#include "stm32f10x.h"                  // Device header

void led_on(void){
	// |=，&=，都要先读，修改，写回去，如果在中断里刚好操作同一GPIO就会出现竞争和电平紊乱，有读改写风险，推荐用BSRR
	//GPIOA->ODR |= (1ul << 1);
	GPIOA->BSRR = (1ul << 5); 
}

void led_off(void){
	//GPIOA->ODR &= ~(1ul << 1);
	GPIOA->BSRR = (1ul << 21); 
}

int main(void){
	RCC->APB2ENR |= (1ul << 2);
	//PA5推挽输出
	GPIOA->CRL &= ~(0x0F << (4 * 5));
	GPIOA->CRL |= (0x03 << (4 * 5));
	
	//PA6上拉输入
	GPIOA->CRL &= ~(0x0F << (4 * 6));
	GPIOA->CRL |= (0x08 << (4 * 6));
	
	while(1){
		//读到低电平——按下
		if(!(GPIOA->IDR & (1ul << 6))){
			led_on();
		}
		else{
			led_off();
		}
	}
}

流程：

1、开启RCC时钟

2、GPIO配置
 

注意移位操作就好，慢慢熟练。