So now we know what is going on with the slave. We have some bits to set that tell our master what we're up to and how we're doing. In turn, the master will set some bits to control how we traverse our possible states. The master is another beast entirely but we're not going to worry about today so please...

Now that we know our basics, let's dig into some code!  Since we like to get things done quickly, we'll be working with Python and pyserial. We'll start with defining an Acceptor class that will hold the state of our virtual BA (bill acceptor).

We're going to want to track the following values:

• State
• Event(s)
• Bill Value
• RS-232 Fields

Code doesn't look great on here so I'll just be linking to my Github Soft Bill Project and then explaining what is going on. We'll start with the Acceptor class definition. On a sidenote, there are two things that I really dislike in code: flags as globals and unnecessary multidimensional arrays. Here we track our internal state in a single object to avoid having a whole bunch of globals to track. This object is then passed by the main method into the worker thread so we are sitting pretty.
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Threads!

That's right, we are working with a background thread so we can leave our virtual BA's serial TxRx alone while we arbitrarily modify its state and observe how the master behaves. For now we are not going to worry about race conditions and other multithreading headaches. The thread magic is super simple. Spin up a non-daemon thread, pass the proper arguments, then enter our STDIN loop. Please be sure to set the daemon mode to false so as to avoid leaving the serial port resource open. See the code for a link to the quoted documentation explaining why.

Keyboard Input

So now we have a background thread and STDIN (keyboard input) thread. How do we get our input into the virtual BAs? We've defined a command parser method to handle the interpretation and state modification for us. The last portion is to actually use the data, build our packet, and send it on its way. All the while listening to our master of course. This is all handled in the method we passed into our background thread called serial_runner.

Eventually we will want to incorporate this state machine with out fancy little emulator.</p>

Wrapping Up

That's basically it! This is still a work in progress and you may have noticed that our slave does not do much besides report events. There is still a system that needs to be built for mocking the bill movement timing as well as compensation for bad/damaged/missing packets. Feel free to ask questions, share your code, or poke holes in anything that I have said. 

 

Happy coding!
The Pyramid Software Team