【STM32MP135F-DK测评】编写串口应用程序

上一篇（https://bbs.21ic.com/icview-3360172-1-1.html）中已经完成了UART的设备树的配置和编译，以及使用shell脚本进行简单的UART的数据的收发测试，这一篇将编写应用程序来发送UART数据，同时打印接收到的UART数据。
本篇将使用termios 结构体以及相关的api来实现对串口的设置、数据的写入和读取。

1、编写应用代码
先是调用serial_open函数对UART硬件进行初始化，其中设备名（串口号）需要作为参数传入，其它参数已经被程序指定死了，不可传入。默认波特率9600，8N1。
初始化完成后，进入while（1）循环中，循环发送字符串Hello STM32MP135F-DK,同时查看串口是否有消息接收到，若有则通过控制台打印出来。
uart.c源代码如下：

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#include <stdio.h> /* Standard input/output */



#include <fcntl.h> /* File control definitions */



#include <string.h>



#include <stdlib.h>



#include <termio.h> /* POSIX terminal control definitions */



#include <sys/time.h> /* Time structures for select() */



#include <unistd.h> /* POSIX Symbolic Constants */



#include <assert.h>



#include <errno.h> /* Error definitions */



#include <sys/mman.h>



#define CMSPAR 010000000000



#define SERIAL_FLUSH_TX1



#define SERIAL_FLUSH_RX2



#define SERIAL_PARITY_NO 0



#define SERIAL_PARITY_ODD 1



#define SERIAL_PARITY_EVENT 2



#define SERIAL_PARITY_MARK 3



#define SERIAL_PARITY_SPACE 4



#define SERIAL_STOPBIT_ONE 1



#define SERIAL_STOPBIT_TWO 2



static int serial_fd = -1;



struct termios old_tios;



static void serial_print_buf(unsigned char *buf,int len) /* 打印输出 */



{



int i;



for(i=0;i<len;i++)



printf("%02X ",buf[i]);



printf("\n");



}



char *get_serial_dev_name(char *serial_name) /* 获取串口名称 */



{



if (strcasecmp(serial_name, "/dev/ttySTM1") == 0)



return serial_name;



else



return "NULL";



}



static int termios_init(struct termios *tios,int baud,int parity,int data_bits,int stop_bits) //串口 传入波特率，校验位，数据位，停止位。



{



speed_t baud_rate;



if (tios == NULL)



return -1;



tios->c_line = 0;



tios->c_cc[VMIN ] = 0;



tios->c_cc[VTIME] = 0;



/* configure the input modes... */



tios->c_iflag = IGNBRK | IGNPAR | INPCK;



/* configure the output modes... */



tios->c_oflag = 0; /* enable implementation-defined output processing */



/* configure the control modes... */



tios->c_cflag = CREAD | CLOCAL;



if (data_bits == 5) //对传入的数据位进行判断



tios->c_cflag |= CS5;



else if (data_bits == 6)



tios->c_cflag |= CS6;



else if (data_bits == 7)



tios->c_cflag |= CS7;



else if (data_bits == 8)



tios->c_cflag |= CS8;



else



return -1;



if (stop_bits == 1)//对传入的停止位进行判断



tios->c_cflag &=~ CSTOPB;



else if (stop_bits == 2)



tios->c_cflag |= CSTOPB;



else



return -1;



if(parity == 0)//校验位: 0:无校验 1:奇校验 2:偶校验 3:mark parity 4:space parity



{ /* none */



tios->c_cflag &=~ PARENB;



tios->c_cflag &=~ PARODD;



}



else if(parity == 2)



{ /* even */



tios->c_cflag |= PARENB;



tios->c_cflag &=~ PARODD;



}



else if(parity == 1)



{ /* odd */



tios->c_cflag |= PARENB;



tios->c_cflag |= PARODD;



}



else if (parity == 3)/* 2008.12.17 add for support mark and space parity */



{



/* mark */



tios->c_cflag |= PARENB;



tios->c_cflag |= CMSPAR;



tios->c_cflag |= PARODD;



}



else if (parity == 4)



{



/* space */



tios->c_cflag |= PARENB;



tios->c_cflag |= CMSPAR;



}



else



return -1;



/* configure the local modes... */



tios->c_lflag = 0; /* enable implementation-defined input processing */



/* Set the baud rate */



switch(baud)//对传入的波特率进行判断



{



case 110:



baud_rate = B110;



break;



case 300:



baud_rate = B300;



break;



case 600:



baud_rate = B600;



break;



case 1200:



baud_rate = B1200;



break;



case 2400:



baud_rate = B2400;



break;



case 4800:



baud_rate = B4800;



break;



case 9600:



baud_rate = B9600;



break;



case 19200:



baud_rate = B19200;



break;



case 38400:



baud_rate = B38400;



break;



case 57600:



baud_rate = B57600;



break;



case 115200:



baud_rate = B115200;



break;



case 230400:



baud_rate = B230400;



break;



case 460800:



baud_rate = B460800;



break;



case 576000:



baud_rate = B576000;



break;



case 921600:



baud_rate = B921600;



break;



default:



return -1;



}



if ((cfsetispeed(tios, baud_rate) < 0) ||(cfsetospeed(tios, baud_rate) < 0))



return -1;



return 0;



}



//return serial fd, error return -1



int serial_open(char *serial_name, int baud,int parity,int data_bits,int stop_bits,int timeout) //打开串口



{



struct termios settings;



int fd;



char *serial_dev_name;



if (serial_fd >= 0)



return 0;



if (termios_init(&settings, baud,parity,data_bits,stop_bits) < 0)



return 0;



serial_dev_name = get_serial_dev_name(serial_name);



if (serial_dev_name == NULL)



{



fprintf(stderr, "invalid serial name:%s\n", serial_name);



return 0;



}



if((fd = open(serial_dev_name, O_RDWR | O_NOCTTY | O_NDELAY))< 0)



return 0;



if(tcgetattr(fd, &old_tios) < 0)



{



close(fd);



return 0;



}



if(tcsetattr(fd, TCSANOW, &settings) < 0)



{



close(fd);



return 0;



}



serial_fd = fd;



return 1;



}



int serial_close() //关闭串口



{



if (serial_fd < 0)



return 0;



tcsetattr(serial_fd, TCSANOW, &(old_tios));



close(serial_fd);



serial_fd = -1;



return 1;



}



int serial_flush(int flag)



{



if (serial_fd < 0)



return 0;



if (flag == SERIAL_FLUSH_TX)



tcflush(serial_fd,TCOFLUSH);



else if (flag == SERIAL_FLUSH_RX)



tcflush(serial_fd,TCIFLUSH);



else if (flag == (SERIAL_FLUSH_RX|SERIAL_FLUSH_TX) )



tcflush(serial_fd,TCIOFLUSH);



return 1;



}



int serial_write(char *buf,size_t size) //串口写入数据



{



int writesize = 0;



writesize = write(serial_fd,buf,size);



//printf("serial write: length=%d, packet: ",writesize);



//serial_print_buf(buf,writesize);



return writesize;



}



int serial_read(char *buf,size_t size) //串口读取数据



{



int readsize = 0;



if (size<=0)



return 0;



readsize = read(serial_fd,buf,size);



printf("serial read: length=%d, packet: ",readsize);



serial_print_buf(buf, readsize);



return readsize;



}



//return 1: poll ok, 0: timeout, -1: error



int serial_poll(int timeout)



{



int fd = serial_fd;



fd_set rfds;



struct timeval tv;



int sel_res;



FD_ZERO(&rfds);



FD_SET(fd, &rfds);



tv.tv_sec = timeout/1000;



tv.tv_usec = (timeout % 1000)*1000;



return select(fd + 1, &rfds, NULL,NULL,&tv);



}



int main(int argc, char *argv[])



{



int fd;



char send_buffer[100] = "Hello STM32MP135F-DK\r\n";



char recv_buffer[100];



int i, ret;



if (argc != 2) //需要传入串口对应的设备名



{



fprintf(stderr, "usage:serialtest com_port\n");



return -1;



}



ret = serial_open(argv[1], 9600, SERIAL_PARITY_NO, 8, SERIAL_STOPBIT_ONE, 1000); //调用上面封装好的打开串口函数 传入设备名，波特率，校验位，数据位，停止位以及超时时间



if (ret == 0)//打开失败



{



fprintf(stderr, "open serial failed\n");



return -1;



}



/*



for(i=0; i<20; i++)



{



send_buffer[i] = i;



}



*/



while(1)



{



serial_write(send_buffer, strlen(send_buffer)); //写入数据



//read



while (serial_poll(1000)>0)//当另一端传入数据时会接收到数据



{



serial_read(recv_buffer, sizeof(recv_buffer));



}



}



serial_close();



return 0;



}

Makeifle文件：

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uart:uart.c



$(CC) -Iinclude -o uart uart.c



clean:



rm *.o uart

2、编译应用程序
使用make命令来进行编译

编译之前记得source一下编译环境

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source SDK/environment-setup-cortexa7t2hf-neon-vfpv4-ostl-linux-gnueabi

编译完成后会生成uart的可执行文件

将uart可执行文件上传到开发板后，进入到开发板终端执行uart程序：

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root@stm32mp1:~# ./uart /dev/ttySTM1

此时，串口助手上已经能看到开发板发出来的消息了：

然后，通过串口助手发送消息给开发板，开发板会将收到的消息打印在终端上：
串口终端发送字符串1234，开发板终端打印的消息如下：

以上，可以用看出得到的结果符合程序预期的运行结果，测试完成。