头文件：

 1 #ifndef __UART4_H__                               2 #define __UART4_H__                               3                                                   4 #include "../common/include/stm32mp1xx_rcc.h"     5 #include "../common/include/stm32mp1xx_gpio.h"    6 #include "../common/include/stm32mp1xx_uart.h"    7                                                   8 //UART4串口初始化                                 9 void hal_uart_init(void);                         
10                                                   
11 //发送一个字符                                    
12 void hal_put(const char str);                     
13                                                   
14 //发送一个字符串                                  
15 void hal_put_string(const char* string);          
16                                                   
17 //接收一个字符                                    
18 char get_char(void);                              
19                                                   
20 //接收一个字符串                                  
21 char* get_string(void);                           
22                                                   
23 #endif                                            

源文件：

  1 #include "uart4.h"2 3 //UART4串口初始化4 void hal_uart_init(void)5 {6     /********** RCC 相关寄存器初始化***********/7     RCC->MP_AHB4ENSETR |= (0x1<<1); //使能GPIOB组控制器8     RCC->MP_AHB4ENSETR |= (0x1<<6); //使能GPIOG组控制器9     RCC->MP_APB1ENSETR |= (0x1<<16); //使能UART4组控制器10 11     /********** GPIO 相关寄存器初始化***********/12     GPIOB->MODER &= (~(0x3<<4)); //设置PB2引脚为复用功能13     GPIOB->MODER |= (0x2<<4);14     GPIOG->MODER &= (~(0x3<<22)); //设置PG11引脚为复用功能15     GPIOG->MODER |= (0x2<<22);16 17     GPIOB->AFRL &= (~(0xf<<8)); //设置PB2引脚复用功能为 URAT4_RX18     GPIOB->AFRL |= (0x1<<11);19     GPIOG->AFRH &= (~(0xf<<12)); //设置PG11引脚复用功能为 URAT4_TX20     GPIOG->AFRH |= (0x6<<12);21 22     /********** UART4 相关寄存器初始化***********/23     //1.USART_CR1：设置数据位宽度，以及对应的控制器使能(UART控制器使能，发送寄存器使能，接收寄存器使能)24     USART4->CR1 &= (~(0x1<<28));25     USART4->CR1 &= (~(0x1<<12));26     USART4->CR1 &= (~(0x1<<15));27     USART4->CR1 &= (~(0x1<<10));28     USART4->CR1 |= (0x1<<3);29     USART4->CR1 |= (0x1<<2);30     USART4->CR1 |= 0x1;31 32     //2.USART_CR2：设置串口停止位33     USART4->CR2 &= (~(0x3<<12));34 35     //3.USART_BRR：设置串口波特率36     USART4->BRR = 0x22b;37 38     //7.USART_PRESC：设置串口分频器39     USART4->PRESC &= (~0xf);40 41 }42 43 //发送一个字符44 void hal_put(const char str)45 {46     //判断发送数据寄存器是否有数据47     while(!(USART4->ISR & (0x1<<7))); //位7为1时，可以发送数据，跳出循环48 49 //  USART4->TDR &= (~(0xff));50     USART4->TDR = str;51 52     //判断发送数据寄存器是否发送完成53     while(!(USART4->ISR & (0x1<<6)));//位6为1时，发送数据完成，跳出循环54 }55 56 //发送一个字符串57 void hal_put_string(const char* string)                                                                                                58 {59     //判断字符串结束标志60     while('\0' != *string)61     {62         hal_put(*string);63         string++;64     }65 }66 67 //接收一个字符68 char get_char(void)69 {70     //判断接收数据寄存器是否接收到数据71     while(!(USART4->ISR & (0x1<<5))); //位5为1时，可以读取数据，跳出循环72     return (char)USART4->RDR;73 }74 75 char buf[128] = "";76 //接收一个字符串77 char* get_string(void)78 {79     //键盘的回车键按下，对应的字符'\r'80     int i;81     for(i=0; i<(sizeof(buf)-1); i++)82     {83         buf[i] = get_char();84         hal_put(buf[i]);85 86         if('\r' == buf[i])87         {88             break;89         }90     }91     buf[i] = '\0';92     hal_put('\n');93 94     return buf;95 96 }97 

主函数测试：

 1 #include "uart4.h"2 3 extern void printf(const char *fmt, ...);4 void delay_ms(int ms)5 {6     int i,j;7     for(i = 0; i < ms;i++)8         for (j = 0; j < 1800; j++);9 }
10 
11 
12 int main()
13 {
14     hal_uart_init();
15     printf("ARM,YES!!!\n");
16     while(1)
17     {
18         //hal_put(get_char()+1);              
19         hal_put_string(get_string());
20     }
21     return 0;
22 }

实验现象：