Parse and read data frame in C?
- by user253656
I am writing a program that reads the data from the serial port on Linux.
The data are sent by another device with the following frame format:
|start | Command | Data | CRC | End |
|0x02 | 0x41 | (0-127 octets) | | 0x03|
----------------------------------------------------
The Data field contains 127 octets as shown and octet 1,2 contains one type of data; octet 3,4 contains another data. I need to get these data
I know how to write and read data to and from a serial port in Linux, but it is just to write and read a simple string (like "ABD")
My issue is that I do not know how to parse the data frame formatted as above so that I can:
get the data in octet 1,2 in the Data field
get the data in octet 3,4 in the Data field
get the value in CRC field to check the consistency of the data
Here the sample snip code that read and write a simple string from and to a serial port in Linux:
int writeport(int fd, char *chars) {
int len = strlen(chars);
chars[len] = 0x0d; // stick a <CR> after the command
chars[len+1] = 0x00; // terminate the string properly
int n = write(fd, chars, strlen(chars));
if (n < 0) {
fputs("write failed!\n", stderr);
return 0;
}
return 1;
}
int readport(int fd, char *result) {
int iIn = read(fd, result, 254);
result[iIn-1] = 0x00;
if (iIn < 0) {
if (errno == EAGAIN) {
printf("SERIAL EAGAIN ERROR\n");
return 0;
} else {
printf("SERIAL read error %d %s\n", errno, strerror(errno));
return 0;
}
}
return 1;
}
Does anyone please have some ideas?
Thanks all.
