[英]Linux Reading Data from UART
我想从UART读取数据,我按照本教程操作 ,写功能按预期工作,但是读功能出现问题:
这是uart_init函数:
void uart_init()
{
printf("\n +----------------------------------+");
printf("\n | Serial Port Write |");
printf("\n +----------------------------------+");
/*------------------------------- Opening the Serial Port -------------------------------*/
fd = open("/dev/ttyUSB0",O_RDWR | O_NOCTTY| O_SYNC); /* !!blocks the read */
/* O_RDWR Read/Write access to serial port */
/* O_NOCTTY - No terminal will control the process */
/* O_NDELAY -Non Blocking Mode,Does not care about- */
/* -the status of DCD line,Open() returns immediatly */
if(fd == -1) /* Error Checking */
printf("\n Error! in Opening ttyUSB0 ");
else
printf("\n ttyUSB0 Opened Successfully ");
/*---------- Setting the Attributes of the serial port using termios structure --------- */
struct termios SerialPortSettings; /* Create the structure */
tcgetattr(fd, &SerialPortSettings); /* Get the current attributes of the Serial port */
cfsetispeed(&SerialPortSettings,B19200); /* Set Read Speed as 19200 */
cfsetospeed(&SerialPortSettings,B19200); /* Set Write Speed as 19200 */
SerialPortSettings.c_cflag &= ~PARENB; /* Disables the Parity Enable bit(PARENB),So No Parity */
SerialPortSettings.c_cflag &= ~CSTOPB; /* CSTOPB = 2 Stop bits,here it is cleared so 1 Stop bit */
SerialPortSettings.c_cflag &= ~CSIZE; /* Clears the mask for setting the data size */
SerialPortSettings.c_cflag |= CS8; /* Set the data bits = 8 */
SerialPortSettings.c_cflag &= ~CRTSCTS; /* No Hardware flow Control */
SerialPortSettings.c_cflag |= CREAD | CLOCAL; /* Enable receiver,Ignore Modem Control lines */
SerialPortSettings.c_iflag &= ~(IXON | IXOFF | IXANY); /* Disable XON/XOFF flow control both i/p and o/p */
SerialPortSettings.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG); /* Non Cannonical mode */
SerialPortSettings.c_oflag &= ~OPOST;/*No Output Processing*/
/* Setting Time outs */
SerialPortSettings.c_cc[VMIN] = 10; /* Read at least 10 characters */
SerialPortSettings.c_cc[VTIME] = 0; /* Wait indefinetly */
if((tcsetattr(fd,TCSANOW,&SerialPortSettings)) != 0) /* Set the attributes to the termios structure*/
printf("\n ERROR ! in Setting attributes");
else
printf("\n BaudRate = 19200 \n StopBits = 1 \n Parity = none");
}
接收功能:
void uart_receive()
{
char read_buffer[32]; /* Buffer to store the data received */
int bytes_read = 0; /* Number of bytes read by the read() system call */
int i = 0;
bytes_read = read(fd,&read_buffer,10); /* Read the data */
printf("\n\n Bytes Rxed %d", bytes_read); /* Print the number of bytes read */
printf("\n\n ");
for(i=0;i<bytes_read;i++) /*printing only the received characters*/
printf("%c",read_buffer[i]);
printf("\n +----------------------------------+\n\n\n");
}
主要功能:
void main(void)
{
uart_init();
/*------------------------------- Write data to serial port -----------------------------*/
//uart_write_commande(write_buffer); //Write function works well
uart_receive();
close(fd);/* Close the Serial port */
}
编辑
我执行程序并等待在UART中接收数据字节,我使用UART发送数据,但读取功能一直处于阻塞状态。
我正在使用带有Ubunutu 14.04的虚拟机,但不确定使用仿真的UART会在接收期间引起问题。
读取功能有错误
bytes_read = read(fd,&read_buffer,10); /* Read the data
应该
bytes_read = read(fd,read_buffer,10); /* Read the data
您的程序挂在read()系统调用中,因为它被阻止等待行终止符。
您尝试使用以下语句将端口配置为非规范模式
SerialPortSettings.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG); /* Non Cannonical mode
但是该操作是在错误的termios元素上进行的。
所述ICANON属性是lflag元件(而不是IFLAG)的一部分。 (此错误源自您引用的教程!)
因此,您的程序正在执行阻止规范读取。
有一个方便的termios函数可用于配置非规范模式:
cfmakeraw() sets the terminal to something like the "raw" mode of the old
Version 7 terminal driver: input is available character by
character, echoing is disabled, and all special processing of
terminal input and output characters is disabled. The terminal
attributes are set as follows:
termios_p->c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP
| INLCR | IGNCR | ICRNL | IXON);
termios_p->c_oflag &= ~OPOST;
termios_p->c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
termios_p->c_cflag &= ~(CSIZE | PARENB);
termios_p->c_cflag |= CS8;
无论出于何种原因,您的read()函数都可能被阻止。 这是关于从串行端口读取的讨论 ,包括阻止/取消阻止设置的代码。
也有可能没有数据在传输,导致什么也没有被读取。 如果无法访问硬件设置,那么如果没有关于所看到内容的非常具体的信息,则很难走得更远。
此外,除了正确传递read_buffer(另一个答案)外,至少还有两个其他方面可以改进:
1)在使用前检查read
的返回:
bytes_read = read(fd,&read_buffer,10); /* Read the data*/
if(bytes_read > 0)
{
...
}
2)变更:
for(i=0;i<bytes_read;i++) /*printing only the received characters*/
printf("%c",read_buffer[i]);
至:
//after successful read:
read_buffer[bytes_read]=0;//place null termination after last character read.
printf("%s",read_buffer);//note format specifier
这将打印读取的字符数,而不循环。
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