16MHz crystal -oscillator, while the 3.3V configuration makes use of an 8MHz crystal -oscillator.

    - -

    The steps that follow refer to the following pinout.

    - - - - - - -
    - Pinout -

    Pinout

    -     		- Circuit -

    Breadboard

    -
    - -

    5V-16MHz configuration

    - -

    Powering ATmega328P microcontrollers with 5V is the most common setup. This is -also how Arduino Uno boards are wired.

    - -

    In this configuration, the microcontroller’s pin 1 is connected to 5V via a -10kΩ resistor. Pins 9 and 10 are connected to a 16MHz crystal oscillator via -two 22pF capacitors connected to ground. The microcontroller is powered by -connecting pins 7, 20, and 21 to a 5V DC power supply. Lastly, pins 8 and 22 -are connected to ground. In addition to the these connections, which are -required, it’s a good idea to add 0.1μF decoupling capacitors between pins 7, -20, and 21 and ground.

    - -

    Here’s a sample Makefile for compiling C programs for ATmega328P -microcontrollers using avr-gcc/avrdude toolchain.

    - -

    3.3V-8MHz configuration

    - -

    Electrical connections for running an ATmega328P at 3.3V are identical to that -of the 5V circuit. The only differences are that all the 5V connections are -replaced with a 3.3V power source and a 8MHz crystal oscillator takes the place -of the 16MHz crystal.

    - -

    However, standard ATmega328P chips are preconfigured to run at 5V. To run one -at 3.3V, we must first modify its fuses that control characteristics like the -BOD level. If a bootloader that expects a 16MHz clock (e.g., Arduino -bootloader) is pre-installed on the ATmega328P, it must be swapped with one -that accepts an 8MHz clock. To accomplish that, we need an in-system programmer -(ISP).

    - -

    Fortunately, we can turn an ordinary Arduino Uno board into an ISP by uploading -the ‘ArduinoISP’ sketch found in the Arduino IDE. The ISP communicates with the -microcontroller using a Serial Peripheral Interface (SPI). So, connect the SPI -port of the ATmega328P to that of the Arduino Uno, and the Uno’s SS pin -to the ATmega328P’s RESET pin.

    - -

    Power up the the ATmega328P by connecting its VCC to a 5V supply (we -can use Arduino Uno’s 5V pin). From the Arduino IDE, select ‘ATmega328P (3.3V, -8MHz)’ for processor from the tools menu. Also from the tools menu, select -‘Arduino as ISP’ as programmer. Finally, upload the new bootloader by selecting -‘Burn Bootloader’ from the tools menu.

    - -

    The ATmega328P is now ready to run at 8MHz with a 3.3V power supply. You can -upload programs to the ATmega328P as you normally would using avrdude. -Here’s a sample Makefile with adjusted parameters (e.g., baud -rate) for an 8MHz clock.

    - -

    Remarks

    - -

    In both configurations, if you intend to use the ATmega328P’s analog-to-digital -converter with the internal 1.1V or AVcc voltage as reference, do -not connect AREF (pin 21) to Vcc. Refer to section 23.5.2 in the -datasheet for more information.

    - -
    -

    by W. D. Sadeep Madurange

    -
    -
    -
    - -
    -
    -
    -

    © ASCIIMX - 2025

    -
    -
    -
    - - - - diff --git a/_site/archive/arduino-uno/pinout.png b/_site/archive/arduino-uno/pinout.png deleted file mode 100644 index 59acfbc..0000000 Binary files a/_site/archive/arduino-uno/pinout.png and /dev/null differ diff --git a/_site/archive/index.html b/_site/archive/index.html deleted file mode 100644 index e739320..0000000 --- a/_site/archive/index.html +++ /dev/null @@ -1,129 +0,0 @@ - - - - - - - Archive - - - - - - - - - - - - -
    - -

    Archive

    - -
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    - How I manage Suckless software packages - - - - -
    - Neo4J A* search - - - - -
    - MOSFETs as electronic switches - - - - -
    - How to configure ATmega328P microcontrollers to run at 3.3V and 5V - - - - -
    - How to set up ATSAM3X8E microcontrollers for bare-metal programming in C - - - - -
    -
    - - -
    -
    - -
    -
    -
    -

    © ASCIIMX - 2025

    -
    -
    -
    - - - - diff --git a/_site/archive/mosfet-switches/bjt.png b/_site/archive/mosfet-switches/bjt.png deleted file mode 100644 index 9858fa7..0000000 Binary files a/_site/archive/mosfet-switches/bjt.png and /dev/null differ diff --git a/_site/archive/mosfet-switches/index.html b/_site/archive/mosfet-switches/index.html deleted file mode 100644 index 902d813..0000000 --- a/_site/archive/mosfet-switches/index.html +++ /dev/null @@ -1,173 +0,0 @@ - - - - - MOSFETs as electronic switches - - - - - MOSFETs as electronic switches - - - - - - - - - - - - - -
    -
    -
    -

    MOSFETS AS ELECTRONIC SWITCHES

    -
    22 JUNE 2025
    -
    -

    Recently, I needed a low-power circuit for one of my battery-operated projects. -Much of the system’s power savings depended on its ability to electronically -switch off components, such as servos, that draw high levels of quiescent -currents. My search for a solution led me to MOSFETs, transistors capable of -controlling circuits operating at voltages far above their own.

    - -

    Acknowledgments

    - -

    This article is a summary of what I learnt about using MOSFETs as switches. -I’m not an electronics engineer, and this is not an authoritative guide. The -circuits in this post must be considered within the narrow context in which -I’ve used them. All credits for the schematics belong to Simon Fitch.

    - -

    Preamble

    - -

    For a typical MOSFET-based switch, we can connect a GPIO pin of a -microcontroller to the gate of a logic-level N-channel MOSFET placed on the low -side of the load and tie the gate and the drain pins of the MOSFET with a -pull-down resistor. This would work as long as the power supplies of the -microcontroller and the load don’t share a common ground. Things become more -complicated when they do (e.g., controlling power to a component driven by the -same microcontroller).

    - -

    In that scenario, the source potential visible to the load is the difference -between the gate and the threshold potentials of the MOSFET. For example, when -the gate and the threshold potentials are 3.3 V and 1.5 V, the potential the -load sees is 1.8 V. So, to use a low-side N-channel MOSFET, we need the gate -potential to be higher than the source potential, which may not always be -practical. The alternative would be a hide-side switch.

    - -

    P-channel high-side switch

    - -

    The following schematic shows how a high-side P-channel MOSFET (M1) could -switch power to a 6 V servo driven by a 3.3 V MCU.

    - -

    P-channel high-side switching circuit

    - -

    When the microcontroller outputs low, the M2 N-channel MOSFET stops conducting. -The R1 resistor pulls the gate of the M1 P-channel MOSFET up to +6 V, switching -the servo off. When the microcontroller outputs high on the GPIO pin, M2’s -source-drain connection starts conducting, causing M1’s gate potential to drop -to 0 V, which switches on power to the servo.

    - -

    N-channel high-side switch

    - -

    The P-channel high-side switch would be the typical architecture for our use -case. However, if we have access to a potential high enough to safely raise the -gate potential above the threshold such that their difference outputs the source -potential required to drive the load, we can switch on the high side using an -N-channel MOSFET:

    - -

    N-channel high-side switching circuit

    - -

    In the schematic, both M1 and M2 are N-channel MOSFETs. When the -microcontroller output is low, M2 stops conducting. This causes the M1’s gate -potential to rise above the threshold, turning the servo on. Conversely, a high -output on the GPIO line switches M2 on, which lowers M1’s gate potential. This -switches the servo off. The R2 pull-up resistor prevents the high impedance of -the output pins at power-up from switching the servo on.

    - -

    Both topologies require M2 to act as a level converter between circuits -containing the microcontroller and the servo, converting between 0 V and +6 V -or +9 V. M2 is a low-power signal converter carrying less than a milliamp of -current. The gate-source threshold voltage of M2 must be lower than the MCU’s -supply voltage. 2N7000, 2N7002, and BSS138 are popular choices for M2.

    - -

    The D1 flyback diodes used in the two topologies safeguard the MOSFET from -voltage spikes caused by inductive loads such as servos.

    - -

    A BJT alternative

    - -

    A Bipolar Junction Transistor (BJT) is a simpler, cheaper, and more widely -available type of transistor that can be used as a switch.

    - -

    BJT architecture

    - -

    In the schematic, when the MCU outputs high, Q2 starts conducting. Q2 amplifies -Q1’s base current. Unlike MOSFETs, which are voltage-driven, BJTs are driven by -base current. Resistors R3 and R4 must be chosen carefully to output the -desired base currents. “How to choose a -transistor as a switch” is an excellent guide on using BJTs as electronic -switches.

    - -

    Which topology to choose?

    - -

    The professional community appears to prefer MOSFETs over BJTs. MOSFETs are -more efficient when the switch is on. However, they are more challenging to -drive, especially with a 3.3 V MCU, due to the VGS potentials -required to achieve specified RDS(on) values (i.e., to turn them on -fully).

    - -

    N-channel MOSFETs have lower on-resistance values, making them more efficient -than P-channel ones. They are also cheaper. However, they are harder to drive -on the high side as their gate potential must be higher than the source -potential. This often requires extra circuitry such as MOSFET drivers.

    - -

    Further reading

    - - -
    -

    by W. D. Sadeep Madurange

    -
    -
    -
    - -
    -
    -
    -

    © ASCIIMX - 2025

    -
    -
    -
    - - - - diff --git a/_site/archive/mosfet-switches/n_high_side.png b/_site/archive/mosfet-switches/n_high_side.png deleted file mode 100644 index c851768..0000000 Binary files a/_site/archive/mosfet-switches/n_high_side.png and /dev/null differ diff --git a/_site/archive/mosfet-switches/p_high_side.png b/_site/archive/mosfet-switches/p_high_side.png deleted file mode 100644 index 9f5397a..0000000 Binary files a/_site/archive/mosfet-switches/p_high_side.png and /dev/null differ diff --git a/_site/archive/neo4j-a-star-search/index.html b/_site/archive/neo4j-a-star-search/index.html deleted file mode 100644 index e0696aa..0000000 --- a/_site/archive/neo4j-a-star-search/index.html +++ /dev/null @@ -1,371 +0,0 @@ - - - - - Neo4J A* search - - - - - Neo4J A* search - - - - - - - - - - - - - -
    -
    -
    -

    NEO4J A* SEARCH

    -
    14 SEPTEMBER 2025
    -
    -

    Back in 2018, we used Neo4J graph database to track the -movement of marine vessels. We were interested in the shortest path a ship -could take through a network of about 13,000 route points. Algorithms based on -graph theory, such as A* search, provide optimal solutions to such problems. -In other words, the set of route points lends itself well to a model based on -graphs.

    - -

    A graph is a finite set of vertices, and a subset of vertex pairs (edges). -Edges can have weights. In the case of vessel tracking, the route points form -the vertices of a graph; the routes between them, the edges; and the distances -between them are the weights. For different reasons, people are interested in -minimizing (or maximizing) the weight of a path through a set of vertices. For -instance, we may want to find the shortest path between two ports.

    - -

    Given such a graph, an algorithm like Dijkstra’s search could compute the -shortest path between two vertices. In fact, this was the algorithm Neo4J -shipped with at the time. One drawback of Dijkstra’s algorithm is that it -computes all the shortest paths from the source to all other vertices before -terminating at the destination vertex. The exhaustive nature of this search -limited our search to about 4,000 route points.

    - -

    The following enhancement to Dijkstra’s search, also known as the A* search, -employs a heuristic to steer the search in the direction of the destination -more quickly. In the case of our network of vessels, which are on the earth’s -surface, spherical distance is a good candidate for a heuristic:

    - -
    package org.neo4j.graphalgo.impl;
-
-import java.util.stream.Stream;
-import java.util.stream.StreamSupport;
-
-import org.neo4j.graphalgo.api.Graph;
-import org.neo4j.graphalgo.core.utils.ProgressLogger;
-import org.neo4j.graphalgo.core.utils.queue.IntPriorityQueue;
-import org.neo4j.graphalgo.core.utils.queue.SharedIntPriorityQueue;
-import org.neo4j.graphalgo.core.utils.traverse.SimpleBitSet;
-import org.neo4j.graphdb.Direction;
-import org.neo4j.graphdb.Node;
-import org.neo4j.kernel.internal.GraphDatabaseAPI;
-
-import com.carrotsearch.hppc.IntArrayDeque;
-import com.carrotsearch.hppc.IntDoubleMap;
-import com.carrotsearch.hppc.IntDoubleScatterMap;
-import com.carrotsearch.hppc.IntIntMap;
-import com.carrotsearch.hppc.IntIntScatterMap;
-
-public class ShortestPathAStar extends Algorithm<ShortestPathAStar> {
-    
-    private final GraphDatabaseAPI dbService;
-    private static final int PATH_END = -1;
-    
-    private Graph graph;
-    private final int nodeCount;
-    private IntDoubleMap gCosts;
-    private IntDoubleMap fCosts;
-    private double totalCost;
-    private IntPriorityQueue openNodes;
-    private IntIntMap path;
-    private IntArrayDeque shortestPath;
-    private SimpleBitSet closedNodes;
-    private final ProgressLogger progressLogger;
-    
-    public static final double NO_PATH_FOUND = -1.0;
-    
-    public ShortestPathAStar(
-        final Graph graph,
-        final GraphDatabaseAPI dbService) {
-
-        this.graph = graph;
-        this.dbService = dbService;
-
-        nodeCount = Math.toIntExact(graph.nodeCount());
-        gCosts = new IntDoubleScatterMap(nodeCount);
-        fCosts = new IntDoubleScatterMap(nodeCount);
-        openNodes = SharedIntPriorityQueue.min(
-            nodeCount,
-            fCosts,
-            Double.MAX_VALUE);
-        path = new IntIntScatterMap(nodeCount);
-        closedNodes = new SimpleBitSet(nodeCount);
-        shortestPath = new IntArrayDeque();
-        progressLogger = getProgressLogger();
-    }
-    
-    public ShortestPathAStar compute(
-        final long startNode,
-        final long goalNode,
-        final String propertyKeyLat,
-        final String propertyKeyLon,
-        final Direction direction) {
-
-        reset();
-
-        final int startNodeInternal = 
-            graph.toMappedNodeId(startNode);
-        final double startNodeLat =
-            getNodeCoordinate(startNodeInternal, propertyKeyLat);
-        final double startNodeLon = 
-            getNodeCoordinate(startNodeInternal, propertyKeyLon);
-
-        final int goalNodeInternal =
-            graph.toMappedNodeId(goalNode);
-        final double goalNodeLat = 
-            getNodeCoordinate(goalNodeInternal, propertyKeyLat);
-        final double goalNodeLon = 
-            getNodeCoordinate(goalNodeInternal, propertyKeyLon);
-
-        final double initialHeuristic = 
-            computeHeuristic(startNodeLat,
-                startNodeLon,
-                goalNodeLat,
-                goalNodeLon);
-
-        gCosts.put(startNodeInternal, 0.0);
-        fCosts.put(startNodeInternal, initialHeuristic);
-        openNodes.add(startNodeInternal, 0.0);
-
-        run(goalNodeInternal,
-            propertyKeyLat,
-            propertyKeyLon,
-            direction);
-
-        if (path.containsKey(goalNodeInternal)) {
-            totalCost = gCosts.get(goalNodeInternal);
-            int node = goalNodeInternal;
-            while (node != PATH_END) {
-                shortestPath.addFirst(node);
-                node = path.getOrDefault(node, PATH_END);
-            }
-        }
-        return this;
-    }
-    
-    private void run(
-        final int goalNodeId,
-        final String propertyKeyLat,
-        final String propertyKeyLon,
-        final Direction direction) {
-
-        final double goalLat = 
-            getNodeCoordinate(goalNodeId, propertyKeyLat);
-        final double goalLon =
-            getNodeCoordinate(goalNodeId, propertyKeyLon);
-
-        while (!openNodes.isEmpty() && running()) {
-            int currentNodeId = openNodes.pop();
-            if (currentNodeId == goalNodeId) {
-                return;
-            }
-
-            closedNodes.put(currentNodeId);
-
-            double currentNodeCost = 
-                this.gCosts.getOrDefault(
-                    currentNodeId, 
-                    Double.MAX_VALUE);
-
-            graph.forEachRelationship(
-                currentNodeId,
-                direction,
-                (source, target, relationshipId, weight) -> {
-                    double neighbourLat = 
-                        getNodeCoordinate(target, propertyKeyLat);
-                    double neighbourLon = 
-                        getNodeCoordinate(target, propertyKeyLon);
-                    double heuristic = 
-                        computeHeuristic(
-                            neighbourLat, 
-                            neighbourLon, 
-                            goalLat,
-                            goalLon);
-
-                    updateCosts(
-                        source,
-                        target,
-                        weight + currentNodeCost,
-                        heuristic);
-
-                    if (!closedNodes.contains(target)) {
-                        openNodes.add(target, 0);
-                    }
-                    return true;
-                });
-
-            progressLogger.logProgress(
-                (double) currentNodeId / (nodeCount - 1));
-        }
-    }
-    
-    private double computeHeuristic(
-        final double lat1,
-        final double lon1,
-        final double lat2,
-        final double lon2) {
-
-        final int earthRadius = 6371;
-        final double kmToNM = 0.539957;
-        final double latDistance = Math.toRadians(lat2 - lat1);
-        final double lonDistance = Math.toRadians(lon2 - lon1);
-        final double a = Math.sin(latDistance / 2)
-            * Math.sin(latDistance / 2)
-            + Math.cos(Math.toRadians(lat1))
-            * Math.cos(Math.toRadians(lat2))
-            * Math.sin(lonDistance / 2)
-            * Math.sin(lonDistance / 2);
-        final double c = 2
-            * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
-        final double distance = earthRadius * c * kmToNM;
-        return distance;
-    }
-    
-    private double getNodeCoordinate(
-        final int nodeId,
-        final String coordinateType) {
-
-        final long neo4jId = graph.toOriginalNodeId(nodeId);
-        final Node node = dbService.getNodeById(neo4jId);
-        return (double) node.getProperty(coordinateType);
-    }
-    
-    private void updateCosts(
-        final int source, 
-        final int target, 
-        final double newCost,
-        final double heuristic) {
-
-        final double oldCost = 
-            gCosts.getOrDefault(target, Double.MAX_VALUE);
-
-        if (newCost < oldCost) {
-            gCosts.put(target, newCost);
-            fCosts.put(target, newCost + heuristic);
-            path.put(target, source);
-        }
-    }
-    
-    private void reset() {
-        closedNodes.clear();
-        openNodes.clear();
-        gCosts.clear();
-        fCosts.clear();
-        path.clear();
-        shortestPath.clear();
-        totalCost = NO_PATH_FOUND;
-    }
-    
-    public Stream<Result> resultStream() {
-        return StreamSupport.stream(
-            shortestPath.spliterator(), false)
-                .map(cursor -> new Result(
-                    graph.toOriginalNodeId(cursor.value),
-                    gCosts.get(cursor.value)));
-    }
-
-    public IntArrayDeque getFinalPath() {
-        return shortestPath;
-    }
-    
-    public double getTotalCost() {
-        return totalCost;
-    }
-
-    public int getPathLength() {
-        return shortestPath.size();
-    }
-    
-    @Override
-    public ShortestPathAStar me() {
-        return this;
-    }
-
-    @Override
-    public ShortestPathAStar release() {
-        graph = null;
-        gCosts = null;
-        fCosts = null;
-        openNodes = null;
-        path = null;
-        shortestPath = null;
-        closedNodes = null;
-        return this;
-    }
-    
-    public static class Result {
-
-        /**
-         * the neo4j node id
-         */
-        public final Long nodeId;
-
-        /**
-         * cost to reach the node from startNode
-         */
-        public final Double cost;
-
-        public Result(Long nodeId, Double cost) {
-            this.nodeId = nodeId;
-            this.cost = cost;
-        }
-    }
-}
-
    - -

    The heuristic function is domain-specific. If chosen wisely, it can -significantly speed up the search. In our case, we achieved a 300x speedup, -enabling us to expand our search from 4,000 to 13,000 route points. The v3.4.0 of the -Neo4J graph algorithms shipped with the A* search algorithm.

    - -
    -

    by W. D. Sadeep Madurange

    -
    -
    -
    - -
    -
    -
    -

    © ASCIIMX - 2025

    -
    -
    -
    - - - - diff --git a/_site/archive/suckless-software/index.html b/_site/archive/suckless-software/index.html deleted file mode 100644 index 418f8ce..0000000 --- a/_site/archive/suckless-software/index.html +++ /dev/null @@ -1,142 +0,0 @@ - - - - - How I manage Suckless software packages - - - - - How I manage Suckless software packages - - - - - - - - - - - - - -
    -
    -
    -

    HOW I MANAGE SUCKLESS SOFTWARE PACKAGES

    -
    30 NOVEMBER 2025
    -
    -

    Since suckless software requires users to modify the -source code and recompile to customize, I need a way to maintain patches over -the long term while retaining the ability to upgrade the software as new -versions are released.

    - -

    Initial setup

    - -

    When using a suckless program, I usually begin by cloning the project and -setting the remote URL to push a copy of the source code with my patches to my -own git repository:

    - -
    git clone git://git.suckless.org/dwm
-git reset --hard <tag>
-git remote set-url --push origin git@git.asciimx.com:/repos/dwm
-
    - -

    This way, I can pull updates from the upstream project whenever I want, while -committing my changes to my own git repository. The git reset command aligns my -branch head with a stable release before applying patches or installing the -software.

    - -

    If all I want to do is reconfigure the software (e.g., change key bindings), -which is what I need most of the time, the recommended approach is to modify -the config.h file. If the config.h isn’t yet in the project, the following -command generates it from the defaults and compiles the software using make -clean <target> here <target> is the name of the application (e.g., dwm) -found in the Makefile. I modify the resulting config.h file and run make clean -install to install the software before committing and pushing my changes to my -git repo.

    - -

    dwm and slstatus

    - -

    Since dwm and slstatus are always running, make install will likely fail for -them. The operating system will prevent the installer from replacing running -executables with new ones. Hence, we must first stop the running instances of -these programs (Mod + Shift + q). Then, switch to a tty (Ctrl + Alt + F1), -log in, and change the directory to where dwm/slstatus is. We can run make -install to install the software and switch back to the graphical session -(Ctrl + Alt + F5).

    - -

    The key combinations for switching to the tty and back may differ across -systems. The ones listed above are for OpenBSD.

    - -

    Subsequent upgrades

    - -

    When suckless releases a new version, I run git pull --rebase to fetch the -upstream changes and rebase my patches on top of them. Because I tend to use -stable versions, I perform another interactive rebase to drop the commits -between the latest stable version tag and my patch before installing the -software.

    - -

    Commit log before upgrading:

    - -
    dt236  My patch.
-3fkdf  Version 6.5.
-
    - -

    Commit log after pulling:

    - -
    w467d  My patch.
-gh25g  A commit.
-g525g  Another commit.
-3fkdf  Version 6.6.
-vd425  Old commit.
-q12vu  Another old commit.
-3fkdf  Version 6.5.
-
    - -

    Commit log after the interactive rebase:

    - -
    h57jh  My patch.
-3fkdf  Version 6.6.
-vd425  Old commit.
-q12vu  Another old commit.
-3fkdf  Version 6.5.
-
    - -

    And finally, commit and push all the changes to my own git repository.

    - -
    -

    by W. D. Sadeep Madurange

    -
    -
    -
    - -
    -
    -
    -

    © ASCIIMX - 2025

    -
    -
    -
    - - - - diff --git a/_site/assets/css/main.css b/_site/assets/css/main.css index ef53733..5a777c0 100644 --- a/_site/assets/css/main.css +++ b/_site/assets/css/main.css @@ -72,10 +72,16 @@ td { width: 50%; } +#navlist +{ + list-style-type: none; + margin-left: 0 !important; +} + #navlist li { display: inline; - list-style-type: none; + list-style-type: none inside; padding-right: 20px; } @@ -94,9 +100,6 @@ td { } @media (min-width: 550px) { - #nav-container { - padding: 0; - } .post-container { padding: 0; } diff --git a/_site/assets/css/skeleton.css b/_site/assets/css/skeleton.css index 40c9bdc..90239a6 100644 --- a/_site/assets/css/skeleton.css +++ b/_site/assets/css/skeleton.css @@ -275,12 +275,13 @@ label > .label-body { /* Lists –––––––––––––––––––––––––––––––––––––––––––––––––– */ ul { - list-style: circle inside; } + list-style: circle outside; } ol { - list-style: decimal inside; } + list-style: decimal outside; } ol, ul { padding-left: 0; - margin-top: 0; } + margin-top: 0; + margin-left: 1em; } ul ul, ul ol, ol ol, diff --git a/_site/blog/arduino-due/connections.jpeg b/_site/blog/arduino-due/connections.jpeg new file mode 100644 index 0000000..081e6d4 Binary files /dev/null and b/_site/blog/arduino-due/connections.jpeg differ diff --git a/_site/blog/arduino-due/index.html b/_site/blog/arduino-due/index.html new file mode 100644 index 0000000..fee442f --- /dev/null +++ b/_site/blog/arduino-due/index.html @@ -0,0 +1,172 @@ + + + + + How to set up ATSAM3X8E microcontrollers for bare-metal programming in C + + + + + How to set up ATSAM3X8E microcontrollers for bare-metal programming in C + + + + + + + + + + + + + +
    +
    +
    +

    HOW TO SET UP ATSAM3X8E MICROCONTROLLERS FOR BARE-METAL PROGRAMMING IN C

    +
    05 OCTOBER 2024
    +
    +

    This article is a step-by-step guide for programming bare-metal ATSAM3X8E chips +found on Arduino Due boards. It also includes notes on the chip’s memory layout +relevant for writing linker scripts. The steps described in this article were +tested on an OpenBSD workstation.

    + +

    Toolchain

    + +

    To interact directly with a bare-metal ATSAM3X8E chips, we must bypass the +embedded bootloader. To do that, we need a hardware programmer capable of +communicating with the chip over the Serial Wire Debug (SWD) protocol. Since +the workstation we upload the program from presumably doesn’t speak SWD, the +hardware programmer acts as a SWD-USB adapter. The ST-LINK/V2 programmer fits this +bill.

    + +

    The OpenOCD on-chip debugger software supports +ATSAM3X8E chips. OpenOCD, on startup, runs a telnet server that we can connect to +to issue commands to the ATSAM3X8E chip. OpenOCD translates plain-text commands +into the binary sequences the chip understands, and sends them over the wire.

    + +

    Finally, we need the ARM GNU Compiler +Toolchain to compile C programs for the chip. The ARM GNU compiler +toolchain and OpenOCD, as a consequence of being free software, are available +on every conceivable platform, including OpenBSD.

    + +

    Electrical connections

    + +

    The following photos illustrate the electrical connections between the Arduino +Due, PC, and the ST-LINK/V2 programmer required to transfer a compiled program +from a PC to the MCU.

    + + + + + + +
    + Pinout +

    Wiring

    +     		+ Circuit +

    Arduino Due

    +
    + +

    Arduino Due exposes the ATSAM3X8E’s SWD interface via its DEBUG port. The +ST-LINK/v2 programmer connects to that to communicate with the chip.

    + +

    Uploading the program

    + +

    The source.tar.gz tarball at the end of this page contains a sample C program +(the classic LED blink program) with OpenOCD configuration and linker scripts. +First, use the following command to build it:

    + +
    $ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \
+    -nostartfiles \
+    -nostdlib \
+    -o a.elf main.c
+
    + +

    Then, open a telnet session with OpenOCD and issue the following sequence of +commands to configure the chip and upload the compiled program to it:

    + +
    $ openocd -f openocd-due.cfg
+$ telnet localhost 4444
+  > halt
+  > at91sam3 gpnvm show
+  > at91sam3 gpnvm set 1
+  > at91sam3 gpnvm show
+$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit"
+
    + +

    The first of the above commands starts OpenOCD. In the telnet session, the +first command halts the chip in preparation for receiving commands. Next, we +inspect the current GPNVM bit setting (more on this later). If the bit is unset +(the gpnvm show command returns 0), we set it to 1 and verify the update.

    + +

    The final command, issued from outside the telnet session, uploads the program +to the chip. Those are the bare minimum set of commands required to program the +chip. The AT91SAM3 flash driver section of the OpenOCD manual lists all +available commands for the ATSAM3X8E chip.

    + +

    GPNVM bits

    + +

    By design, ARM chips boot into address 0x00000. ATSAM3X8E’s memory consists of +a ROM and a dual-banked flash (flash0 and flash1), residing in different +locations of the chip’s address space. The GPNVM bits control which of them +maps to 0x00000. When GPNVM1 is cleared (the default), the chip boots from the ROM, +which contains Atmel’s SAM-BA bootloader.

    + +

    Conversely, when the GPNVM1 bit is 1 (and the GPNVM2 bit is 0), flash0 at +address 0x80000 maps to 0x00000. When both GPNVM bits are 0, flash1 maps to +0x00000. Since we place our program in flash0 in the linker script, we set the +GPNVM1 bit and leave the GPNVM2 bit unchanged to ensure the chip +executes our program instead of the embedded bootloader at startup.

    + +

    Linker script

    + +

    At a minimum, the linker script must place the vector table at the first +address of the flash. This is mandatory for ARM chips unless we relocate the +vector table using the VTOR register.

    + +

    The first entry of the vector table must be the stack pointer. The stack +pointer must be initializes to the highest memory location available to +accommodate the ATSAM3X8E’s descending stack.

    + +

    The second entry of the vector table must be the reset vector. In the reset +vector, we can perform tasks such as zeroing out memory and initializing +registers before passing control to the main program.

    + +

    Files: source.tar.gz

    +
    +

    by W. D. Sadeep Madurange

    +
    +
    +
    + +
    +
    +
    +

    © ASCIIMX - 2025

    +
    +
    +
    + + + + diff --git a/_site/blog/arduino-due/schematic.png b/_site/blog/arduino-due/schematic.png new file mode 100644 index 0000000..62ddadd Binary files /dev/null and b/_site/blog/arduino-due/schematic.png differ diff --git a/_site/blog/arduino-due/source.tar.gz b/_site/blog/arduino-due/source.tar.gz new file mode 100644 index 0000000..496567b Binary files /dev/null and b/_site/blog/arduino-due/source.tar.gz differ diff --git a/_site/blog/arduino-uno/3v3.Makefile b/_site/blog/arduino-uno/3v3.Makefile new file mode 100644 index 0000000..4ca89d4 --- /dev/null +++ b/_site/blog/arduino-uno/3v3.Makefile @@ -0,0 +1,46 @@ +CC = avr-gcc +MCU = atmega328p +PORT = /dev/cuaU0 +TARGET = app + +SRC = main.c +OBJ = $(SRC:.c=.o) + +CFLAGS = -std=gnu99 +CFLAGS += -Os +CFLAGS += -Wall +CFLAGS += -mmcu=$(MCU) +CFLAGS += -DBAUD=57600 +CFLAGS += -DF_CPU=8000000UL +CFLAGS += -ffunction-sections -fdata-sections + +LDFLAGS = -mmcu=$(MCU) +LDFLAGS += -Wl,--gc-sections + +HEX_FLAGS = -O ihex +HEX_FLAGS += -j .text -j .data + +AVRDUDE_FLAGS = -p $(MCU) +AVRDUDE_FLAGS += -c arduino +AVRDUDE_FLAGS += -b 57600 +AVRDUDE_FLAGS += -P $(PORT) +AVRDUDE_FLAGS += -D -U + +%.o: %.c + $(CC) $(CFLAGS) -c -o $@ $< + +elf: $(OBJ) + $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf + +hex: elf + avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex + +upload: hex + avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i + +.PHONY: clean + +clean: + rm -f *.o *.elf *.hex + + diff --git a/_site/blog/arduino-uno/Makefile b/_site/blog/arduino-uno/Makefile new file mode 100644 index 0000000..9db7b09 --- /dev/null +++ b/_site/blog/arduino-uno/Makefile @@ -0,0 +1,43 @@ +CC = avr-gcc +MCU = atmega328p +PORT = /dev/cuaU0 +TARGET = app + +SRC = main.c +OBJ = $(SRC:.c=.o) + +CFLAGS = -std=gnu99 +CFLAGS += -Os +CFLAGS += -Wall +CFLAGS += -mmcu=$(MCU) +CFLAGS += -DBAUD=115200 +CFLAGS += -DF_CPU=16000000UL +CFLAGS += -ffunction-sections -fdata-sections + +LDFLAGS = -mmcu=$(MCU) +LDFLAGS += -Wl,--gc-sections + +HEX_FLAGS = -O ihex +HEX_FLAGS += -j .text -j .data + +AVRDUDE_FLAGS = -p $(MCU) +AVRDUDE_FLAGS += -c arduino +AVRDUDE_FLAGS += -P $(PORT) +AVRDUDE_FLAGS += -D -U + +%.o: %.c + $(CC) $(CFLAGS) -c -o $@ $< + +elf: $(OBJ) + $(CC) $(LDFLAGS) $(OBJ) -o $(TARGET).elf + +hex: elf + avr-objcopy $(HEX_FLAGS) $(TARGET).elf $(TARGET).hex + +upload: hex + avrdude $(AVRDUDE_FLAGS) flash:w:$(TARGET).hex:i + +.PHONY: clean + +clean: + rm *.o *.elf *.hex diff --git a/_site/blog/arduino-uno/breadboard.jpeg b/_site/blog/arduino-uno/breadboard.jpeg new file mode 100644 index 0000000..bd74907 Binary files /dev/null and b/_site/blog/arduino-uno/breadboard.jpeg differ diff --git a/_site/blog/arduino-uno/index.html b/_site/blog/arduino-uno/index.html new file mode 100644 index 0000000..7c4a71b --- /dev/null +++ b/_site/blog/arduino-uno/index.html @@ -0,0 +1,139 @@ + + + + + How to configure ATmega328P microcontrollers to run at 3.3V and 5V + + + + + How to configure ATmega328P microcontrollers to run at 3.3V and 5V + + + + + + + + + + + + + +
    +
    +
    +

    HOW TO CONFIGURE ATMEGA328P MICROCONTROLLERS TO RUN AT 3.3V AND 5V

    +
    10 APRIL 2025
    +
    +

    This is a quick reference for wiring up ATmega328P ICs to run at 5V and 3.3V. +While the 5V configuration is common, the 3.3V configuration can be useful in +low-power applications and when interfacing with parts that themselves run at +3.3V. In this guide, the 5V setup is configured with a 16MHz crystal +oscillator, while the 3.3V configuration makes use of an 8MHz crystal +oscillator.

    + +

    The steps that follow refer to the following pinout.

    + + + + + + +
    + Pinout +

    Pinout

    +     		+ Circuit +

    Breadboard

    +
    + +

    5V-16MHz configuration

    + +

    Powering ATmega328P microcontrollers with 5V is the most common setup. This is +also how Arduino Uno boards are wired.

    + +

    In this configuration, the microcontroller’s pin 1 is connected to 5V via a +10kΩ resistor. Pins 9 and 10 are connected to a 16MHz crystal oscillator via +two 22pF capacitors connected to ground. The microcontroller is powered by +connecting pins 7, 20, and 21 to a 5V DC power supply. Lastly, pins 8 and 22 +are connected to ground. In addition to the these connections, which are +required, it’s a good idea to add 0.1μF decoupling capacitors between pins 7, +20, and 21 and ground.

    + +

    Here’s a sample Makefile for compiling C programs for ATmega328P +microcontrollers using avr-gcc/avrdude toolchain.

    + +

    3.3V-8MHz configuration

    + +

    Electrical connections for running an ATmega328P at 3.3V are identical to that +of the 5V circuit. The only differences are that all the 5V connections are +replaced with a 3.3V power source and a 8MHz crystal oscillator takes the place +of the 16MHz crystal.

    + +

    However, standard ATmega328P chips are preconfigured to run at 5V. To run one +at 3.3V, we must first modify its fuses that control characteristics like the +BOD level. If a bootloader that expects a 16MHz clock (e.g., Arduino +bootloader) is pre-installed on the ATmega328P, it must be swapped with one +that accepts an 8MHz clock. To accomplish that, we need an in-system programmer +(ISP).

    + +

    Fortunately, we can turn an ordinary Arduino Uno board into an ISP by uploading +the ‘ArduinoISP’ sketch found in the Arduino IDE. The ISP communicates with the +microcontroller using a Serial Peripheral Interface (SPI). So, connect the SPI +port of the ATmega328P to that of the Arduino Uno, and the Uno’s SS pin +to the ATmega328P’s RESET pin.

    + +

    Power up the the ATmega328P by connecting its VCC to a 5V supply (we +can use Arduino Uno’s 5V pin). From the Arduino IDE, select ‘ATmega328P (3.3V, +8MHz)’ for processor from the tools menu. Also from the tools menu, select +‘Arduino as ISP’ as programmer. Finally, upload the new bootloader by selecting +‘Burn Bootloader’ from the tools menu.

    + +

    The ATmega328P is now ready to run at 8MHz with a 3.3V power supply. You can +upload programs to the ATmega328P as you normally would using avrdude. +Here’s a sample Makefile with adjusted parameters (e.g., baud +rate) for an 8MHz clock.

    + +

    Remarks

    + +

    In both configurations, if you intend to use the ATmega328P’s analog-to-digital +converter with the internal 1.1V or AVcc voltage as reference, do +not connect AREF (pin 21) to Vcc. Refer to section 23.5.2 in the +datasheet for more information.

    + +
    +

    by W. D. Sadeep Madurange

    +
    +
    +
    + +
    +
    +
    +

    © ASCIIMX - 2025

    +
    +
    +
    + + + + diff --git a/_site/blog/arduino-uno/pinout.png b/_site/blog/arduino-uno/pinout.png new file mode 100644 index 0000000..59acfbc Binary files /dev/null and b/_site/blog/arduino-uno/pinout.png differ diff --git a/_site/blog/index.html b/_site/blog/index.html new file mode 100644 index 0000000..c213ee5 --- /dev/null +++ b/_site/blog/index.html @@ -0,0 +1,129 @@ + + + + + + + Blog + + + + + + + + + + + + +
    + +

    Blog

    + +
    + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
    + How I manage Suckless software packages + + + + +
    + Neo4J A* search + + + + +
    + MOSFETs as electronic switches + + + + +
    + How to configure ATmega328P microcontrollers to run at 3.3V and 5V + + + + +
    + How to set up ATSAM3X8E microcontrollers for bare-metal programming in C + + + + +
    +
    + + +
    +
    + +
    +
    +
    +

    © ASCIIMX - 2025

    +
    +
    +
    + + + + diff --git a/_site/blog/mosfet-switches/bjt.png b/_site/blog/mosfet-switches/bjt.png new file mode 100644 index 0000000..9858fa7 Binary files /dev/null and b/_site/blog/mosfet-switches/bjt.png differ diff --git a/_site/blog/mosfet-switches/index.html b/_site/blog/mosfet-switches/index.html new file mode 100644 index 0000000..ed63e0a --- /dev/null +++ b/_site/blog/mosfet-switches/index.html @@ -0,0 +1,173 @@ + + + + + MOSFETs as electronic switches + + + + + MOSFETs as electronic switches + + + + + + + + + + + + + +
    +
    +
    +

    MOSFETS AS ELECTRONIC SWITCHES

    +
    22 JUNE 2025
    +
    +

    Recently, I needed a low-power circuit for one of my battery-operated projects. +Much of the system’s power savings depended on its ability to electronically +switch off components, such as servos, that draw high levels of quiescent +currents. My search for a solution led me to MOSFETs, transistors capable of +controlling circuits operating at voltages far above their own.

    + +

    Acknowledgments

    + +

    This article is a summary of what I learnt about using MOSFETs as switches. +I’m not an electronics engineer, and this is not an authoritative guide. The +circuits in this post must be considered within the narrow context in which +I’ve used them. All credits for the schematics belong to Simon Fitch.

    + +

    Preamble

    + +

    For a typical MOSFET-based switch, we can connect a GPIO pin of a +microcontroller to the gate of a logic-level N-channel MOSFET placed on the low +side of the load and tie the gate and the drain pins of the MOSFET with a +pull-down resistor. This would work as long as the power supplies of the +microcontroller and the load don’t share a common ground. Things become more +complicated when they do (e.g., controlling power to a component driven by the +same microcontroller).

    + +

    In that scenario, the source potential visible to the load is the difference +between the gate and the threshold potentials of the MOSFET. For example, when +the gate and the threshold potentials are 3.3 V and 1.5 V, the potential the +load sees is 1.8 V. So, to use a low-side N-channel MOSFET, we need the gate +potential to be higher than the source potential, which may not always be +practical. The alternative would be a hide-side switch.

    + +

    P-channel high-side switch

    + +

    The following schematic shows how a high-side P-channel MOSFET (M1) could +switch power to a 6 V servo driven by a 3.3 V MCU.

    + +

    P-channel high-side switching circuit

    + +

    When the microcontroller outputs low, the M2 N-channel MOSFET stops conducting. +The R1 resistor pulls the gate of the M1 P-channel MOSFET up to +6 V, switching +the servo off. When the microcontroller outputs high on the GPIO pin, M2’s +source-drain connection starts conducting, causing M1’s gate potential to drop +to 0 V, which switches on power to the servo.

    + +

    N-channel high-side switch

    + +

    The P-channel high-side switch would be the typical architecture for our use +case. However, if we have access to a potential high enough to safely raise the +gate potential above the threshold such that their difference outputs the source +potential required to drive the load, we can switch on the high side using an +N-channel MOSFET:

    + +

    N-channel high-side switching circuit

    + +

    In the schematic, both M1 and M2 are N-channel MOSFETs. When the +microcontroller output is low, M2 stops conducting. This causes the M1’s gate +potential to rise above the threshold, turning the servo on. Conversely, a high +output on the GPIO line switches M2 on, which lowers M1’s gate potential. This +switches the servo off. The R2 pull-up resistor prevents the high impedance of +the output pins at power-up from switching the servo on.

    + +

    Both topologies require M2 to act as a level converter between circuits +containing the microcontroller and the servo, converting between 0 V and +6 V +or +9 V. M2 is a low-power signal converter carrying less than a milliamp of +current. The gate-source threshold voltage of M2 must be lower than the MCU’s +supply voltage. 2N7000, 2N7002, and BSS138 are popular choices for M2.

    + +

    The D1 flyback diodes used in the two topologies safeguard the MOSFET from +voltage spikes caused by inductive loads such as servos.

    + +

    A BJT alternative

    + +

    A Bipolar Junction Transistor (BJT) is a simpler, cheaper, and more widely +available type of transistor that can be used as a switch.

    + +

    BJT architecture

    + +

    In the schematic, when the MCU outputs high, Q2 starts conducting. Q2 amplifies +Q1’s base current. Unlike MOSFETs, which are voltage-driven, BJTs are driven by +base current. Resistors R3 and R4 must be chosen carefully to output the +desired base currents. “How to choose a +transistor as a switch” is an excellent guide on using BJTs as electronic +switches.

    + +

    Which topology to choose?

    + +

    The professional community appears to prefer MOSFETs over BJTs. MOSFETs are +more efficient when the switch is on. However, they are more challenging to +drive, especially with a 3.3 V MCU, due to the VGS potentials +required to achieve specified RDS(on) values (i.e., to turn them on +fully).

    + +

    N-channel MOSFETs have lower on-resistance values, making them more efficient +than P-channel ones. They are also cheaper. However, they are harder to drive +on the high side as their gate potential must be higher than the source +potential. This often requires extra circuitry such as MOSFET drivers.

    + +

    Further reading

    + + +
    +

    by W. D. Sadeep Madurange

    +
    +
    +
    + +
    +
    +
    +

    © ASCIIMX - 2025

    +
    +
    +
    + + + + diff --git a/_site/blog/mosfet-switches/n_high_side.png b/_site/blog/mosfet-switches/n_high_side.png new file mode 100644 index 0000000..c851768 Binary files /dev/null and b/_site/blog/mosfet-switches/n_high_side.png differ diff --git a/_site/blog/mosfet-switches/p_high_side.png b/_site/blog/mosfet-switches/p_high_side.png new file mode 100644 index 0000000..9f5397a Binary files /dev/null and b/_site/blog/mosfet-switches/p_high_side.png differ diff --git a/_site/blog/neo4j-a-star-search/index.html b/_site/blog/neo4j-a-star-search/index.html new file mode 100644 index 0000000..0d918c7 --- /dev/null +++ b/_site/blog/neo4j-a-star-search/index.html @@ -0,0 +1,371 @@ + + + + + Neo4J A* search + + + + + Neo4J A* search + + + + + + + + + + + + + +
    +
    +
    +

    NEO4J A* SEARCH

    +
    14 SEPTEMBER 2025
    +
    +

    Back in 2018, we used Neo4J graph database to track the +movement of marine vessels. We were interested in the shortest path a ship +could take through a network of about 13,000 route points. Algorithms based on +graph theory, such as A* search, provide optimal solutions to such problems. +In other words, the set of route points lends itself well to a model based on +graphs.

    + +

    A graph is a finite set of vertices, and a subset of vertex pairs (edges). +Edges can have weights. In the case of vessel tracking, the route points form +the vertices of a graph; the routes between them, the edges; and the distances +between them are the weights. For different reasons, people are interested in +minimizing (or maximizing) the weight of a path through a set of vertices. For +instance, we may want to find the shortest path between two ports.

    + +

    Given such a graph, an algorithm like Dijkstra’s search could compute the +shortest path between two vertices. In fact, this was the algorithm Neo4J +shipped with at the time. One drawback of Dijkstra’s algorithm is that it +computes all the shortest paths from the source to all other vertices before +terminating at the destination vertex. The exhaustive nature of this search +limited our search to about 4,000 route points.

    + +

    The following enhancement to Dijkstra’s search, also known as the A* search, +employs a heuristic to steer the search in the direction of the destination +more quickly. In the case of our network of vessels, which are on the earth’s +surface, spherical distance is a good candidate for a heuristic:

    + +
    package org.neo4j.graphalgo.impl;
+
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+import org.neo4j.graphalgo.api.Graph;
+import org.neo4j.graphalgo.core.utils.ProgressLogger;
+import org.neo4j.graphalgo.core.utils.queue.IntPriorityQueue;
+import org.neo4j.graphalgo.core.utils.queue.SharedIntPriorityQueue;
+import org.neo4j.graphalgo.core.utils.traverse.SimpleBitSet;
+import org.neo4j.graphdb.Direction;
+import org.neo4j.graphdb.Node;
+import org.neo4j.kernel.internal.GraphDatabaseAPI;
+
+import com.carrotsearch.hppc.IntArrayDeque;
+import com.carrotsearch.hppc.IntDoubleMap;
+import com.carrotsearch.hppc.IntDoubleScatterMap;
+import com.carrotsearch.hppc.IntIntMap;
+import com.carrotsearch.hppc.IntIntScatterMap;
+
+public class ShortestPathAStar extends Algorithm<ShortestPathAStar> {
+    
+    private final GraphDatabaseAPI dbService;
+    private static final int PATH_END = -1;
+    
+    private Graph graph;
+    private final int nodeCount;
+    private IntDoubleMap gCosts;
+    private IntDoubleMap fCosts;
+    private double totalCost;
+    private IntPriorityQueue openNodes;
+    private IntIntMap path;
+    private IntArrayDeque shortestPath;
+    private SimpleBitSet closedNodes;
+    private final ProgressLogger progressLogger;
+    
+    public static final double NO_PATH_FOUND = -1.0;
+    
+    public ShortestPathAStar(
+        final Graph graph,
+        final GraphDatabaseAPI dbService) {
+
+        this.graph = graph;
+        this.dbService = dbService;
+
+        nodeCount = Math.toIntExact(graph.nodeCount());
+        gCosts = new IntDoubleScatterMap(nodeCount);
+        fCosts = new IntDoubleScatterMap(nodeCount);
+        openNodes = SharedIntPriorityQueue.min(
+            nodeCount,
+            fCosts,
+            Double.MAX_VALUE);
+        path = new IntIntScatterMap(nodeCount);
+        closedNodes = new SimpleBitSet(nodeCount);
+        shortestPath = new IntArrayDeque();
+        progressLogger = getProgressLogger();
+    }
+    
+    public ShortestPathAStar compute(
+        final long startNode,
+        final long goalNode,
+        final String propertyKeyLat,
+        final String propertyKeyLon,
+        final Direction direction) {
+
+        reset();
+
+        final int startNodeInternal = 
+            graph.toMappedNodeId(startNode);
+        final double startNodeLat =
+            getNodeCoordinate(startNodeInternal, propertyKeyLat);
+        final double startNodeLon = 
+            getNodeCoordinate(startNodeInternal, propertyKeyLon);
+
+        final int goalNodeInternal =
+            graph.toMappedNodeId(goalNode);
+        final double goalNodeLat = 
+            getNodeCoordinate(goalNodeInternal, propertyKeyLat);
+        final double goalNodeLon = 
+            getNodeCoordinate(goalNodeInternal, propertyKeyLon);
+
+        final double initialHeuristic = 
+            computeHeuristic(startNodeLat,
+                startNodeLon,
+                goalNodeLat,
+                goalNodeLon);
+
+        gCosts.put(startNodeInternal, 0.0);
+        fCosts.put(startNodeInternal, initialHeuristic);
+        openNodes.add(startNodeInternal, 0.0);
+
+        run(goalNodeInternal,
+            propertyKeyLat,
+            propertyKeyLon,
+            direction);
+
+        if (path.containsKey(goalNodeInternal)) {
+            totalCost = gCosts.get(goalNodeInternal);
+            int node = goalNodeInternal;
+            while (node != PATH_END) {
+                shortestPath.addFirst(node);
+                node = path.getOrDefault(node, PATH_END);
+            }
+        }
+        return this;
+    }
+    
+    private void run(
+        final int goalNodeId,
+        final String propertyKeyLat,
+        final String propertyKeyLon,
+        final Direction direction) {
+
+        final double goalLat = 
+            getNodeCoordinate(goalNodeId, propertyKeyLat);
+        final double goalLon =
+            getNodeCoordinate(goalNodeId, propertyKeyLon);
+
+        while (!openNodes.isEmpty() && running()) {
+            int currentNodeId = openNodes.pop();
+            if (currentNodeId == goalNodeId) {
+                return;
+            }
+
+            closedNodes.put(currentNodeId);
+
+            double currentNodeCost = 
+                this.gCosts.getOrDefault(
+                    currentNodeId, 
+                    Double.MAX_VALUE);
+
+            graph.forEachRelationship(
+                currentNodeId,
+                direction,
+                (source, target, relationshipId, weight) -> {
+                    double neighbourLat = 
+                        getNodeCoordinate(target, propertyKeyLat);
+                    double neighbourLon = 
+                        getNodeCoordinate(target, propertyKeyLon);
+                    double heuristic = 
+                        computeHeuristic(
+                            neighbourLat, 
+                            neighbourLon, 
+                            goalLat,
+                            goalLon);
+
+                    updateCosts(
+                        source,
+                        target,
+                        weight + currentNodeCost,
+                        heuristic);
+
+                    if (!closedNodes.contains(target)) {
+                        openNodes.add(target, 0);
+                    }
+                    return true;
+                });
+
+            progressLogger.logProgress(
+                (double) currentNodeId / (nodeCount - 1));
+        }
+    }
+    
+    private double computeHeuristic(
+        final double lat1,
+        final double lon1,
+        final double lat2,
+        final double lon2) {
+
+        final int earthRadius = 6371;
+        final double kmToNM = 0.539957;
+        final double latDistance = Math.toRadians(lat2 - lat1);
+        final double lonDistance = Math.toRadians(lon2 - lon1);
+        final double a = Math.sin(latDistance / 2)
+            * Math.sin(latDistance / 2)
+            + Math.cos(Math.toRadians(lat1))
+            * Math.cos(Math.toRadians(lat2))
+            * Math.sin(lonDistance / 2)
+            * Math.sin(lonDistance / 2);
+        final double c = 2
+            * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
+        final double distance = earthRadius * c * kmToNM;
+        return distance;
+    }
+    
+    private double getNodeCoordinate(
+        final int nodeId,
+        final String coordinateType) {
+
+        final long neo4jId = graph.toOriginalNodeId(nodeId);
+        final Node node = dbService.getNodeById(neo4jId);
+        return (double) node.getProperty(coordinateType);
+    }
+    
+    private void updateCosts(
+        final int source, 
+        final int target, 
+        final double newCost,
+        final double heuristic) {
+
+        final double oldCost = 
+            gCosts.getOrDefault(target, Double.MAX_VALUE);
+
+        if (newCost < oldCost) {
+            gCosts.put(target, newCost);
+            fCosts.put(target, newCost + heuristic);
+            path.put(target, source);
+        }
+    }
+    
+    private void reset() {
+        closedNodes.clear();
+        openNodes.clear();
+        gCosts.clear();
+        fCosts.clear();
+        path.clear();
+        shortestPath.clear();
+        totalCost = NO_PATH_FOUND;
+    }
+    
+    public Stream<Result> resultStream() {
+        return StreamSupport.stream(
+            shortestPath.spliterator(), false)
+                .map(cursor -> new Result(
+                    graph.toOriginalNodeId(cursor.value),
+                    gCosts.get(cursor.value)));
+    }
+
+    public IntArrayDeque getFinalPath() {
+        return shortestPath;
+    }
+    
+    public double getTotalCost() {
+        return totalCost;
+    }
+
+    public int getPathLength() {
+        return shortestPath.size();
+    }
+    
+    @Override
+    public ShortestPathAStar me() {
+        return this;
+    }
+
+    @Override
+    public ShortestPathAStar release() {
+        graph = null;
+        gCosts = null;
+        fCosts = null;
+        openNodes = null;
+        path = null;
+        shortestPath = null;
+        closedNodes = null;
+        return this;
+    }
+    
+    public static class Result {
+
+        /**
+         * the neo4j node id
+         */
+        public final Long nodeId;
+
+        /**
+         * cost to reach the node from startNode
+         */
+        public final Double cost;
+
+        public Result(Long nodeId, Double cost) {
+            this.nodeId = nodeId;
+            this.cost = cost;
+        }
+    }
+}
+
    + +

    The heuristic function is domain-specific. If chosen wisely, it can +significantly speed up the search. In our case, we achieved a 300x speedup, +enabling us to expand our search from 4,000 to 13,000 route points. The v3.4.0 of the +Neo4J graph algorithms shipped with the A* search algorithm.

    + +
    +

    by W. D. Sadeep Madurange

    +
    +
    +
    + +
    +
    +
    +

    © ASCIIMX - 2025

    +
    +
    +
    + + + + diff --git a/_site/blog/suckless-software/index.html b/_site/blog/suckless-software/index.html new file mode 100644 index 0000000..ea91072 --- /dev/null +++ b/_site/blog/suckless-software/index.html @@ -0,0 +1,142 @@ + + + + + How I manage Suckless software packages + + + + + How I manage Suckless software packages + + + + + + + + + + + + + +
    +
    +
    +

    HOW I MANAGE SUCKLESS SOFTWARE PACKAGES

    +
    30 NOVEMBER 2025
    +
    +

    Since suckless software requires users to modify the +source code and recompile to customize, I need a way to maintain patches over +the long term while retaining the ability to upgrade the software as new +versions are released.

    + +

    Initial setup

    + +

    When using a suckless program, I usually begin by cloning the project and +setting the remote URL to push a copy of the source code with my patches to my +own git repository:

    + +
    git clone git://git.suckless.org/dwm
+git reset --hard <tag>
+git remote set-url --push origin git@git.asciimx.com:/repos/dwm
+
    + +

    This way, I can pull updates from the upstream project whenever I want, while +committing my changes to my own git repository. The git reset command aligns my +branch head with a stable release before applying patches or installing the +software.

    + +

    If all I want to do is reconfigure the software (e.g., change key bindings), +which is what I need most of the time, the recommended approach is to modify +the config.h file. If the config.h isn’t yet in the project, the following +command generates it from the defaults and compiles the software using make +clean <target> here <target> is the name of the application (e.g., dwm) +found in the Makefile. I modify the resulting config.h file and run make clean +install to install the software before committing and pushing my changes to my +git repo.

    + +

    dwm and slstatus

    + +

    Since dwm and slstatus are always running, make install will likely fail for +them. The operating system will prevent the installer from replacing running +executables with new ones. Hence, we must first stop the running instances of +these programs (Mod + Shift + q). Then, switch to a tty (Ctrl + Alt + F1), +log in, and change the directory to where dwm/slstatus is. We can run make +install to install the software and switch back to the graphical session +(Ctrl + Alt + F5).

    + +

    The key combinations for switching to the tty and back may differ across +systems. The ones listed above are for OpenBSD.

    + +

    Subsequent upgrades

    + +

    When suckless releases a new version, I run git pull --rebase to fetch the +upstream changes and rebase my patches on top of them. Because I tend to use +stable versions, I perform another interactive rebase to drop the commits +between the latest stable version tag and my patch before installing the +software.

    + +

    Commit log before upgrading:

    + +
    dt236  My patch.
+3fkdf  Version 6.5.
+
    + +

    Commit log after pulling:

    + +
    w467d  My patch.
+gh25g  A commit.
+g525g  Another commit.
+3fkdf  Version 6.6.
+vd425  Old commit.
+q12vu  Another old commit.
+3fkdf  Version 6.5.
+
    + +

    Commit log after the interactive rebase:

    + +
    h57jh  My patch.
+3fkdf  Version 6.6.
+vd425  Old commit.
+q12vu  Another old commit.
+3fkdf  Version 6.5.
+
    + +

    And finally, commit and push all the changes to my own git repository.

    + +
    +

    by W. D. Sadeep Madurange

    +
    +
    +
    + +
    +
    +
    +

    © ASCIIMX - 2025

    +
    +
    +
    + + + + diff --git a/_site/feed.xml b/_site/feed.xml index 450f186..8574cb7 100644 --- a/_site/feed.xml +++ b/_site/feed.xml @@ -1 +1 @@ -Jekyll2025-12-08T17:12:03+08:00/feed.xmlASCIIMX | ArchiveW. D. Sadeep MadurangeHow I manage Suckless software packages2025-11-30T00:00:00+08:002025-11-30T00:00:00+08:00/archive/suckless-softwareW. D. Sadeep MadurangeNeo4J A* search2025-09-14T00:00:00+08:002025-09-14T00:00:00+08:00/archive/neo4j-a-star-searchW. D. Sadeep MadurangeMOSFETs as electronic switches2025-06-22T00:00:00+08:002025-06-22T00:00:00+08:00/archive/mosfet-switchesW. D. Sadeep MadurangeHow to configure ATmega328P microcontrollers to run at 3.3V and 5V2025-04-10T00:00:00+08:002025-04-10T00:00:00+08:00/archive/arduino-unoW. D. Sadeep MadurangeHow to set up ATSAM3X8E microcontrollers for bare-metal programming in C2024-10-05T00:00:00+08:002024-10-05T00:00:00+08:00/archive/arduino-dueW. D. Sadeep Madurange \ No newline at end of file +Jekyll2025-12-08T21:04:23+08:00/feed.xmlASCIIMX | BlogW. D. Sadeep MadurangeHow I manage Suckless software packages2025-11-30T00:00:00+08:002025-11-30T00:00:00+08:00/blog/suckless-softwareW. D. Sadeep MadurangeNeo4J A* search2025-09-14T00:00:00+08:002025-09-14T00:00:00+08:00/blog/neo4j-a-star-searchW. D. Sadeep MadurangeMOSFETs as electronic switches2025-06-22T00:00:00+08:002025-06-22T00:00:00+08:00/blog/mosfet-switchesW. D. Sadeep MadurangeHow to configure ATmega328P microcontrollers to run at 3.3V and 5V2025-04-10T00:00:00+08:002025-04-10T00:00:00+08:00/blog/arduino-unoW. D. Sadeep MadurangeHow to set up ATSAM3X8E microcontrollers for bare-metal programming in C2024-10-05T00:00:00+08:002024-10-05T00:00:00+08:00/blog/arduino-dueW. D. Sadeep Madurange \ No newline at end of file diff --git a/_site/index.html b/_site/index.html index 45e440f..6d65535 100644 --- a/_site/index.html +++ b/_site/index.html @@ -20,7 +20,7 @@ hme
  • - blg + blg
  • poc @@ -56,7 +56,7 @@ - How I manage Suckless software packages + How I manage Suckless software packages @@ -69,7 +69,7 @@ - Neo4J A* search + Neo4J A* search @@ -82,7 +82,7 @@ - MOSFETs as electronic switches + MOSFETs as electronic switches @@ -95,7 +95,7 @@ - How to configure ATmega328P microcontrollers to run at 3.3V and 5V + How to configure ATmega328P microcontrollers to run at 3.3V and 5V @@ -108,7 +108,7 @@ - How to set up ATSAM3X8E microcontrollers for bare-metal programming in C + How to set up ATSAM3X8E microcontrollers for bare-metal programming in C diff --git a/_site/posts.xml b/_site/posts.xml index 04b0a19..6a3103c 100644 --- a/_site/posts.xml +++ b/_site/posts.xml @@ -1 +1 @@ -Jekyll2025-12-08T17:12:03+08:00/posts.xmlASCIIMXW. D. Sadeep Madurange \ No newline at end of file +Jekyll2025-12-08T21:04:23+08:00/posts.xmlASCIIMXW. D. Sadeep Madurange \ No newline at end of file diff --git a/_site/projects/bumblebee/index.html b/_site/projects/bumblebee/index.html index d5c573d..7004f2e 100644 --- a/_site/projects/bumblebee/index.html +++ b/_site/projects/bumblebee/index.html @@ -24,7 +24,7 @@ hme
  • - blg + blg
  • poc diff --git a/_site/projects/e-reader/index.html b/_site/projects/e-reader/index.html index 47edd81..5a81e2b 100644 --- a/_site/projects/e-reader/index.html +++ b/_site/projects/e-reader/index.html @@ -24,7 +24,7 @@ hme
  • - blg + blg
  • poc diff --git a/_site/projects/etlas/index.html b/_site/projects/etlas/index.html index 897e162..f8f539f 100644 --- a/_site/projects/etlas/index.html +++ b/_site/projects/etlas/index.html @@ -24,7 +24,7 @@ hme
  • - blg + blg
  • poc diff --git a/_site/projects/fpm-door-lock/index.html b/_site/projects/fpm-door-lock/index.html index aa05298..5170201 100644 --- a/_site/projects/fpm-door-lock/index.html +++ b/_site/projects/fpm-door-lock/index.html @@ -24,7 +24,7 @@ hme
  • - blg + blg
  • poc diff --git a/_site/projects/index.html b/_site/projects/index.html index f23333a..924dbad 100644 --- a/_site/projects/index.html +++ b/_site/projects/index.html @@ -20,7 +20,7 @@ hme
  • - blg + blg
  • poc diff --git a/_site/projects/matrix-digital-rain/index.html b/_site/projects/matrix-digital-rain/index.html index 7f4b037..666456b 100644 --- a/_site/projects/matrix-digital-rain/index.html +++ b/_site/projects/matrix-digital-rain/index.html @@ -24,7 +24,7 @@ hme
  • - blg + blg
  • poc diff --git a/_site/projects/my-first-pcb/index.html b/_site/projects/my-first-pcb/index.html index 75dab1e..412bfcf 100644 --- a/_site/projects/my-first-pcb/index.html +++ b/_site/projects/my-first-pcb/index.html @@ -24,7 +24,7 @@ hme
  • - blg + blg
  • poc diff --git a/_site/sitemap.xml b/_site/sitemap.xml index 669f6b7..1b23cd3 100644 --- a/_site/sitemap.xml +++ b/_site/sitemap.xml @@ -1,23 +1,23 @@ -/archive/arduino-due/ +/blog/arduino-due/ 2024-10-05T00:00:00+08:00 -/archive/arduino-uno/ +/blog/arduino-uno/ 2025-04-10T00:00:00+08:00 -/archive/mosfet-switches/ +/blog/mosfet-switches/ 2025-06-22T00:00:00+08:00 -/archive/neo4j-a-star-search/ +/blog/neo4j-a-star-search/ 2025-09-14T00:00:00+08:00 -/archive/suckless-software/ +/blog/suckless-software/ 2025-11-30T00:00:00+08:00 @@ -48,7 +48,7 @@ /about/ -/archive/ +/blog/ / diff --git a/about.html b/about.html index 0032a72..3f71d59 100644 --- a/about.html +++ b/about.html @@ -11,18 +11,20 @@ title: About

    - Site structure:
    -

      -
    • hme: Home page, listing latest articles.
      • -
    • blg: Notes and tutorials about software and embedded systems.
      • -
    • poc: Projects, prototypes, and experiments.
      • -
    • abt: Site information.
      • -
    • rss: RSS (Atom) feed.
      • -
    Email: sadeep@asciimx.com [GPG]

    +

    Navigation

    + +
      +
    • hme: Home page, listing latest articles.
      • +
    • blg: Notes and tutorials about software and embedded systems.
      • +
    • poc: Projects, prototypes, and experiments.
      • +
    • abt: Site information.
      • +
    • rss: RSS (atom) feed.
      • +
    +

    About site

    diff --git a/archive.html b/archive.html deleted file mode 100644 index c33bbce..0000000 --- a/archive.html +++ /dev/null @@ -1,13 +0,0 @@ ---- -title: Archive -layout: default ---- - - -

    - -

    Archive

    - - {% include archive.html limit="50" %} - -
    diff --git a/assets/css/main.css b/assets/css/main.css index ef53733..5a777c0 100644 --- a/assets/css/main.css +++ b/assets/css/main.css @@ -72,10 +72,16 @@ td { width: 50%; } +#navlist +{ + list-style-type: none; + margin-left: 0 !important; +} + #navlist li { display: inline; - list-style-type: none; + list-style-type: none inside; padding-right: 20px; } @@ -94,9 +100,6 @@ td { } @media (min-width: 550px) { - #nav-container { - padding: 0; - } .post-container { padding: 0; } diff --git a/assets/css/skeleton.css b/assets/css/skeleton.css index 40c9bdc..90239a6 100644 --- a/assets/css/skeleton.css +++ b/assets/css/skeleton.css @@ -275,12 +275,13 @@ label > .label-body { /* Lists –––––––––––––––––––––––––––––––––––––––––––––––––– */ ul { - list-style: circle inside; } + list-style: circle outside; } ol { - list-style: decimal inside; } + list-style: decimal outside; } ol, ul { padding-left: 0; - margin-top: 0; } + margin-top: 0; + margin-left: 1em; } ul ul, ul ol, ol ol, diff --git a/blog.html b/blog.html new file mode 100644 index 0000000..481f255 --- /dev/null +++ b/blog.html @@ -0,0 +1,13 @@ +--- +title: Blog +layout: default +--- + + +
    + +

    Blog

    + + {% include latest.html limit="50" %} + +
    diff --git a/index.html b/index.html index f6c8a95..1a777d9 100644 --- a/index.html +++ b/index.html @@ -17,6 +17,6 @@ title: ASCIIMX

    - {% include archive.html limit="10" %} + {% include latest.html limit="10" %} -- cgit v1.2.3