我有以下C程序:
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
int main()
{
int fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NONBLOCK);
if(fd < 0)
{
perror("Could not open device");
}
printf("Device opened\n");
struct termios options;
tcgetattr(fd, &options);
cfmakeraw(&options);
cfsetispeed(&options, B19200);
cfsetospeed(&options, B19200);
tcsetattr(fd, TCSANOW, &options);
char txpacket[] = {0x23, 0x06, 0x00, 0x00, 0xdd, 0xf9};
ssize_t written = write(fd, txpacket, sizeof(txpacket));
printf("Written %d bytes\n", written);
printf("Starting to wait for target to respond\n");
while(1)
{
fd_set readset;
FD_ZERO(&readset);
FD_SET(fd, &readset);
int nCount = select(fd + 1, &readset, NULL, NULL, NULL);
if(nCount > 0)
{
if(FD_ISSET(fd, &readset))
{
int i;
char buffer[128];
ssize_t bytesread = read(fd, buffer, sizeof(buffer));
printf("Received %d bytes\n", bytesread);
for(i = 0; i < bytesread; i++)
{
printf(" %02x", buffer[i]);
}
}
}
}
}
该程序打开串口设备/dev/ttyS0,向其写入一系列数据并开始等待响应。输出如下所示:
Device opened
Written 6 bytes
Starting to wait for target to respond
Received 0 bytes
Received 0 bytes
Received 0 bytes
Received 0 bytes
Received 0 bytes
Received 0 bytes
...
应用程序消耗了100%的CPU。尽管目标硬件实际上传输数据,但我无法接收任何数据。
问题出在哪里?
open()
返回的新文件描述符不一定与您刚关闭的那个号码相同,因此,如果旧文件描述符在其他地方记录(例如在fd_set
中),则需要将其删除并用新打开的一个替换它。 - caf