Не могу разобраться с кодом

GPIOA->CRL &= ~_CRL_MODE3;
GPIOA->CRL &= ~GPIO_CRL_CNF3;
GPIOA->CRL |=  GPIO_CRL_CNF3_0;

void delay(uint32_t del)
{
for(volatile uint32_t i = 0; i<del; i++); } void send_presence() {    GPIOA->ODR = GPIO_Pin_3;
delay(100);
GPIOA->ODR = 0;
delay(3500); //420us
GPIOA->ODR = GPIO_Pin_3;
}
 
void one_wire_write_bit(uint8_t bit)
{
GPIOA->ODR = 0;
delay(bit ? 150 : 500);
GPIOA->ODR = GPIO_Pin_3;
delay(bit ? 650 : 200);
}
 
uint8_t one_wire_read_bit()
{
uint8_t bit = 0;
GPIOA->ODR = 0;
delay(80);
GPIOA->ODR = _Pin_3;
delay(50);
GPIOA->CRL &= ~GPIO_CRL_MODE3;
GPIOA->CRL &= ~GPIO_CRL_CNF3;
GPIOA->CRL |=  GPIO_CRL_CNF3_0;
bit = (GPIOA->IDR&GPIO_Pin_3?1:0);
GPIOA->CRL |=  GPIO_CRL_MODE3;
GPIOA->CRL |=  GPIO_CRL_CNF3_0;
delay(600);
return bit;
}
 
void one_wire_write_byte(uint8_t data)
{
for(uint8_t i = 0; i<8; i++)       one_wire_write_bit(data>>i & 1);
}
 
int main()
{
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
 
GPIO_InitTypeDef  GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_3;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_OD;
GPIO_Init(GPIOA, &GPIO_InitStructure);
 
send_presence();
delay(5500);
one_wire_write_byte(0xCC);
one_wire_write_byte(0x4E);
one_wire_write_byte(0x4B);
one_wire_write_byte(0x46);
one_wire_write_byte(0x5F);
 
send_presence();
delay(5500);
one_wire_write_byte(0xCC);
one_wire_write_byte(0x44);
delay(6000000);
 
send_presence();
delay(5500);
one_wire_write_byte(0xCC);
one_wire_write_byte(0xBE);
delay(4000);
uint16_t data = 0;
for(uint8_t i = 0; i<16; i++) data += (uint16_t)one_wire_read_bit()<<i;
ftoot temp = data/16.0;
}

   GPIOA->ODR = 0;
delay(80);
GPIOA->ODR = _Pin_3;