ATSAM3X8E bare-metal programming

Notes on programming ATSAM3X8E chips (Arduino Due) without bootloader. Tested -on OpenBSD.

Notes on programming bare-metal ATSAM3X8E chips (Arduino Due) using Serial Wire +Debug (SwD) protocol.

Toolchain

Need to bypass embedded bootloader—requires hardware programmer that speaks -Serial Wire Debug (SWD). ST-LINK/V2 works as SWD-USB adapter.

- -

OpenOCD translates commands to binary sequences the chip understands. Runs -telnet server on startup for issuing commands.

- -

ARM GNU Compiler Toolchain for compiling C programs. Both OpenOCD and ARM -toolchain available on OpenBSD.

ST-LINK/V2 programmer, OpenOCD, ARM GNU Compiler Toolchain.

Electrical connections

Arduino Due exposes ATSAM3X8E’s SWD interface via DEBUG port. ST-LINK/V2 -connects there.

@@ -86,8 +70,7 @@ ST-LINK/v2 programmer connects to that to communicate with the chip.

Upload procedure

Sample LED blink program with OpenOCD config and linker scripts in tarball -below.

Build. Magic is in the script.ld linker script.

$ arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -T script.ld \
     -nostartfiles \
@@ -95,7 +78,7 @@ below.
     -o a.elf main.c

Upload:

Upload using OpenOCD:

$ openocd -f openocd-due.cfg
 $ telnet localhost 4444
@@ -124,8 +107,8 @@ GPNVM2=0: flash0 (0x80000) maps to 0x00000. Both cleared: flash1 maps to
 
 Linker script notes
 
-Vector table must be at first flash address–mandatory for ARM chips unless
-using VTOR register for relocation.
+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).
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