Button on robot frame function

[cristhoper]

Overview

Relevant issues:
#5
Opentrons/opentrons#531

The work made it, was based on the scheme of the following image.

The script conf_button.py has the implementation of the states. Also, there is a couple of method to incorporate external functions that runs at startup and pause states.
The example test_button.py, shows how to use the callbacks and set states from GUI.

Note: The double tap, was not implemented.

Relevant Links

https://github.com/cristhoper/hack-a-tron.git

Next iteration possibilities

The implementation with while True is not a strong solution. Is better try to implement callbacks and interrupts. But to do that, the opentrons.drivers.rpi_drivers needs to be implemented with low-level APIs, because the implementation with Linux Kernel is not the fastest and the interrupts are not completely supported.

[nadimest]

Any reason why this hasn't been implemented in recent firmware versions? Anything I can do to help? Users are asking me for an emergency stop button (pause is fine) and I was thinking on implementing a similar solution.

[ColtonGarelli]

A killswitch would be nice. It'd be great if we could cancel a protocol using the button. We've lost usb connection mid-run and haven't been able to stop the robot which resulted in frantically removing items from the deck to avoid samples getting messed up.