#define GPIO_BASE 0x6000d000

void _start() {
  *(volatile unsigned int *)(0x60006010) |= (1 << 8);

  *(volatile unsigned int *)(GPIO_BASE + 0x500 + 0x14) = 0xFF; // Port U OE
  *(volatile unsigned int *)(GPIO_BASE + 0x600 + 0x14) = 0xFF; // Port V OE
  *(volatile unsigned int *)(GPIO_BASE + 0x500 + 0x10) = 0xFF; // Port U CNF
  *(volatile unsigned int *)(GPIO_BASE + 0x600 + 0x10) = 0xFF; // Port V CNF

  while (1) {
    *(volatile unsigned int *)(GPIO_BASE + 0x500 + 0x18) ^= 0xFF;
    *(volatile unsigned int *)(GPIO_BASE + 0x600 + 0x18) ^= 0xFF;

    for (volatile int i = 0; i < 200000; i++)
      ; // Visible delay
  }
}