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.set irq_handler, 0x18017920
.set irq_vector, 0x00000038

.arm
.text
_start:
.global _start
  @ store registers
  stmfd  sp!, {r4-r12,lr}
  bl    main

  @ restore irq vector
  ldr    r0, =irq_handler
  ldr    r1, =irq_vector
  str    r0, [r1]

  @ clear instruction cache
  mov     r0, #0
  mcr     p15, 0, r0, c7, c5
  nop
  nop
  nop
  nop

  @ restore registers
  ldmfd  sp!, {r4-r12,pc}
  b     done

done:
  @ branch to original exception handler
  ldr    pc, =irq_handler