改成用寄存器操作实现四个灯的跑马灯

好的，下面是用寄存器操作实现四个灯的跑马灯的代码：

#include "stm32f10x.h"

int main(void) {
    // 使能 GPIOB 时钟
    RCC->APB2ENR |= RCC_APB2ENR_IOPBEN;

    // 配置 PB0、PB1、PB2、PB12 为推挽输出模式，最大输出速率为 50MHz
    GPIOB->CRL &= ~(GPIO_CRL_MODE0 | GPIO_CRL_MODE1 | GPIO_CRL_MODE2);
    GPIOB->CRL |= (GPIO_CRL_MODE0_0 | GPIO_CRL_MODE1_0 | GPIO_CRL_MODE2_0);
    GPIOB->CRH &= ~(GPIO_CRH_MODE12);
    GPIOB->CRH |= GPIO_CRH_MODE12_0;

    while (1) {
        // 依次点亮 PB0、PB1、PB2、PB12
        GPIOB->BSRR = GPIO_BSRR_BS0;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR0;

        GPIOB->BSRR = GPIO_BSRR_BS1;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR1;

        GPIOB->BSRR = GPIO_BSRR_BS2;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR2;

        GPIOB->BSRR = GPIO_BSRR_BS12;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR12;

        // 依次点亮 PB12、PB2、PB1、PB0
        GPIOB->BSRR = GPIO_BSRR_BS12;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR12;

        GPIOB->BSRR = GPIO_BSRR_BS2;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR2;

        GPIOB->BSRR = GPIO_BSRR_BS1;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR1;

        GPIOB->BSRR = GPIO_BSRR_BS0;
        for (int i = 0; i < 1000000; i++);
        GPIOB->BSRR = GPIO_BSRR_BR0;
    }
}

这个代码可以让 PB0、PB1、PB2、PB12 这四个引脚的 LED 做跑马灯效果，每个灯亮 1 秒钟。