.thumb
.syntax unified

.include "gpio_constants.s"     // Register-adresser og konstanter for GPIO

.text
	.global Start

LED_PORT_BASE = GPIO_BASE + (LED_PORT * PORT_SIZE)
LED_SET_ADDR = LED_PORT_BASE  + GPIO_PORT_DOUTSET
LED_CLEAR_ADDR = LED_PORT_BASE + GPIO_PORT_DOUTCLR
BUTTON_READ_ADDR = GPIO_BASE + (BUTTON_PORT * PORT_SIZE) + GPIO_PORT_DIN
	
Start:
  LDR R0, =LED_SET_ADDR
  LDR R1, =LED_CLEAR_ADDR
  LDR R2, =BUTTON_READ_ADDR

Loop:
  LDR R3, [R2]                 // Read value of BUTTON_READ_ADDR
  AND R3, R3, 1 << BUTTON_PIN  // Mask out the bit of interest
  LSR R3, BUTTON_PIN - LED_PIN // Shift the bit to the LED_PIN position
  STR R3, [R1]                 // Store the value into LED_SET_ADDR
  EOR R3, R3, 1 << LED_PIN     // Flip the bit
  STR R3, [R0]                 // Store the opposite bit into LED_CLEAR_ADDR
  B Loop                       // Repeat
  NOP