实验1

1.在键盘输入一个字符，串口工具进行显示

2.例如：在在键盘输入一个字符'a',串口工具进行显示'b'

实验2

1.在键盘输入一个字符串，串口工具进行显示

2.例如：在在键盘输入一个字符串“huyue”,串口工具进行显示“huyue”

include/uart4.h

#ifndef __UART4_H__
#define __UART4_H__

#include "stm32mp1xx_rcc.h"
#include "stm32mp1xx_gpio.h"
#include "stm32mp1xx_uart.h"

//初始化相关操作
void hal_uart4_init();

//发送一个字符
void hal_put_char(const char str);

//接收一个字符
char hal_get_char();

//发送一个字符串
void hal_put_string(const char *string);

//接收一个字符串
char *hal_get_string();

#endif

src/uart4.c

#include "uart4.h"

//初始化相关操作
void hal_uart4_init()
{
	/*-----RCC初始化-----*/
	//使能GPIOB/G
	RCC->MP_AHB4ENSETR |= (0X1 << 1);
	RCC->MP_AHB4ENSETR |= (0X1 << 6);

	//使能UART4
	RCC->MP_APB1ENSETR |= (0x1 << 16);


	/*-----GPIO初始化-----*/
	//设置引脚为复用功能模式
	GPIOB->MODER &= (~(0x3 << 4));
	GPIOB->MODER |= (0x1 << 5);
	GPIOG->MODER &= (~(0x3 << 22));
	GPIOG->MODER |= (0x1 << 23);

	//设置PB2引脚为UART4_RX模式
	GPIOB->AFRL &= (~(0xf << 8));
	GPIOB->AFRL |= (0x1 << 11);

	//设置PG11引脚为UART4_TX模式
	GPIOG->AFRH &= (~(0xf << 12));
	GPIOG->AFRH |= (0x3 << 13);


	/*-----UART初始化-----*/
	//8位数据位
	USART4->CR1 &= (~(0x1 << 28));
	USART4->CR1 &= (~(0x1 << 12));

	//16倍采样率
	USART4->CR1 &= (~(0x1 << 15));

	//无奇偶校验
	USART4->CR1 &= (~(0x1 << 10));

	//1位停止位
	USART4->CR2 &= (~(0x3 << 12));

	//波特率
	USART4->BRR &= (~(0xffff));
	USART4->BRR |= (0x22b);

	//不分频
	USART4->PRESC &= (~(0xf));

	//发送器使能
	USART4->CR1 |= (0x1 << 3);

	//接收器使能
	USART4->CR1 |= (0x1 << 2);

	//串口使能
	USART4->CR1 |= (0x1);

}

//发送一个字符
void hal_put_char(const char str)
{
	//判断发送数据寄存器是否为空
	while(!(USART4->ISR & (0x1 << 7)));

	//将发送的内容赋值给寄存器
	USART4->TDR = str;

	//判断发送是否完成
	while(!(USART4->ISR & (0x1 << 6)));
}


//接收一个字符
char hal_get_char()
{
	//判断是否接收到数据
	while(!(USART4->ISR & (0x1 << 5)));

	//将数据从寄存器中读出来
	char c = USART4->RDR;
	hal_put_char(c);
	hal_put_char('\n');
	hal_put_char('\r');
	return c;
}


//发送一个字符串
void hal_put_string(const char *string)
{
	int i = 0;
	while(*(string+i) != 0)
	{
		hal_put_char(*(string+i));
		i++;
	}
	hal_put_char('\n');
	hal_get_char('\r');
}


//接收一个字符串
char *hal_get_string()
{
	static char str[512];
	int i=0;
	while(1)
	{
		str[i] = hal_get_char();
		hal_put_char(str[i]);
		if(str[i] == '\r')
		{
			break;
		}
		i++;
	}
	str[i+1] = 0;
	hal_put_char('\n');
	hal_put_char('\r');
	return str;
}

main.c

#include "uart4.h"

extern void printf(const char *fmt, ...);
void delay_ms(int ms)
{
	int i,j;
	for(i = 0; i < ms;i++)
		for (j = 0; j < 1800; j++);
}

int main()
{
	hal_uart4_init();
	char c;
	
	while(1)
	{
		c = hal_get_char();
		hal_put_char(++c);
		hal_put_char('\n');
		hal_put_char('\r');
	}
	/*
	char *p;
	while(1)
	{
		p = hal_get_string();
		hal_put_string(p);
	}
	*/
	return 0;
}

运行结果