include/uart4.h 

#ifndef __UART4_H__
#define __UART4_H__

#include "stm32mp1xx_gpio.h"
#include "stm32mp1xx_rcc.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);

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

//接收一个字符
char hal_get_char();

//接收一个字符串
char* hal_get_string();

#endif

 src/yart4.c 

#include "uart4.h"
//PB2--->UART4_RX
//PG11--->UART4_TX

//初始化相关操作
void hal_uart4_init()
{
	//~~~~~~~~~~~~~RCC章节初始化~~~~~~~~~~~~~~~~~~~~~~~~//
	//使能AHB4初始化GPIOB GPIOG[1] [6] =1
	RCC->MP_AHB4ENSETR |= (0x21 << 1);   
	//使能APB1初始化[16]=1
	RCC->MP_APB1ENSETR |= (0x1 << 16); 

	//~~~~~~~~~~~~~GPIO章节初始化~~~~~~~~~~~~~~~~~~~~~~~//
	//GPIOB寄存器初始化 [5:4]=10
	GPIOB->MODER |= (0x1 << 5);         
	GPIOB->MODER &= (~(0x1 << 4));
	//GPIOB_AFRL设置引脚的复用功能模式[11:8]=1000
	GPIOB->AFRL |= (0x1 << 11);         
	GPIOB->AFRL &= (~(0x7 << 8));
	//GPIOG寄存器初始化 [23:22]=10
	GPIOG->MODER |= (0x1 << 23);       
	GPIOG->MODER &= (~(0x1 << 22));
	//GPIOG_AFRH设置引脚的复用功能模式[15:12]=0110
	GPIOG->AFRH |= (0xF << 15);         
	GPIOG->AFRH &= (~(0x9 << 15));   

	//~~~~~~~~~~~~~UART章节初始化~~~~~~~~~~~~~~~~~~~~~~//
	//0.设置串口UE=0 [0]=0
	USART4->CR1 &= (~(0x1));
	//1.设置1位的起始位，8位数据位 [28]=0 [12]=0 
	USART4->CR1 &= (~(0x1 << 12));
	USART4->CR1 &= (~(0x1 << 28));
	//2.没有校验位 CR1[10]=0
	USART4->CR1 &= (~(0x1 << 10));
	//3.设置1位停止位 CR2[13:12] =00
	USART4->CR2 &= (~(0x3 << 13));
	//4.设置16倍采样率 CR1[15]=0
	USART4->CR1 &= (~(0x1 << 15));
	//5.设置串口不分频 0000
	USART4->PRESC &= (~(0xF));
	//6.设置串口波特率为0x22b 时钟源/波特率  64000000/115200
	USART4->BRR = 0x22b;
	//7.设置串口发送器使能
	USART4->CR1 |= (0x1 << 3);
	//8.设置串口接收器使能
	USART4->CR1 |= (0x1 << 2);
	//9.设置串口使能
	USART4->CR1 |= (0x1);
}

//发送一个字符
void hal_put_char(const char str)
{
	//1.判断发送数据寄存器是否为空ISR[7]
	//特点：为空才可以发送下一位数据，为满则需要等待
	//读0：满，等待  读1：发送数据
	while(!(USART4->ISR & (0x1 << 7)));
	//2.将发送的内容，赋值给发送给数据寄存器
	USART4->TDR &= 0;
	USART4->TDR = str;
	//3.判断一帧数据是否发送完成 ISR[6]
	while(!(USART4->ISR & (0x1 << 6)));
	//读0:没有发送完成，需要等待  读1：发送完成
}

//接收一个字符
char hal_get_char()
{
	//1.判断接收数据寄存器是否接收到数据 ISR[5]
	while(!(USART4->ISR & (0x1 << 5)));
	//2.将接收数据寄存器中的内容读出来
	char ch = USART4->RDR;
	return ch;
}

//发送一个字符串
void hal_put_string(const char* string)
{
	//判断字符串输入完成标志'\0'
	const char *p = string;
	while(*p != '\0')
	{
		hal_put_char(*p);
		p++;
	}
	//一个字符一个字符进行发送
	hal_put_char('\n');
}

//接收一个字符串
char* hal_get_string()
{
	//循环进行接收
	static char string[32] = {0};
	int i;
	for(i = 0;i < 32; i++)
	{
		string[i] = 0;
	}
	i = 0;
	while(1)
	{
		string[i] = hal_get_char();
		hal_put_char(string[i]);
		if(string[i] == '\r')
		{
			break;
		}
		i++;
	}
	hal_put_char('\n');
	return string;
	//当键盘的回车键按键之后，代表字符串输出完成'\r'
}

 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();
    hal_put_string("----please input--->");
	while(1)
	{
		
		hal_put_char(hal_get_char()+1);
		//hal_put_string(hal_get_string());
	}
	return 0;
}

 hal_put_char(hal_get_char()+1);

hal_put_string(hal_get_string());