Question

I’ve got a two controllers one with uclinux, second without any os. They are connected by serial port. I check that new message received with select function. Message length might be different and controller without os sends message per bytes. So, there is a possibility that one controller does not send whole message and select function returns that new message is available. After that I will receive incorrect message.
How I can prevent this situation?

Answer 1

The select function will only tell you that you can read at least one byte without blocking. The message sent on the serial port needs to either have a predefined header that contains the total length of the message, or a special end-of-message marker.

When select says you can read, you read as many bytes as you can and put them in a buffer. If the message is not complete you go back to wait for more data with select. When more data arrives you continue append to the buffer. When a complete message is received you process it.