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| author | Sadeep Madurange <sadeep@asciimx.com> | 2026-01-04 17:57:39 +0800 |
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| committer | Sadeep Madurange <sadeep@asciimx.com> | 2026-01-04 17:57:39 +0800 |
| commit | 1a4a6cb6d2aa2c8512e9637dc5dd95997321c444 (patch) | |
| tree | 7b6b9e514b48d64dd811b75c680c1268b532aec6 /_log | |
| parent | 16fe66dd83cbffa18af31676a380660ebce4e827 (diff) | |
| download | www-1a4a6cb6d2aa2c8512e9637dc5dd95997321c444.tar.gz | |
Fix the search engine post.
Diffstat (limited to '_log')
61 files changed, 93 insertions, 1581 deletions
diff --git a/_log/_site/arduino-due.html b/_log/_site/arduino-due.html deleted file mode 100644 index 172ee1a..0000000 --- a/_log/_site/arduino-due.html +++ /dev/null @@ -1,109 +0,0 @@ -<p>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.</p> - -<h2 id="toolchain">Toolchain</h2> - -<p>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 <a href="https://www.st.com/en/development-tools/st-link-v2.html" class="external" target="_blank" rel="noopener noreferrer">ST-LINK/V2</a> programmer fits this -bill.</p> - -<p>The <a href="https://openocd.org/" class="external" target="_blank" rel="noopener noreferrer">OpenOCD</a> 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.</p> - -<p>Finally, we need the <a href="https://developer.arm.com/Tools%20and%20Software/GNU%20Toolchain" class="external" target="_blank" rel="noopener noreferrer">ARM GNU Compiler -Toolchain</a> 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.</p> - -<h2 id="electrical-connections">Electrical connections</h2> - -<p>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.</p> - -<table style="border: none; width: 100%;"> - <tr style="border: none;"> - <td style="border: none; width: 50%; vertical-align: top; background-color: transparent;"> - <img src="schematic.png" alt="Pinout" style="width: 100%" /> - <p style="text-align: center;">Wiring</p> - </td> - <td style="border: none; width: 50%; vertical-align: top; background-color: transparent;"> - <img src="connections.jpeg" alt="Circuit" style="width: 100%" /> - <p style="text-align: center;">Arduino Due</p> - </td> - </tr> -</table> - -<p>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.</p> - -<h2 id="uploading-the-program">Uploading the program</h2> - -<p>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:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \ - -nostartfiles \ - -nostdlib \ - -o a.elf main.c -</code></pre></div></div> - -<p>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:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ 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" -</code></pre></div></div> - -<p>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.</p> - -<p>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.</p> - -<h2 id="gpnvm-bits">GPNVM bits</h2> - -<p>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.</p> - -<p>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.</p> - -<h2 id="linker-script">Linker script</h2> - -<p>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.</p> - -<p>The first entry of the vector table must be the stack pointer. The stack -pointer must be initialized to the highest memory location available to -accommodate the ATSAM3X8E’s descending stack.</p> - -<p>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.</p> - -<p>Files: <a href="source.tar.gz">source.tar.gz</a></p> diff --git a/_log/_site/arduino-due/connections.jpeg b/_log/_site/arduino-due/connections.jpeg Binary files differdeleted file mode 100644 index 081e6d4..0000000 --- a/_log/_site/arduino-due/connections.jpeg +++ /dev/null diff --git a/_log/_site/arduino-due/schematic.png b/_log/_site/arduino-due/schematic.png Binary files differdeleted file mode 100644 index 62ddadd..0000000 --- a/_log/_site/arduino-due/schematic.png +++ /dev/null diff --git a/_log/_site/arduino-due/source.tar.gz b/_log/_site/arduino-due/source.tar.gz Binary files differdeleted file mode 100644 index 496567b..0000000 --- a/_log/_site/arduino-due/source.tar.gz +++ /dev/null diff --git a/_log/_site/arduino-uno.html b/_log/_site/arduino-uno.html deleted file mode 100644 index d8ffac4..0000000 --- a/_log/_site/arduino-uno.html +++ /dev/null @@ -1,76 +0,0 @@ -<p>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.</p> - -<p>The steps that follow refer to the following pinout.</p> - -<table style="border: none; width: 100%;"> - <tr style="border: none;"> - <td style="border: none; width: 50%; vertical-align: top;"> - <img src="pinout.png" alt="Pinout" style="width: 100%" /> - <p style="text-align: center;">Pinout</p> - </td> - <td style="border: none; width: 50%; vertical-align: top;"> - <img src="breadboard.jpeg" alt="Circuit" style="width: 100%" /> - <p style="text-align: center;">Breadboard</p> - </td> - </tr> -</table> - -<h2 id="5v-16mhz-configuration">5V-16MHz configuration</h2> - -<p>Powering ATmega328P microcontrollers with 5V is the most common setup. This is -also how Arduino Uno boards are wired.</p> - -<p>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.</p> - -<p><a href="Makefile">Here’s</a> a sample Makefile for compiling C programs for ATmega328P -microcontrollers using avr-gcc/avrdude toolchain.</p> - -<h2 id="33v-8mhz-configuration">3.3V-8MHz configuration</h2> - -<p>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.</p> - -<p>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).</p> - -<p>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.</p> - -<p>Power up the the ATmega328P by connecting its V<sub>CC</sub> 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.</p> - -<p>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. -<a href="3v3.Makefile">Here’s</a> a sample Makefile with adjusted parameters (e.g., baud -rate) for an 8MHz clock.</p> - -<h2 id="remarks">Remarks</h2> - -<p>In both configurations, if you intend to use the ATmega328P’s analog-to-digital -converter with the internal 1.1V or AV<sub>cc</sub> voltage as reference, do -not connect AREF (pin 21) to V<sub>cc</sub>. Refer to section 23.5.2 in the -datasheet for more information.</p> - diff --git a/_log/_site/arduino-uno/3v3.Makefile b/_log/_site/arduino-uno/3v3.Makefile deleted file mode 100644 index 4ca89d4..0000000 --- a/_log/_site/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/_log/_site/arduino-uno/Makefile b/_log/_site/arduino-uno/Makefile deleted file mode 100644 index 9db7b09..0000000 --- a/_log/_site/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/_log/_site/arduino-uno/breadboard.jpeg b/_log/_site/arduino-uno/breadboard.jpeg Binary files differdeleted file mode 100644 index bd74907..0000000 --- a/_log/_site/arduino-uno/breadboard.jpeg +++ /dev/null diff --git a/_log/_site/arduino-uno/pinout.png b/_log/_site/arduino-uno/pinout.png Binary files differdeleted file mode 100644 index 59acfbc..0000000 --- a/_log/_site/arduino-uno/pinout.png +++ /dev/null diff --git a/_log/_site/bumblebee.html b/_log/_site/bumblebee.html deleted file mode 100644 index a466d0b..0000000 --- a/_log/_site/bumblebee.html +++ /dev/null @@ -1,40 +0,0 @@ -<p>Bumblebee is a tool I built for one of my employers to automate the generation -of web scraping scripts.</p> - -<video style="max-width:100%; margin-bottom: 10px" controls="" poster="poster.png"> - <source src="bee.mp4" type="video/mp4" /> -</video> - -<p>In 2024, we were tasked with collecting market data using various methods, -including scraping data from authorized websites for traders’ use.</p> - -<p>Manual authoring of such scripts took time. The scripts were often brittle due -to the complexity of the modern web, and they lacked optimizations such as -bypassing the UI and retrieving the data files directly when possible, which -would have significantly reduced our compute costs.</p> - -<p>To alleviate these challenges, I, with the help of a colleague, Andy Zhang, -built Bumblebee: a web browser powered by C# Windows Forms, Microsoft Edge <a src="https://developer.microsoft.com/en-us/microsoft-edge/webview2" class="external" target="_blank" rel="noopener noreferrer">WebView2</a>, and -the <a src="https://github.com/desjarlais/Scintilla.NET" class="external" toarget="_blank" rel="noopener noreferrer">Scintilla.NET</a> text editor.</p> - -<p>Bumblebee works by injecting a custom JavaScript program that intercepts -client-side events and sends them to Bumblebee for analysis. In addition to -front-end events, Bumblebee also captures internal browser events, which it -then interprets to generate code in real time. Note that we developed Bumblebee -before the advent of now-popular LLMs. Bumblebee supports dynamic websites, -pop-ups, developer tools, live manual override, event debouncing, and filtering -hidden elements and scripts.</p> - -<p>Before settling on a desktop application, we contemplated designing Bumblebee -as a browser extension. We chose the desktop app because extensions don’t offer -the deep, event-based control we needed. Besides, the company’s security -policy, which prohibited browser extensions, would have complicated the -deployment of an extension-based solution. My first prototype used a C# binding -of the Chromium project. WebView’s more intuitive API and its seamless -integration with Windows Forms led us to choose it over the Chromium wrapper.</p> - -<p>What began as a personal side project to improve my own workflow enabled us to -collectively improve the quality of our web scripts at a much larger scale. -Bumblebee predictably reduced the time we spent on authoring scripts from hours -to a few minutes.</p> - diff --git a/_log/_site/bumblebee/bee.mp4 b/_log/_site/bumblebee/bee.mp4 Binary files differdeleted file mode 100644 index 835600d..0000000 --- a/_log/_site/bumblebee/bee.mp4 +++ /dev/null diff --git a/_log/_site/bumblebee/poster.png b/_log/_site/bumblebee/poster.png Binary files differdeleted file mode 100644 index 6dc955e..0000000 --- a/_log/_site/bumblebee/poster.png +++ /dev/null diff --git a/_log/_site/bumblebee/thumb_sm.png b/_log/_site/bumblebee/thumb_sm.png Binary files differdeleted file mode 100644 index f7cfbf3..0000000 --- a/_log/_site/bumblebee/thumb_sm.png +++ /dev/null diff --git a/_log/_site/e-reader.html b/_log/_site/e-reader.html deleted file mode 100644 index f60c485..0000000 --- a/_log/_site/e-reader.html +++ /dev/null @@ -1,85 +0,0 @@ -<p>This project features an experimental e-reader powered by an ESP-WROOM-32 -development board and a 7.5-inch <a href="https://www.waveshare.com/" class="external" target="_blank" rel="noopener noreferrer">Waveshare</a> -e-paper display built with the intention of learning about e-paper displays.</p> - -<video style="max-width:100%;" controls="" poster="poster.png"> - <source src="ereader.mp4" type="video/mp4" /> -</video> - -<h2 id="introduction">Introduction</h2> - -<p>The prototype e-reader comprises an ESP32 microcontroller, an e-paper display -HAT, and three buttons: yellow, blue, and white for turning the page backwards, -forwards, and putting the device to sleep, respectively. The prototype does not -store books on the microcontroller. It streams books from a server over HTTP. -The e-reader employs RTC memory to record the reading progress between -sessions.</p> - -<p>The most formidable challenge when trying to build an e-reader with an ESP32 is -its limited memory and storage. My ESP-WROOM-32 has a total of 512KB of SRAM -and 4MB of flash memory, which the freeRTOS, ESP-IDF, and the e-reader -application must share. To put things into perspective, a Kindle Paperwhite has -at least 256MB of memory and 8GB of storage. That is 500x more memory than what -I’d have to work with.</p> - -<p>Despite its size, as microcontrollers go, ESP32 is a powerful system-on-a-chip -with a 160MHz dual-core processor and integrated WiFi. So, I thought it’d be -amusing to embrace the constraints and build my e-reader using a $5 MCU and the -power of C programming.</p> - -<h2 id="the-file-format">The file format</h2> - -<p>The file format dictates the complexity of the embedded software. So, I’ll -begin there. The e-reader works by downloading and rendering a rasterized -monochrome image of a page (a .ebm file).</p> - -<p>The EBM file contains a series of bitmaps, one for each page of the book. The -dimensions of each bitmap are equal to the size of the display. Each byte of -the bitmap encodes information for rendering eight pixels. For my display, -which has a resolution of 480x800, the bitmaps are laid out along 48KB -boundaries. This simple file format lends well to HTTP streaming, which is its -main advantage, as we will soon see.</p> - -<p>The pdftoebm.py script enclosed in the tarball at the end of the page converts -PDF documents to EBM files.</p> - -<h2 id="how-does-it-work">How does it work?</h2> - -<p>As the e-reader has no storage, it can’t store books locally. Instead, it -downloads pages of the EBM file over HTTP from the location pointed to by the -<code class="language-plaintext highlighter-rouge">EBM_ARCH_URL</code> setting in the Kconfig.projbuild file on demand. To read a -different book, we have to replace the old file with the new one or change the -<code class="language-plaintext highlighter-rouge">EBM_ARCH_URL</code> value. The latter requires us to recompile the embedded -software.</p> - -<p>Upon powering up, the e-reader checks the reading progress stored in the RTC -memory. It then downloads three pages (current, previous, and next) to a -circular buffer in DMA-capable memory. When the user turns a page by pressing a -button, one of the microprocessor’s two cores transfers it from the buffer to -the display over a Serial Peripheral Interface (SPI). The other downloads a new -page in the background. I used the ESP-IDF task API to schedule the two tasks -on different cores of the multicore processor to make the reader more -responsive.</p> - -<p>I designed the EBM format with HTTP streaming in mind. Since the pages are laid -out in the EBM file along predictable boundaries, the e-reader can request -pages by specifying the offset and the chunk size in the HTTP Range header. Any -web server will process this request without custom logic.</p> - -<h2 id="epilogue">Epilogue</h2> - -<p>My fascination with e-paper began back in 2017, when I was tasked with -installing a few displays in a car park. Having no idea how they worked, I -remember watching the languid screens refresh like a Muggle witnessing magic. -This project was born out of that enduring curiosity and love of e-paper -technology.</p> - -<p>Why did I go to the trouble of building a rudimentary e-reader when I could -easily buy a more capable commercial e-reader? First of all, it’s to prove to -myself that I can. More importantly, there’s a quiet satisfaction to reading on -hardware you built yourself. You are no longer the powerless observer watching -the magic happen from the sidelines. You become the wizard who makes the -invisible particles swirl into form by whispering C to them. There’s only one -way to experience that.</p> - -<p>Files: <a href="source.tar.gz">source.tar.gz</a></p> diff --git a/_log/_site/e-reader/circuit.svg b/_log/_site/e-reader/circuit.svg deleted file mode 100644 index fd7508b..0000000 --- a/_log/_site/e-reader/circuit.svg +++ /dev/null @@ -1,145 +0,0 @@ -<?xml version="1.0" encoding="utf-8"?> -<!-- Generator: Circuit Diagram, cdlibrary.dll 4.0.0.0 --> -<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> -<svg version="1.1" width="680" height="360" xmlns="http://www.w3.org/2000/svg"> - <line x1="360" y1="130" x2="360" y2="330" style="stroke:rgb(0, 0, 0);stroke-linecap:square;stroke-width:2" /> - <line x1="70" y1="330" x2="360" y2="330" style="stroke:rgb(0, 0, 0);stroke-linecap:square;stroke-width:2" /> - <line x1="70" y1="250" x2="70" y2="260" style="stroke:rgb(0, 0, 0);stroke-linecap:square;stroke-width:2" /> - <line x1="70" y1="260" x2="70" y2="275" style="stroke:rgb(0, 0, 0);stroke-linecap:square;stroke-width:2" /> - 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\ No newline at end of file diff --git a/_log/_site/e-reader/ereader.mp4 b/_log/_site/e-reader/ereader.mp4 Binary files differdeleted file mode 100644 index 89e05eb..0000000 --- a/_log/_site/e-reader/ereader.mp4 +++ /dev/null diff --git a/_log/_site/e-reader/poster.png b/_log/_site/e-reader/poster.png Binary files differdeleted file mode 100644 index 1e222d2..0000000 --- a/_log/_site/e-reader/poster.png +++ /dev/null diff --git a/_log/_site/e-reader/source.tar.gz b/_log/_site/e-reader/source.tar.gz Binary files differdeleted file mode 100644 index 3e343a7..0000000 --- a/_log/_site/e-reader/source.tar.gz +++ /dev/null diff --git a/_log/_site/e-reader/thumb_sm.png b/_log/_site/e-reader/thumb_sm.png Binary files differdeleted file mode 100644 index 7c971e8..0000000 --- a/_log/_site/e-reader/thumb_sm.png +++ /dev/null diff --git a/_log/_site/etlas.html b/_log/_site/etlas.html deleted file mode 100644 index 06e3ce7..0000000 --- a/_log/_site/etlas.html +++ /dev/null @@ -1,103 +0,0 @@ -<p>Etlas is a news, stock market, and weather tracker powered by an ESP32 NodeMCU -D1, featuring a 7.5-inch <a href="https://www.waveshare.com/" class="external" target="_blank" rel="noopener noreferrer">Waveshare</a> e-paper display and a -DHT22 sensor module.</p> - -<table style="border: none;"> - <tr style="border: none;"> - <td style="border: none;"><img src="dash.jpg" alt="front" style="width: 100%" /></td> - <td style="border: none;"><img src="pcb.jpg" alt="back" style="width: 100%" /></td> - </tr> -</table> - -<p>The top-left panel shows two weeks of end-of-day prices—the maximum the ESP32’s -SRAM can hold—from the Polygon.io API. The price feed is relayed through a -FastCGI-wrapped Flask app hosted on a VPS. This lets me configure stock symbols -in its application settings. The app cycles through them as requests come in -from the ESP32. Running the Flask app as a FastCGI process while exposing it -via httpd with htpasswd authentication keeps the server code simple and secure.</p> - -<p>The following diagram outlines the Etlas’s overall system architecture.</p> - -<p><img src="etlas_arch.png" alt="architecture" /></p> - -<p>The more prominent panel on the right of the display shows local and world news -from Channel NewsAsia. The MCU downloads and parses XML data from the RSS feed -directly before rendering it to the display. The character glyphs used are -stored as bitmaps in the sprites directory. I skipped the proxy for news to -avoid writing more server code, but in hindsight it limits the feeds Etlas can -handle. I will fix this in a future version.</p> - -<p>The middle and bottom right panels display the temperature and relative -humidity from the DHT22 sensor. The DHT22 uses pulse-width modulation to -transmit data to the host. The 26µs, 50µs, and 70µs pulses are too fast for the -ESP32 to measure reliably with standard APIs. Instead, the driver compares -relative pulse widths to differentiate zeros from ones:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>static inline int dht_await_pin_state(int state, int timeout) -{ - int t; - static const uint16_t delta = 1; - - for (t = 0; t < timeout; t += delta) { - ets_delay_us(delta); - if (gpio_get_level(DHT_PIN) == state) - return t; - } - return 0; -} - -static inline int dht_get_raw_data(unsigned char buf[DHT_DATA_LEN]) -{ - int rc; - unsigned char i, pwl, pwh; - - gpio_set_level(DHT_PIN, 0); - ets_delay_us(1100); - gpio_set_level(DHT_PIN, 1); - - if (!dht_await_pin_state(0, 40)) { - rc = 1; - xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); - return 0; - } - if (!dht_await_pin_state(1, 80)) { - rc = 2; - xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); - return 0; - } - if (!dht_await_pin_state(0, 80)) { - rc = 3; - xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); - return 0; - } - - for (i = 0; i < DHT_DATA_LEN; i++) { - if (!(pwl = dht_await_pin_state(1, 50))) { - rc = 4; - xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); - return 0; - } - if (!(pwh = dht_await_pin_state(0, 70))) { - rc = 5; - xQueueSend(dht_evt_queue, &rc, (TickType_t) 0); - return 0; - } - buf[i] = pwh > pwl; - } - return 1; -} -</code></pre></div></div> - -<p>I ported <a href="https://github.com/Fonger/ESP8266-RTOS-DHT" class="external" target="_blank" rel="noopener noreferrer">this</a> implementation from ESP8266 -to ESP32—all credit for the algorithm belongs to them.</p> - -<p>Etlas is a networked embedded system. All acquisition, processing, and -rendering of data are performed on the ESP32’s 160MHz microprocessor using less -than 512KB of SRAM. The embedded software that makes this possible is written -in C using ESP-IDF v5.2.1. The e-paper display driver is derived from Waveshare -<a href="https://github.com/waveshareteam/e-Paper" class="external" target="_blank" rel="noopener noreferrer">examples</a> for Arduino and STM32 -platforms.</p> - -<p>Etlas has been running reliably for over a year since August 2024.</p> - -<p>Files: <a href="source.tar.gz">source.tar.gz</a></p> diff --git a/_log/_site/etlas/circuit.svg b/_log/_site/etlas/circuit.svg deleted file mode 100644 index 6255045..0000000 --- a/_log/_site/etlas/circuit.svg +++ /dev/null @@ -1,105 +0,0 @@ -<?xml version="1.0" encoding="utf-8"?> -<!-- Generator: Circuit Diagram, cdlibrary.dll 4.0.0.0 --> -<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> -<svg version="1.1" width="700" height="300" xmlns="http://www.w3.org/2000/svg"> - <line x1="380" y1="220" x2="380" y2="280" style="stroke:rgb(0, 0, 0);stroke-linecap:square;stroke-width:2" /> - <line x1="340" y1="220" x2="550" y2="220" style="stroke:rgb(0, 0, 0);stroke-linecap:square;stroke-width:2" /> - 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\ No newline at end of file diff --git a/_log/_site/fpm-door-lock.html b/_log/_site/fpm-door-lock.html deleted file mode 100644 index 820af3f..0000000 --- a/_log/_site/fpm-door-lock.html +++ /dev/null @@ -1,105 +0,0 @@ -<p>This project features a fingerprint door lock powered by an ATmega328P -microcontroller.</p> - -<video style="max-width:100%;" controls="" poster="pcb.jpg"> - <source src="video.mp4" type="video/mp4" /> -</video> - -<h2 id="overview">Overview</h2> - -<p>The lock comprises three subsystems: the ATmega328P microcontroller, an R503 -fingerprint sensor, and an FS5106B high-torque servo. The sensor mounted on the -front surface of the door enables users to unlock it from the outside. The -servo is attached to the interior door knob. The MCU must be installed at the -back of the door to prevent unauthorized users from tampering with it.</p> - -<p>When no one is interacting with the lock, the MCU is in deep sleep. The sensor -and the servo each draw 13.8mA and 4.6mA of quiescent currents. To prevent this -idle current draw, the MCU employs MOSFETs to cut off power to them before -entering deep sleep. Doing so is crucial for conserving the battery.</p> - -<p>Without power, the sensor remains in a low-power state, drawing approximately -2.9μA through a separate power rail. When a finger comes into contact with the -sensor, the sensor triggers a pin change interrupt, waking up the MCU. The MCU -activates a MOSFET, which in turn activates the sensor. Over UART, the MCU -unlocks the sensor and issues commands to scan and match the fingerprint.</p> - -<p>If the fingerprint matches an enrolled fingerprint, the MCU activates the blue -LED on the sensor, turns on the MOSFET connected to the servo, and sends a PWM -signal to the servo to unlock the door. Otherwise, the MCU activates the red -LED on the sensor. Finally, the MCU deactivates the MOSFETS and goes back to -sleep.</p> - -<h2 id="embedded-software">Embedded software</h2> - -<p>The embedded software, written in C, includes a driver for the sensor, servo -control routines, and a battery monitoring system.</p> - -<p>In addition to controlling the sensor and the servo, the program strives to -maintain precise control over the microcontroller’s sleep modes, as well as -when the peripherals are activated and for how long they remain active. I -thoroughly enjoyed writing the embedded software. There’s something magical -about being able to alter the physical world around you by uttering a few lines -of C code.</p> - -<p>The source code of the project, which includes a driver for the R503 -fingerprint sensor module, is enclosed in the tarball linked at the end of the -page.</p> - -<h2 id="the-pcb">The PCB</h2> - -<p>For this project, I designed a custom PCB and had it fabricated by JLCPCB. Like -the software, the circuit is primarily concerned with optimizing power -consumption and extending battery life.</p> - -<table style="border: none; width: 100%"> - <tr style="border: none;"> - <td style="border: none; width: 49.9%; background-color: transparent; text-align: center;"> - <img src="breadboard.jpg" alt="PCB" style="width: 100%" /> - </td> - <td style="border: none; background-color: transparent; text-align: center;"> - <img src="pcb1.jpg" alt="Design" style="width: 100%" /> - </td> - </tr> - <tr style="border: none;"> - <td colspan="2" style="border: none; background-color: transparent; text-align: center;"> - <img src="footprint.png" alt="PCB footprint" style="width: 100%" /> - </td> - </tr> -</table> - -<p>Consequently, the principal components of the circuit are the 2N7000 and -NDP6020P field-effect transistors. They switch power electronically to the -servo and the fingerprint sensor, the two most power-hungry parts of the -circuit. The two MP1584EN buck converters play an axial role in efficiently -regulating power to the MCU and the sensor.</p> - -<p>The ATmega328P typically operates at 5V with a 16MHz crystal oscillator. To -further reduce power consumption, I modified the ATmega328P’s fuses to run at -3.3V with an 8MHz crystal oscillator.</p> - -<p>The bottom right area of the PCB isolates the power supply of the servo from -the rest of the circuit. This shields components such as the MCU from the -servo’s high current draw, which can exceed 1A. The IN4007 diode in slot U2 -serves as a flyback diode, protecting the MOSFET from reverse currents -generated by the servo.</p> - -<p>Lastly, the 56kΩ and 10kΩ resistors in slots R10 and R11 form a voltage divider -circuit. Its output is fed to the ADC of the MCU, which measures the supply -voltage by comparing it to the internal bandgap reference voltage.</p> - -<h2 id="epilogue">Epilogue</h2> - -<p>This project began nearly a year ago when I attempted to unlock our door -wirelessly by writing to the UART ports of two MCUs connected to inexpensive -433MHz RF transceivers. Although I failed, it led me down a rabbit hole of RF -communications, MOSFETs, PCB design, and low-power circuits.</p> - -<p>During the project, I reinvented the wheel many times. I implemented a -low-level network stack using only RF modules and an 8-bit microcontroller, -designed my first PCB, and developed drivers from scratch. The project was far -from a smooth sail. Bad electrical connections, soldering and desoldering, and -the heartache of purchasing the wrong parts were routine. It was a long but -rewarding journey from the messy breadboard to the shiny PCB.</p> - -<p>Files: <a href="source.tar.gz">source.tar.gz</a>, <a href="gerber.zip">gerber.zip</a></p> diff --git a/_log/_site/fpm-door-lock/breadboard.jpg b/_log/_site/fpm-door-lock/breadboard.jpg Binary files differdeleted file mode 100644 index 2bf47a9..0000000 --- a/_log/_site/fpm-door-lock/breadboard.jpg +++ /dev/null diff --git a/_log/_site/fpm-door-lock/footprint.png b/_log/_site/fpm-door-lock/footprint.png Binary files differdeleted file mode 100644 index 5511bf1..0000000 --- a/_log/_site/fpm-door-lock/footprint.png +++ /dev/null diff --git a/_log/_site/fpm-door-lock/gerber.zip b/_log/_site/fpm-door-lock/gerber.zip Binary files differdeleted file mode 100644 index 19a9d19..0000000 --- a/_log/_site/fpm-door-lock/gerber.zip +++ /dev/null diff --git a/_log/_site/fpm-door-lock/pcb.jpg b/_log/_site/fpm-door-lock/pcb.jpg Binary files differdeleted file mode 100644 index fbd800b..0000000 --- a/_log/_site/fpm-door-lock/pcb.jpg +++ /dev/null diff --git a/_log/_site/fpm-door-lock/pcb1.jpg b/_log/_site/fpm-door-lock/pcb1.jpg Binary files differdeleted file mode 100644 index 367187d..0000000 --- a/_log/_site/fpm-door-lock/pcb1.jpg +++ /dev/null diff --git a/_log/_site/fpm-door-lock/source.tar.gz b/_log/_site/fpm-door-lock/source.tar.gz Binary files differdeleted file mode 100644 index ef23422..0000000 --- a/_log/_site/fpm-door-lock/source.tar.gz +++ /dev/null diff --git a/_log/_site/fpm-door-lock/thumb_sm.jpg b/_log/_site/fpm-door-lock/thumb_sm.jpg Binary files differdeleted file mode 100644 index a8fa534..0000000 --- a/_log/_site/fpm-door-lock/thumb_sm.jpg +++ /dev/null diff --git a/_log/_site/fpm-door-lock/video.mp4 b/_log/_site/fpm-door-lock/video.mp4 Binary files differdeleted file mode 100644 index a907a9b..0000000 --- a/_log/_site/fpm-door-lock/video.mp4 +++ /dev/null diff --git a/_log/_site/matrix-digital-rain.html b/_log/_site/matrix-digital-rain.html deleted file mode 100644 index 85bac5d..0000000 --- a/_log/_site/matrix-digital-rain.html +++ /dev/null @@ -1,103 +0,0 @@ -<p>The Matrix digital rain implemented in raw C using ANSI escape sequences with -zero dependencies—not even ncurses.</p> - -<video style="max-width:100%;" controls="" poster="poster.png"> - <source src="matrix.mp4" type="video/mp4" /> -</video> - -<p>This project began over three years ago as a fork of Domsson’s unique rendition -of the Matrix rain: <a href="https://github.com/domsson/fakesteak" class="external" target="_blank" rel="noopener noreferrer">Fakesteak</a>. I -aimed to modify the algorithm to produce a rain that resembled the original -with high visual fidelity.</p> - -<h2 id="unicode-support">Unicode support</h2> - -<p>Unicode support in the 2022 version lacked flexibility. The charset used in the -rain had to be a single contiguous block defined by <code class="language-plaintext highlighter-rouge">UNICODE_MIN</code> and -<code class="language-plaintext highlighter-rouge">UNICODE_MAX</code> settings:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>#define UNICODE_MIN 0x0021 -#define UNICODE_MAX 0x007E - -static inline void insert_code(matrix *mat, - size_t row, size_t col) -{ - mat->code[index(mat, row, col)] = rand() - % (UNICODE_MAX - UNICODE_MIN) - + UNICODE_MIN; -} -</code></pre></div></div> - -<p>There was no way, for instance, to use both ASCII and Katakana at the same -time. The user had to pick one. In the new version, the user can use any number -of Unicode blocks using <code class="language-plaintext highlighter-rouge">glyphs</code> array. In fact, the default rain now includes -both ASCII and half-width Katakana characters:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>#define UNICODE(min, max) (((uint64_t)max << 32) | min) - -static uint64_t glyphs[] = { - UNICODE(0x0021, 0x007E), /* ASCII */ - UNICODE(0xFF65, 0xFF9F), /* Half-width Katakana */ -}; - -static uint8_t glyphlen = (sizeof glyphs) / (sizeof glyphs[0]); - -static inline void insert_code(matrix *mat, - size_t row, size_t col) -{ - uint64_t block; - uint32_t unicode_min, unicode_max; - - block = glyphs[(rand() % glyphlen)]; - unicode_min = (uint32_t)block; - unicode_max = (uint32_t)(block >> 32); - - mat->code[index(mat, row, col)] = rand() - % (unicode_max - unicode_min) - + unicode_min; -} -</code></pre></div></div> - -<p>Entries in the <code class="language-plaintext highlighter-rouge">glyphs</code> array are Unicode blocks bit-packed in an 8-byte -container: the four low bytes forms the first codepoint and the four high bytes -the last.</p> - -<h2 id="phosphor-decay">Phosphor decay</h2> - -<p>The dim afterglow of monochrome CRT displays is achieved by carefully scaling -the RGB channels individually and mixing them:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>#define DECAY_MPLIER 2 - -static inline void blend(matrix *mat, - size_t row, size_t col) -{ - unsigned char *color; - - color = mat->rgb[index(mat, row, col)].color; - color[R] = color[R] - (color[R] - RGB_BG_RED) / DECAY_MPLIER; - color[G] = color[G] - (color[G] - RGB_BG_GRN) / DECAY_MPLIER; - color[B] = color[B] - (color[B] - RGB_BG_BLU) / DECAY_MPLIER; -} -</code></pre></div></div> - -<p>The blending function emulates the phosphor decay by gradually transitioning -each raindrop’s color towards the background color. The multiplier is the -number of passes over the rain track needed before the afterglow disappears.</p> - -<p>Nonetheless, the rain resembles the original with high visual fidelity. It’s -highly customizable and gentle on the CPU. On my 14” ThinkPad T490, which has a -resolution of 1920x1080 and 4GHz CPU, it uses 2-3% of the CPU with occasional -jumps of up to about 8%. Not too bad for a weekend project. The program has -been tested with xterm and urxvt terminal emulators on OpenBSD and Arch Linux -systems. Someone has managed to get it moving on a Raspberry Pi as well.</p> - -<p>Lastly, to compile and run:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ cc -O3 main.c -o matrix -$ ./matrix -</code></pre></div></div> - -<p>“All I see is blonde, brunette, red head.”</p> - -<p>Files: <a href="source.tar.gz">source.tar.gz</a></p> diff --git a/_log/_site/matrix-digital-rain/katakana.png b/_log/_site/matrix-digital-rain/katakana.png Binary files differdeleted file mode 100644 index b9df873..0000000 --- a/_log/_site/matrix-digital-rain/katakana.png +++ /dev/null diff --git a/_log/_site/matrix-digital-rain/matrix.mp4 b/_log/_site/matrix-digital-rain/matrix.mp4 Binary files differdeleted file mode 100644 index 7edf5d6..0000000 --- a/_log/_site/matrix-digital-rain/matrix.mp4 +++ /dev/null diff --git a/_log/_site/matrix-digital-rain/poster.png b/_log/_site/matrix-digital-rain/poster.png Binary files differdeleted file mode 100644 index 1f68ca4..0000000 --- a/_log/_site/matrix-digital-rain/poster.png +++ /dev/null diff --git a/_log/_site/matrix-digital-rain/source.tar.gz b/_log/_site/matrix-digital-rain/source.tar.gz Binary files differdeleted file mode 100644 index 5a69236..0000000 --- a/_log/_site/matrix-digital-rain/source.tar.gz +++ /dev/null diff --git a/_log/_site/matrix-digital-rain/thumb_sm.png b/_log/_site/matrix-digital-rain/thumb_sm.png Binary files differdeleted file mode 100644 index 940965a..0000000 --- a/_log/_site/matrix-digital-rain/thumb_sm.png +++ /dev/null diff --git a/_log/_site/mosfet-switches.html b/_log/_site/mosfet-switches.html deleted file mode 100644 index c1a7b52..0000000 --- a/_log/_site/mosfet-switches.html +++ /dev/null @@ -1,110 +0,0 @@ -<p>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.</p> - -<h2 id="acknowledgments">Acknowledgments</h2> - -<p>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 <a href="https://electronics.stackexchange.com/users/292884/simon-fitch" class="external" target="_blank" rel="noopener noreferrer">Simon Fitch</a>.</p> - -<h2 id="preamble">Preamble</h2> - -<p>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).</p> - -<p>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> - -<h2 id="p-channel-high-side-switch">P-channel high-side switch</h2> - -<p>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> - -<p><img src="p_high_side.png" alt="P-channel high-side switching circuit" /></p> - -<p>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.</p> - -<h2 id="n-channel-high-side-switch">N-channel high-side switch</h2> - -<p>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:</p> - -<p><img src="n_high_side.png" alt="N-channel high-side switching circuit" /></p> - -<p>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.</p> - -<p>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.</p> - -<p>The D1 flyback diodes used in the two topologies safeguard the MOSFET from -voltage spikes caused by inductive loads such as servos.</p> - -<h2 id="a-bjt-alternative">A BJT alternative</h2> - -<p>A Bipolar Junction Transistor (BJT) is a simpler, cheaper, and more widely -available type of transistor that can be used as a switch.</p> - -<p><img src="bjt.png" alt="BJT architecture" /></p> - -<p>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. <a href="https://teachmetomake.wordpress.com/how-to-use-a-transistor-as-a-switch/" class="external" target="_blank" rel="noopener noreferrer">“How to choose a -transistor as a switch”</a> is an excellent guide on using BJTs as electronic -switches.</p> - -<h2 id="which-topology-to-choose">Which topology to choose?</h2> - -<p>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 V<sub>GS</sub> potentials -required to achieve specified R<sub>DS(on)</sub> values (i.e., to turn them on -fully).</p> - -<p>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.</p> - -<h2 id="further-reading">Further reading</h2> - -<ul> - <li><a href="https://www.embeddedrelated.com/showarticle/98.php" class="external" target="_blank" rel="noopener noreferrer">Different MOSFET -topologies</a></li> - <li><a href="https://www.embeddedrelated.com/showarticle/809.php" class="external" target="_blank" rel="noopener noreferrer">How to read -MOSFET datasheets</a></li> - <li><a src="https://teachmetomake.wordpress.com/how-to-use-a-transistor-as-a-switch/" class="external" target="_blank" rel="noopener noreferrer">How to use a -transistor as a switch</a></li> - <li><a src="https://forum.digikey.com/t/guide-to-selecting-and-controlling-a-mosfet-for-3-3-vdc-logic-applications/42606" class="external" target="_blank" rel="noopener noreferrer">Guide to -selecting and controlling a MOSFET for 3.3 VDC logic applications</a></li> - <li><a src="https://forum.digikey.com/t/driving-a-large-relay-from-a-3-3-vdc-microcontroller-using-an-npn-darlington-transistor/41751" class="external" target="_blank" rel="noopener noreferrer">Driving a large -relay from a 3.3 VDC microcontroller using an NPN Darlington transistor</a></li> -</ul> diff --git a/_log/_site/mosfet-switches/bjt.png b/_log/_site/mosfet-switches/bjt.png Binary files differdeleted file mode 100644 index 9858fa7..0000000 --- a/_log/_site/mosfet-switches/bjt.png +++ /dev/null diff --git a/_log/_site/mosfet-switches/n_high_side.png b/_log/_site/mosfet-switches/n_high_side.png Binary files differdeleted file mode 100644 index c851768..0000000 --- a/_log/_site/mosfet-switches/n_high_side.png +++ /dev/null diff --git a/_log/_site/mosfet-switches/p_high_side.png b/_log/_site/mosfet-switches/p_high_side.png Binary files differdeleted file mode 100644 index 9f5397a..0000000 --- a/_log/_site/mosfet-switches/p_high_side.png +++ /dev/null diff --git a/_log/_site/my-first-pcb.html b/_log/_site/my-first-pcb.html deleted file mode 100644 index d5e886b..0000000 --- a/_log/_site/my-first-pcb.html +++ /dev/null @@ -1,57 +0,0 @@ -<p>In 2023, I started tinkering with DIY electronics as a hobby. Until now, I’ve -been using development boards like the Arduino Uno and ESP-32-WROOM so that I -can focus on the software. Recently, I decided to step outside of my comfort -zone and design a PCB from scratch for a door lock I’m working on.</p> - -<p>The lock comprises two subsystems: a fingerprint sensor in front of the door -and a servo connected to the physical lock behind the door. The fingerprint -sensor authenticates the person and signals the servo behind the door to unlock -the door over an encrypted RF channel.</p> - -<table style="border: none; width: 100%"> - <tr style="border: none;"> - <td style="border: none; width: 49.5%; vertical-align: top; text-align: center;"> - <img src="front_design.jpeg" alt="Design (front)" style="width: 100%" /> - <p>Footprint (front)</p> - </td> - <td style="border: none; vertical-align: top; text-align: center;"> - <img src="front.jpeg" alt="PCB (front)" style="width: 100%" /> - <p>PCB (front)</p> - </td> - </tr> - <tr style="border: none;"> - <td style="border: none; width: 49.5%; vertical-align: top; text-align: center;"> - <img src="back_design.jpeg" alt="Design (back)" style="width: 100%" /> - <p>Footprint (back)</p> - </td> - <td style="border: none; vertical-align: top; text-align: center;"> - <img src="back.jpeg" alt="PCB (back)" style="width: 100%" /> - <p>PCB (back)</p> - </td> - </tr> -</table> - -<p>The PCBs have two layers. A copper region serves as the ground plane. The 0.3mm -wide 1oz/ft<sup>2</sup> copper traces can carry up to 500mA (the tracks -connecting the power source and the linear regulators have a width of 0.5mm). -Both subsystems were functional. I was able to control the servo reliably using -the fingerprint sensor.</p> - -<p>The designs aren’t without flaws, however. The main shortcoming of the circuits -is that they draw significant amounts of quiescent currents despite employing -sleep modes. The linear regulators were a poor choice as they dissipate too -much heat. The fingerprint sensor and the servo draw 13.8mA (3.3V) and 4.6mA -(5V) respectively, as long as they are connected to the power supply.</p> - -<p>Although the circuit didn’t draw more than 200mA without a load, the servo -under load could draw up to 600mA. I’m sailing too close to the wind with 0.3mm -copper traces. Instead, 0.4mm wide 2oz/ft<sup>2</sup> traces would have been -safer.</p> - -<p>I’m working on improving the design to reduce idle current consumption and -extend the battery life. Despite its deficiencies, this was my first PCB -design, and I’m glad that it worked as well as it did. Custom PCB design marks -an important milestone in my DIY electronics journey.</p> - -<p>Files: <a href="gerber_back.zip">gerber_back.zip</a>, <a href="gerber_front.zip">gerber_front.zip</a>, - <a href="source.tar.gz">source.tar.gz</a></p> diff --git a/_log/_site/my-first-pcb/back.jpeg b/_log/_site/my-first-pcb/back.jpeg Binary files differdeleted file mode 100644 index f458e69..0000000 --- a/_log/_site/my-first-pcb/back.jpeg +++ /dev/null diff --git a/_log/_site/my-first-pcb/back_design.jpeg b/_log/_site/my-first-pcb/back_design.jpeg Binary files differdeleted file mode 100644 index b6c0f5d..0000000 --- a/_log/_site/my-first-pcb/back_design.jpeg +++ /dev/null diff --git a/_log/_site/my-first-pcb/front.jpeg b/_log/_site/my-first-pcb/front.jpeg Binary files differdeleted file mode 100644 index 2b2931f..0000000 --- a/_log/_site/my-first-pcb/front.jpeg +++ /dev/null diff --git a/_log/_site/my-first-pcb/front_design.jpeg b/_log/_site/my-first-pcb/front_design.jpeg Binary files differdeleted file mode 100644 index f81f09c..0000000 --- a/_log/_site/my-first-pcb/front_design.jpeg +++ /dev/null diff --git a/_log/_site/my-first-pcb/gerber_back.zip b/_log/_site/my-first-pcb/gerber_back.zip Binary files differdeleted file mode 100644 index 26659ad..0000000 --- a/_log/_site/my-first-pcb/gerber_back.zip +++ /dev/null diff --git a/_log/_site/my-first-pcb/gerber_front.zip b/_log/_site/my-first-pcb/gerber_front.zip Binary files differdeleted file mode 100644 index 864334e..0000000 --- a/_log/_site/my-first-pcb/gerber_front.zip +++ /dev/null diff --git a/_log/_site/my-first-pcb/source.tar.gz b/_log/_site/my-first-pcb/source.tar.gz Binary files differdeleted file mode 100644 index c31aa22..0000000 --- a/_log/_site/my-first-pcb/source.tar.gz +++ /dev/null diff --git a/_log/_site/my-first-pcb/thumb_sm.jpeg b/_log/_site/my-first-pcb/thumb_sm.jpeg Binary files differdeleted file mode 100644 index c275b12..0000000 --- a/_log/_site/my-first-pcb/thumb_sm.jpeg +++ /dev/null diff --git a/_log/_site/neo4j-a-star-search.html b/_log/_site/neo4j-a-star-search.html deleted file mode 100644 index 9903abc..0000000 --- a/_log/_site/neo4j-a-star-search.html +++ /dev/null @@ -1,307 +0,0 @@ -<p>Back in 2018, we used <a href="https://neo4j.com/" class="external" target="_blank" rel="noopener noreferrer">Neo4J</a> 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. Graph theoretic -algorithms provide optimal solutions to such problems, and the set of route -points lends itself well to graph-based modelling.</p> - -<p>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 the weights. For various reasons, people are interested in -minimizing (or maximizing) the weight of a path through a set of vertices, such -as the shortest path between two ports to predict a vessel’s arrival time.</p> - -<p>Given 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 time complexity of this exhaustive search prevented our -database from scaling beyond 4,000 route points.</p> - -<p>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:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>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; - } - } -} -</code></pre></div></div> - -<p>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 <a href="https://github.com/neo4j-contrib/neo4j-graph-algorithms/releases/tag/3.4.0.0" class="external" target="_blank" rel="noopener noreferrer">v3.4.0</a> of the -Neo4J graph algorithms shipped with our A* search algorithm.</p> - diff --git a/_log/_site/robots.txt b/_log/_site/robots.txt deleted file mode 100644 index e087884..0000000 --- a/_log/_site/robots.txt +++ /dev/null @@ -1 +0,0 @@ -Sitemap: /sitemap.xml diff --git a/_log/_site/sitemap.xml b/_log/_site/sitemap.xml deleted file mode 100644 index 8c167bd..0000000 --- a/_log/_site/sitemap.xml +++ /dev/null @@ -1,36 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<urlset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd" xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"> -<url> -<loc>/arduino-due.html</loc> -</url> -<url> -<loc>/arduino-uno.html</loc> -</url> -<url> -<loc>/bumblebee.html</loc> -</url> -<url> -<loc>/e-reader.html</loc> -</url> -<url> -<loc>/etlas.html</loc> -</url> -<url> -<loc>/fpm-door-lock.html</loc> -</url> -<url> -<loc>/matrix-digital-rain.html</loc> -</url> -<url> -<loc>/mosfet-switches.html</loc> -</url> -<url> -<loc>/my-first-pcb.html</loc> -</url> -<url> -<loc>/neo4j-a-star-search.html</loc> -</url> -<url> -<loc>/suckless-software.html</loc> -</url> -</urlset> diff --git a/_log/_site/suckless-software.html b/_log/_site/suckless-software.html deleted file mode 100644 index d91ed16..0000000 --- a/_log/_site/suckless-software.html +++ /dev/null @@ -1,78 +0,0 @@ -<p>Since <a href="https://suckless.org/" class="external" target="_blank" rel="noopener noreferrer">suckless</a> 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.</p> - -<h2 id="initial-setup">Initial setup</h2> - -<p>When using a suckless program, I usually begin by cloning the project and -setting the remote push URL to my own git repository:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>git clone git://git.suckless.org/dwm -git reset --hard <tag> -git remote set-url --push origin git@git.asciimx.com:/repos/dwm -</code></pre></div></div> - -<p>This way, I can pull updates from the upstream project whenever I want, while -committing my changes to my git repository. The git reset command aligns my -branch head with a stable release before applying patches or installing the -software.</p> - -<p>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 -<code class="language-plaintext highlighter-rouge">make clean <target></code> command will generate it from the defaults and compile -the software. The <code class="language-plaintext highlighter-rouge"><target></code> is the name of the application (e.g., dwm) found -in the Makefile. I modify the resulting config.h file and run <code class="language-plaintext highlighter-rouge">make clean -install</code> to install the software before committing and pushing my changes to -the git repo.</p> - -<h2 id="dwm-and-slstatus">dwm and slstatus</h2> - -<p>Since dwm and slstatus are always running, <code class="language-plaintext highlighter-rouge">make install</code> will likely fail for -them. The operating system may prevent the installer from replacing running -executables with new ones. Hence, we must first stop the running instances of -these programs (in my case, using 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 <code class="language-plaintext highlighter-rouge">make install</code> to install the software and switch back to the -graphical session (Ctrl + Alt + F5).</p> - -<p>The key combinations for switching to the tty and back may differ across -systems. The ones listed above are for OpenBSD.</p> - -<h2 id="subsequent-upgrades">Subsequent upgrades</h2> - -<p>When suckless releases a new version, I run <code class="language-plaintext highlighter-rouge">git pull --rebase</code> 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.</p> - -<p>Commit log before upgrading:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>dt236 My patch. -3fkdf Version 6.5. -</code></pre></div></div> - -<p>Commit log after pulling:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>w467d My patch. -gh25g A commit. -g525g Another commit. -3fkdf Version 6.6. -vd425 Old commit. -q12vu Another old commit. -3fkdf Version 6.5. -</code></pre></div></div> - -<p>Commit log after the interactive rebase:</p> - -<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>h57jh My patch. -3fkdf Version 6.6. -vd425 Old commit. -q12vu Another old commit. -3fkdf Version 6.5. -</code></pre></div></div> - -<p>And finally, I commit and push all the changes to my git repository.</p> - diff --git a/_log/site-search.md b/_log/site-search.md index 6af9f63..d178d07 100644 --- a/_log/site-search.md +++ b/_log/site-search.md @@ -1,25 +1,49 @@ --- -title: Perl + FastCGI + SA search engine -date: 2026-01-02 +title: Search engine (Perl + FastCGI + SA) +date: 2026-01-03 layout: post --- -Number of articles growing. Need search. +Article count on the website is growing. Need a way to search. -Requirements: substring match, case-insensitive, fast, secure. No JavaScript. +Requirements: matches substrings, case-insensitive, fast, secure. No +JavaScript. -Architecture: OpenBSD httpd → slowcgi (FastCGI) → Perl script. +Architecture: browser → httpd → slowcgi → Perl CGI script. -Data structure: suffix array. Three files: corpus.bin (articles), sa.bin -(sorted byte offsets), file_map.dat (metadata). +httpd, slowcgi, Perl are in the OpenBSD base system. No dependencies. Access +governed by file system permissions--no secrets to manage. Secure by default. -Indexer crawls posts, extracts HTML with regex, lowercases, concatenates. Null -byte sentinel for document boundaries. Sort lexicographically:: +2025-12-30: Regex search. Wrote a 140-line Perl script that searches HTML files +using Regex. Script slurps 500 files (16 KB each) in 40 milliseconds. Fast +enough. Start to feel the O(N) pull at higher file counts. + +Regex and the site crawl introduce ReDoS and symlink attack vectors. Both can +be mitigated. Tempted to stop here. + +2026-01-03: Suffix array (SA) based index lookup. + +Inefficiency of scanning every file on each request troubles me. Regex search +depends almost entirely on hardware for speed. + +Built SA index comprising three files: corpus.bin (articles), sa.bin (sorted +byte offsets), file_map.dat (metadata). Index created with the site: + +``` +$ JEKYLL_ENV=production bundle exec jekyll build +$ cd cgi-bin/ +$ perl indexer.pl +``` + +Indexer extracts HTML, lowercases, encodes text as UTF-8 binary sequences, and +saves to corpus.bin. Null byte sentinel marks the document boundaries. Suffix +array stores offsets of all suffixes as 32-bit unsigned integers, sorted by the +lexicographical order: ``` -# Use a block that forces byte-level comparison +my @sa = 0 .. (length($corpus) - 1); { - use bytes; + use bytes; # Force compare 8-bit Unicode value comparisons @sa = sort { # First 64 bytes check (fast path) (substr($corpus, $a, 64) cmp substr($corpus, $b, 64)) || @@ -27,31 +51,73 @@ byte sentinel for document boundaries. Sort lexicographically:: (substr($corpus, $a) cmp substr($corpus, $b)) } @sa; } + +CORPUS: a s c i \0 i m x +OFFSET: 0 1 2 3 4 5 6 7 + +SORTED SUFFIXES: + +[4] \0imx +[0] asci\0imx +[2] ci\0imx +[3] i\0imx <-- "i" from "asci" +[5] imx <-- "i" from "imx" +[6] mx +[1] sci\0imx +[7] x +``` + +Algorithmic complexity: O(L⋅N log N). Fast path caps L at 64 bytes (length of a +cache line), reducing complexity to O(N log N). + +Search: Textbook range query with two binary searches. Random access to offsets +and the text is possible via the fixed-width offsets: + +``` +seek($fh_sa, $mid * 4, 0); +read($fh_sa, my $bin_off, 4); +my $off = unpack("L", $bin_off); +seek($fh_cp, $off, 0); +read($fh_cp, my $text, $query_len); ``` -Slow path: O(L⋅N log N). Fast path caps L at 64 bytes → O(N log N). 64-byte -length targets cache lines. +Small seek/reads are fast on modern SSDs. Keeps memory usage low, and was easy +to implement. Note to self: mmap. -Search: binary search for range query. Cap at 20 results--define limits or be -surprised by them. +Benchmarks on T490 (i7-10510U, OpenBSD 7.8, article size: 16 KB). -File IO and memory: many seek/read small chunks beat one large allocation (see -benchmarks for find_one_file.cgi). +500 files: + - Index size: 204.94 KB + - Indexing time: 0.1475 s + - Peak RAM (SA): 8828 KB + - Peak RAM (Regex): 9136 KB + - Search (SA): 0.0012 s + - Search (Regex): 0.0407 s -Benchmarks on T490 (i7-10510U, OpenBSD 7.8, 16KB articles): +1,000 files: + - Index size: 410.51 KB + - Indexing time: 0.3101 s + - Peak RAM (SA): 8980 KB + - Peak RAM (Regex): 9460 KB + - Search (SA): 0.0019 s + - Search (Regex): 0.0795 s -1,000 files: 0.31s indexing, 410 KB total index. -10,000 files: 10.97s indexing, 4.16 MB total index. +10,000 files: + - Index size: 4163.44 KB + - Indexing time: 10.9661 s + - Peak RAM (SA): 12504 KB + - Peak RAM (Regex): 12804 KB + - Search (SA): 0.0161 s + - Search (Regex): 0.9120 s -Search 'arduino' (0 matches): -1,000 files: 0.002s (SA) vs 0.080s (naive regex). -10,000 files: 0.016s (SA) vs 0.912s (naive regex). +Security: Much of it comes from its architectural simplicity. No dependencies +to manage, no secrets to hide, no assets for lateral movement. Runs in chroot. -Security. Semaphore (lock files) limits parallel queries. Escape HTML (XSS). -Sanitize input--strip non-printables, limit length, and quote metacharacters -(ReDOS). No exec/system (command injection). Chroot. +Resource exhaustion and XSS attacks are inherent. The former is mitigated by +limiting concurrent searches via lock-file semaphores and capping query length +(64B) and result sets (20). All output is HTML-escaped to prevent XSS. -Verdict: Fast SA lookup. Primary attack vectors mitigated. No dependencies. +Verdict: Fast SA lookup; Works on every conceivable web browser. Commit: [6da102d](https://git.asciimx.com/www/commit/?h=term&id=6da102d6e0494a3eac3f05fa3b2cdcc25ba2754e) |
