Can't read more than eight bytes from serial port

Question

I'm working in c programming language under Linux, trying to create a communication application with serial port. The program is sending data to a serial port and reading received data from a microcontroller. The received data could reach any number of bytes between 10 and 64 but no more and no less. I use the following code to read and write data:

unsigned char send_bytes[] = { 0x1, 0x6, 0x2, 0xAA, 0x2, 0x3, 0xB8, 0x4 };

int w = write(fd, send_bytes, sizeof(send_bytes)); // send

char buffer[64];

int r = read(fd, buffer, sizeof(buffer)); //read data

My problem is that r never gets more than 8 bytes of data. Does anyone know why is this the case?

Thanks in advance.

int read, Use different name for function and variable. Don't mix them. — Don't You Worry Child
Sorry they are not named the same. I wrote it here like that, it's fixed now. — user2081328
Try adding subsequent read functions and see what they return. — Don't You Worry Child
You probably need to show your code for the open() and initialization of the serial port. Also, performing syscalls in the variable declarations in not good practice. — sawdust

unwind unwind · Accepted Answer · 2014-02-27T10:35:49

Perhaps your operating system is only providing 8 bytes of serial port buffering, so it "favors" to deliver incoming data in chunks of 8 bytes.

Repeat the read for as long as it has data available. You can use select() for this on systems where it's available.

Also, since the other end is a microcontroller which might be slower than your workstation by a large margin, perhaps the data simply isn't available yet when you do the read(). That's another reason to try again, of course.

Can't read more than eight bytes from serial port

1 Answers