Assembling Cortex-M assembly language by Arm GNU Toolchain

Build step

arm-none-eabi-as -g test.s -o test.o

arm-none-eabi-ld test.o -o test.elf

arm-none-eabi-objcopy -O binary test.elf test.bin

.syntax unified
.cpu cortex-m0
.thumb

.long 0x20000400        @ Main Stack Pointer    4-byte
.long 0x00000001        @ Reset vector          4-byte
.global _start
b _start                @ Jump to _start        2-byte

.org 0x0A
_start:
ldr r0, =0x0000dfff     @ PB13=0
ldr r1, =0x50004048     @ GPIOB_DOUT
str r0, [r1]            @ Store the value to GPIOB_DOUT
b .                     @ Endless loop

References

• ARM-ASM-Tutorial – Mikrocontroller.net
• How to boot a Cortex-M3 or Cortex-M4 processor with uninitialized memory at address zero
• Cortex-M0 Devices Generic User Guide Version 1.0