linux 串口编程 用read函数读取数据被截断 怎样一次读完

通常编写串口软件，需要设置一个缓冲来保存读取的数据，然后进行协议分析。不管你设置读取多长的数据，由于串口发送是有时延的，而你读数据的计算机无法知道发送方何时发送完毕再开始调用read，故只能采取读进缓冲中，每次读完，分析一下，看看是否读完。

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[0134m", 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[0131m", 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

}

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