语言C串行端口：读取非规范模式

Question

I'm trying to get data from a STM32 Nucleo Board ( but it doesn't really matter ^^ ). I want to get raw data and use the non-canonical mode and everything is set up for. I have set VMIN to 7 to wait until 7 characters are unread and the read wait 7 characters aswell. However my read returns value before to get 7 values and I don't understand why. Do you have any idea ? Am I understanding in a wrong way VMIN ? Thanks for helping me !

My code :

int main(){
int r=-1;
char * device = "/dev/ttyS3";
pt = open(device, O_RDWR | O_NOCTTY | O_SYNC);
if(pt == -1){
    perror("open");
    exit(-1);
}
printf("open : %d\n",pt);
ioctl(pt, I_SRDOPT, RMSGD);
tcgetattr(pt, &old);
atexit(reset_tty);

tcgetattr(pt, &tty); // Get the current attributes of the Serial port

//cfmakeraw(&tty);
tty.c_iflag &= ~(BRKINT | ICRNL | INPCK | ISTRIP | IXON | IXOFF);
tty.c_oflag &= ~(OPOST);
tty.c_cflag |= (CS8);
tty.c_cflag &= ~(CSIZE|PARENB);
tty.c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
tty.c_cc[VMIN] = 7; // wait 7 characters
tty.c_cc[VTIME] = 0;
cfsetispeed(&tty,B9600); // Setting the Baud rate 
cfsetospeed(&tty,B9600);

sleep(1);
r = tcflush(pt, TCIFLUSH);
printf("tcflush : %d\n",r);

r = tcsetattr(pt, TCSANOW, &tty);
printf("tcsetattr : %d\n",r);
int i = 0;
char end[20];

int count = 0;
char line[20];
memset(line,0,sizeof(line));
char forWrite[2]={'A','\0'};

while(count<10){
    r = read(pt ,line,7);
    printf("number of characters : %d\n",r);
    printf("line = %s\n",line);
    //printf("l = %c\n",line[0]);
    count++;
    memset(line,0,sizeof(line));
    printf("\n");
}
return 0;
}

My output :

number of characters : 1
line =

number of characters : 2
line = 12

number of characters : 2
line = 33

number of characters : 5
line = 456ab

number of characters : 5
line = cdefg

number of characters : 1
line = a

number of characters : 4
line = bcde

number of characters : 2
line = fg

number of characters : 1
line = 1

number of characters : 3
line = 233

And i'm sending from my STM32 "abcdefg" and then "1234567"

EDIT : the code and the output I posted was matching, I have just changed my prints in order to be clearer for you...and I failed ^^, It's edited now thx :)

Answer 1

我不知道这是怎么回事，但是“慢速”设备（例如串行端口）上的read() （和其他I / O接口）将在等待完成时收到信号后立即返回。