diff options
Diffstat (limited to '_archive/arduino-due.md')
| -rw-r--r-- | _archive/arduino-due.md | 122 |
1 files changed, 0 insertions, 122 deletions
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 <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. - -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. - -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. - -## 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. - -<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> - -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) |