ARM day5

串口获取字符，控制LED灯的亮灭

#include "uart4.h"


void uart4_init()
{
    //使能GPIOB GPIOG UART4外设时钟
    RCC->MP_AHB4ENSETR |= (0x1<<1);//GPIOB
    RCC->MP_AHB4ENSETR |= (0x1<<6);//GPIOG
    RCC->MP_APB1ENSETR |= (0X1<<16);//UART4
    //设置PB2和PG11管脚复用
    GPIOB->MODER &= (~(0x3<<4));
    GPIOB->MODER |=(0x2<<4); 
    GPIOB->AFRL &= (~(0XF<<8));
    GPIOB->AFRL |= (0x8<<8);
    GPIOG->MODER &= (~(0x3<<22));
    GPIOG->MODER |=(0x2<<22); 
    GPIOG->AFRH &= (~(0XF<<12));
    GPIOG->AFRH |= (0x6<<12);
    //设置串口不使能 UE=0
    USART4->CR1 &= (~(0X1));
    //设置8位数据位
    USART4->CR1 &= (~(0x1<<12));
    USART4->CR1 &= (~(0x1<<28));
    //设置没有奇偶校验位
    USART4->CR1 &= (~(0x1<<10));
    //设置1位停止位
    USART4->CR2 &= (~(0x3<<12));
    //设置16倍过采样
    USART4->CR1 &= (~(0x1<<15));
    //设置时钟不分频
    USART4->PRESC &= (~(0xF));
    //设置波特率为115200
    USART4->BRR=0X22B;
    //使能发送器
    USART4->CR1 |= (0x1<<3);
    //使能接收器
     USART4->CR1 |= (0x1<<2);
    //使能uart4
     USART4->CR1 |= (0x1<<0);
    
}

//发送一个字符
void putchar(char a)
{
    //先判断发送数据寄存器是否为空
     //不为空阻塞等待
    while(!(USART4->ISR&(0x1<<7)));
    //为空向发送数据寄存器写入a的数据
   USART4->TDR=a;
    //写入完成需要判断发送是否完成，不完成阻塞等待，完成了则函数结束
    while(!(USART4->ISR&(0x1<<6)));
}

//接收一个字符
char getchar()
{
    char a;
    while(!(USART4->ISR&(0x1<<5)));
    a=USART4->RDR;
    return a;
}

//发送字符串
void puts(char *s)
{
    while(*s)
    {
        putchar(*s);
        s++;
    }
    putchar('\n');
    putchar('\r');

}

//接收字符串函数
void gets(char *s)
{
    while(1)
    {
        *s=getchar();
        putchar(*s);
        if((*s)=='\r')
            break;
        s++;
    }
    *s='\0';
    putchar('\n');
}