BCM2835 >> Assembly

Button

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參考資料：
1. example
2. firmware
3. datasheet
4. rpi_software

按鍵連接到GPIO-19


暫存器


Alternate Function


GPIO SET


GPIO CLR


main.s

  .global _start
  
  .equiv GPFSEL0,   0x20200000
  .equiv GPFSEL1,   0x20200004
  .equiv GPSET0,    0x2020001c
  .equiv GPCLR0,    0x20200028
  .equiv GPLEV0,    0x20200034
  .equiv GPPUD,     0x20200094
  .equiv GPPUDCLK0, 0x20200098
 
  .arm
  .text
_start:
  b reset
  b .
  b .
  b .
  b .
  b .
  b .
  b .
      
reset:
  ldr r0, =GPFSEL0
  ldr r1, =(1 << 15)
  str r1, [r0]
 
  ldr r0, =GPFSEL1
  ldr r1, =0x00000000
  str r1, [r0]
 
  ldr r0, =GPPUD
  ldr r1, =0x02
  str r1, [r0]
 
  ldr r0, =GPPUDCLK0
  ldr r1, =(1 << 19)
  str r1, [r0]
 
0:
  ldr r0, =GPLEV0
  ldr r1, [r0]
  and r1, #(1 << 19)
  cmp r1, #0
  ldrne r0, =GPCLR0
  ldreq r0, =GPSET0
  ldr r1, =(1 << 5)
  str r1, [r0]
  b 0b
  .end

完成

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