---
title: Bare-metal ATSAM3X8E (Arduino Due)
date: 2024-09-16
layout: post
---

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

<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>

ATSAM3X8E boots into 0x00000, which is mapped to ROM. ROM contains the SAM-BA
bootloader.

Remap start address to flash0 (flash driver section, OpenOCD manual AT91SAM3):

```
$ openocd -f openocd-due.cfg
$ telnet localhost 4444
  > halt
  > at91sam3 gpnvm show
  > at91sam3 gpnvm set 1
  > at91sam3 gpnvm show
```

Place the vector table at the start of flash0 and initialize the stack pointer
to the top of the RAM:

```
MEMORY
{
    rom (rx)  : ORIGIN = 0x00080000, LENGTH = 512K
    ram (rwx) : ORIGIN = 0x20000000, LENGTH = 96K
}

SECTIONS
{
    .text :
    {
        KEEP(*(.vtor))  /* Vector table defined in main.c */
        *(.text*)
        *(.rodata*)
    } > rom

    /* Data, bss sections */
}

_sp = ORIGIN(ram) + LENGTH(ram); /* Descending stack */
```

Build and upload the program:

```
$ 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: <a
href="https://git.asciimx.com/bare-metal-arduino-due/commit/?id=318496925ca76668dd9d63c3d060376f489276f8"
class="external" target="_blank" rel="noopener noreferrer">3184969</a>.