First step -- a chat interface

The first thing we need is a way to communicate between python and the arduino over the serial port.

Python side

The `pyserial` library makes things easy here.

The `timeout` keyword is a key element here. That defines how long `readlines` will wait for input before returning. If you set it to 0, it will return whatever it finds immediately. The problem with that approach is that we're going to be calling this function over and over again in an infinite loop. I suspect a smaller number of calls with a small delay will end up being more efficient than a much larger number of calls with a near-zero delay. That's something to test layer.

The `write` function actually writes immediately and returns ("non-blocking").

The Arduino side

The arduino needs something to say. Let's have it report the time every second. Also, let's have it acknowledge any chat it receives, simply by echoing back whatever it hears.

The actual `receive_chat` function resides in a library.

Things are more complicated here than in Python because we have only low-level functions available. Whenever there are new characters available, we add them to a global variable `receive_buffer`. It has to be global because it needs to persist over many calls to this function.

Once the buffer gets to a newline, it stops taking characters and returns the line it received. It also echoes it on the serial port so that Python knows its message was received.

What if multiple lines are waiting to be received? This will only return the first one. This is easier than coding up a linked list of multiple commands. It also means that other things have a chance to run on the rest of the update cycle.



Now the arduino can communicate with Python. But how does Python interact with the user? The user might be a real person, or it might be another Python script, for instance one controlling the state machine. The next post will cover the methods by which the user can read what the arduino is saying, and type in responses.