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diff --git a/_log/arduino-due.md b/_log/arduino-due.md index a0bfe4a..e24666c 100644 --- a/_log/arduino-due.md +++ b/_log/arduino-due.md @@ -1,17 +1,24 @@ --- -title: Bare-metal ATSAM3X8E +title: ATSAM3X8E bare-metal notes date: 2024-09-16 layout: post --- -Notes on programming bare-metal ATSAM3X8E chips (Arduino Due) using Serial Wire -Debug (SwD) protocol. +Bypassing ATSAM3X8E (Due) bootloader via Serial Wire Debug (SWD). -## Toolchain +Toolchain: ST-LINK/V2 programmer, OpenOCD, ARM GNU Compiler Toolchain. -ST-LINK/V2 programmer, OpenOCD, ARM GNU Compiler Toolchain. +ARM chips boot into 0x00000. GPNVM bits map one of ROM, flash0, flash1 to +0x00000: -## Electrical connections + - GPNVM1=0 → ROM (default). + - GPNVM1=1 and GPNVM2=0 → flash0. + - GPNVM1=1 and GPNVM2=1 → flash1. + +By default, control jumps to Atmel's SAM-BA bootloader in ROM. To bypass, set +GPNVM1=1 and place vector table at 0x80000 (flash0). + +Connect ST-LINK/v2 to Arduino Due's DEBUG port: <table style="border: none; width: 100%;"> <tr style="border: none;"> @@ -26,22 +33,7 @@ ST-LINK/V2 programmer, OpenOCD, ARM GNU Compiler Toolchain. </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. - -## Upload procedure - -Build. Magic is in the script.ld linker script. - -``` -$ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \ - -nostartfiles \ - -nostdlib \ - -o a.elf main.c -``` - - -Upload using OpenOCD: +Remap memory: ``` $ openocd -f openocd-due.cfg @@ -50,35 +42,19 @@ $ telnet localhost 4444 > at91sam3 gpnvm show > at91sam3 gpnvm set 1 > at91sam3 gpnvm show -$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit" ``` -First command starts OpenOCD. Telnet session halts chip, checks GPNVM bit. If -unset (returns 0), set to 1 and verify. Final command uploads program. See -OpenOCD manual AT91SAM3 flash driver section for full command list. +Full command list is in OpenOCD manual AT91SAM3 (flash driver section). -## GPNVM bits +Compile and upload program: -ARM chips boot into address 0x00000. ATSAM3X8E has ROM and dual-banked flash -(flash0/flash1) at different addresses. GPNVM bits control which maps to -0x00000. - -GPNVM1 cleared (default): boots from ROM (Atmel SAM-BA bootloader). GPNVM1=1, -GPNVM2=0: flash0 (0x80000) maps to 0x00000. Both cleared: flash1 maps to -0x00000. - -Program goes in flash0, so set GPNVM1=1 to boot our code instead of bootloader. - -## Linker script notes - -Vector table must be at first flash address--required for ARM chips unless -relocated using VTOR register. - -First vector table entry: stack pointer. Initialize to highest memory location -(ATSAM3X8E has descending stack). - -Second entry: reset vector. Place initialization code here (zero memory, set -registers) before jumping to main(). +``` +$ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \ + -nostartfiles \ + -nostdlib \ + -o a.elf main.c +$ openocd -f openocd-due.cfg -c "program a.elf verify reset exit" +``` Commit: [3184969](https://git.asciimx.com/bare-metal-arduino-due/commit/?id=318496925ca76668dd9d63c3d060376f489276f8) |