startup.s

  .syntax unified

  .text

  .global memset_reg
  .type memset_reg, STT_FUNC
memset_reg:
  // call with the following (note that the arguments are not validated prior to use):
  // r0 - address of first word to write (inclusive)
  // r1 - address of first word following the address in r0 to NOT write (exclusive)
  // r2 - word value to be written
  // both addresses in r0 and r1 needs to be divisible by 4!
  .L_loop_begin:
    str r2, [r0], 4 // store the word in r2 to the address in r0, post-indexed
    cmp r0, r1
  bne .L_loop_begin
  bx lr

  .global reset_handler
  .type reset_handler, STT_FUNC
reset_handler:
  ldr r0, =_ram_start // r0 - point to beginning of SRAM
  ldr r1, =_ram_end   // r1 - point to byte after the end of SRAM
  ldr r2, =0          // r2 - the byte-sized value to be written
  bl memset_reg

  // copy .data section from flash to SRAM
  ldr r0, =_data          // dst addr
  ldr r1, =_data_loadaddr // src addr
  ldr r2, =_data_size     // length in bytes
  bl memcpy

  // enter the application code
  bl main

  // loop forever if the application code returns
  b .

  .end