Question

linux的串口编程。read（）读不出回车键

linux的串口编程。串口的输入输出都是原始模式，串口文件描述符设为非阻塞，当用read()函数去读串口的fd时，任何一个字符都可以读出来，但就是回车键读不出来，不知道哪里出了问题？
答案我找见了，我从网上摘的初始化串口的程序并不完整，只是初始化了波特率，数据位，奇偶校验，停止位，硬软件流控制，其他的并没有初始化。
stty -a < /dev/ttyS1 可以查看当前串口的属性，先用minicom打开串口，再用这个命令查看串口属性，然后按照这个属性完善了我的串口初始化部分。
我是没有将 IGNCR 设置为无效，结果他忽略了 <CR> ，所以按回车键就无效了。

Answer 1

这有个友善的串口例程，参考下吧，用gcc编译可以在linux下用
# include <stdio.h>
# include <stdlib.h>
# include <termio.h>
# include <unistd.h>
# include <fcntl.h>
# include <getopt.h>
# include <time.h>
# include <errno.h>
# include <string.h>

int CommFd, TtyFd;

static void Error(const char *Msg)
{
fprintf (stderr, "%s\n", Msg);
fprintf (stderr, "strerror() is %s\n", strerror(errno));
exit(1);
}
static void Warning(const char *Msg)
{
fprintf (stderr, "Warning: %s\n", Msg);
}

static int SerialSpeed(const char *SpeedString)
{
int SpeedNumber = atoi(SpeedString);
# define TestSpeed(Speed) if (SpeedNumber == Speed) return B##Speed
TestSpeed(1200);
TestSpeed(2400);
TestSpeed(4800);
TestSpeed(9600);
TestSpeed(19200);
TestSpeed(38400);
TestSpeed(57600);
TestSpeed(115200);
TestSpeed(230400);
Error("Bad speed");
return -1;
}

static void PrintUsage(void)
{

fprintf(stderr, "comtest - interactive program of comm port\n");
fprintf(stderr, "press [ESC] 3 times to quit\n\n");

fprintf(stderr, "Usage: comtest [-d device] [-t tty] [-s speed] [-7] [-c] [-x] [-o] [-h]\n");
fprintf(stderr, " -7 7 bit\n");
fprintf(stderr, " -x hex mode\n");
fprintf(stderr, " -o output to stdout too\n");
fprintf(stderr, " -c stdout output use color\n");
fprintf(stderr, " -h print this help\n");
exit(-1);
}

static inline void WaitFdWriteable(int Fd)
{
fd_set WriteSetFD;
FD_ZERO(&WriteSetFD);
FD_SET(Fd, &WriteSetFD);
if (select(Fd + 1, NULL, &WriteSetFD, NULL, NULL) < 0) {
Error(strerror(errno));
}

}

int sendUart(char c)
{
WaitFdWriteable(CommFd);
return write(CommFd, &c, 1);
}

char recUart()
{
char c='\0';
if (FD_ISSET(CommFd, &ReadSetFD))
{
if(read(CommFd, &c, 1) == 1) return c;
else printf("No data to receive.\n");
}
}

int main(int argc, char **argv)
{
struct termios TtyAttr;
struct termios BackupTtyAttr;

int DeviceSpeed = B115200;
int TtySpeed = B115200;
int ByteBits = CS8;
const char *DeviceName = "/dev/ttyS0";
const char *TtyName = "/dev/tty";
int OutputHex = 0;
int OutputToStdout = 0;
int UseColor = 0;

printf("Now we start.\n");
opterr = 0;
for (;;) {
int c = getopt(argc, argv, "d:s:t:7xoch");
if (c == -1)
break;
switch(c) {
case 'd':
DeviceName = optarg;
break;
case 't':
TtyName = optarg;
break;
case 's':
if (optarg[0] == 'd') {
DeviceSpeed = SerialSpeed(optarg + 1);
} else if (optarg[0] == 't') {
TtySpeed = SerialSpeed(optarg + 1);
} else
TtySpeed = DeviceSpeed = SerialSpeed(optarg);
break;
case 'o':
OutputToStdout = 1;
break;
case '7':
ByteBits = CS7;
break;
case 'x':
OutputHex = 1;
break;
case 'c':
UseColor = 1;
break;
case '?':
case 'h':
default:
PrintUsage();
}
}
if (optind != argc)
PrintUsage();

CommFd = open(DeviceName, O_RDWR, 0);
if (CommFd < 0)
Error("Unable to open device");
if (fcntl(CommFd, F_SETFL, O_NONBLOCK) < 0)
Error("Unable set to NONBLOCK mode");

memset(&TtyAttr, 0, sizeof(struct termios));
TtyAttr.c_iflag = IGNPAR;
TtyAttr.c_cflag = DeviceSpeed | HUPCL | ByteBits | CREAD | CLOCAL;
TtyAttr.c_cc[VMIN] = 1;

if (tcsetattr(CommFd, TCSANOW, &TtyAttr) < 0)
Warning("Unable to set comm port");

TtyFd = open(TtyName, O_RDWR | O_NDELAY, 0);
if (TtyFd < 0)
Error("Unable to open tty");

TtyAttr.c_cflag = TtySpeed | HUPCL | ByteBits | CREAD | CLOCAL;
if (tcgetattr(TtyFd, &BackupTtyAttr) < 0)
Error("Unable to get tty");

if (tcsetattr(TtyFd, TCSANOW, &TtyAttr) < 0)
Error("Unable to set tty");

for (;;) {
unsigned char Char = 0;
fd_set ReadSetFD;

void OutputStdChar(FILE *File) {
char Buffer[10];
int Len = sprintf(Buffer, OutputHex ? "%.2X " : "%c", Char);
fwrite(Buffer, 1, Len, File);
}

FD_ZERO(&ReadSetFD);

FD_SET(CommFd, &ReadSetFD);
FD_SET( TtyFd, &ReadSetFD);
# define max(x,y) ( ((x) >= (y)) ? (x) : (y) )
if (select(max(CommFd, TtyFd) + 1, &ReadSetFD, NULL, NULL, NULL) < 0) {
Error(strerror(errno));
}
# undef max

if (FD_ISSET(CommFd, &ReadSetFD)) {
while (read(CommFd, &Char, 1) == 1) {

WaitFdWriteable(TtyFd);
if (write(TtyFd, &Char, 1) < 0) {
Error(strerror(errno));
}
if (OutputToStdout) {
if (UseColor)
fwrite("\x1b[01;34m", 1, 8, stdout);
OutputStdChar(stdout);
if (UseColor)
fwrite("\x1b[00m", 1, 8, stdout);
fflush(stdout);
}
}
}

if (FD_ISSET(TtyFd, &ReadSetFD)) {
while (read(TtyFd, &Char, 1) == 1) {
static int EscKeyCount = 0;
WaitFdWriteable(CommFd);
if (write(CommFd, &Char, 1) < 0) {
Error(strerror(errno));
}
if (OutputToStdout) {
if (UseColor)
fwrite("\x1b[01;31m", 1, 8, stderr);
OutputStdChar(stderr);
if (UseColor)
fwrite("\x1b[00m", 1, 8, stderr);
fflush(stderr);
}

if (Char == '\x1b') {
EscKeyCount ++;
if (EscKeyCount >= 3)
goto ExitLabel;
} else
EscKeyCount = 0;
}
}

}

ExitLabel:
if (tcsetattr(TtyFd, TCSANOW, &BackupTtyAttr) < 0)
Error("Unable to set tty");

return 0;
}