Question

I’m writing a program in linux to interface, through serial, with a piece of hardware. The device sends packets of approximately 30-40 bytes at about 10Hz. This software module will interface with others and communicate via IPC so it must perform a specific IPC sleep to allow it to receive messages that it’s subscribed to when it isn’t doing anything useful.

Currently my code looks something like:

while(1){
  IPC_sleep(some_time);
  read_serial();
  process_serial_data();
}

The problem with this is that sometimes the read will be performed while only a fraction of the next packet is available at the serial port, which means that it isn’t all read until next time around the loop. For the specific application it is preferable that the data is read as soon as it’s available, and that the program doesn’t block while reading.

What’s the best solution to this problem?

Answer 1

Store away what you got so far of the message in a buffer of some sort.

If you don’t want to block while waiting for new data, use something like select() on the serial port to check that more data is available. If not, you can continue doing some processing or whatever needs to be done instead of blocking until there is data to fetch.

When the rest of the data arrives, add to the buffer and check if there is enough to comprise a complete message. If there is, process it and remove it from the buffer.