Safety issue with Driver Station cRIO mode

[Ben Wolsieffer]

Today we were testing a cRIO based demo robot, using the 2015 driver station software in 2014 protocol mode to control it, when we ran into a major issue that I believe is due to a bug in the DS.

We were having communication issues, which were mainly due to interference from the many networks (>15) in the area. There were times where we lost communication for short periods (~250ms) every couple of seconds, as evidenced by the flickering of the robot code (but not communications, oddly) indicator. Every once in a while, the DS would freeze after this happened (I could not switch tabs or disable/enable the robot), but the voltage readout would continue to be updated. The only way I could fix it was by waiting a few minutes or forcibly killing the DS process.

This wasn't that big a problem until one time when I was driving the robot away from the router and it did not stop when I took my hand off the joystick. The robot did not respond to disable or emergency stop and was eventually stopped by lifting it up and shutting off power.

I was not watching exactly what was happening on the DS, because I was a little preoccupied, but my hypothesis is that this loss of control was not caused by full communication loss, but by the DS freezing and no longer responding to joystick inputs.

While I was driving, the communication probably dropped out a few times (for nearly unnoticeable amounts of time), causing the DS to freeze. Because the voltage still updates when the rest of the DS freezes, the communication seems to be running in a separate thread, so the robot was likely still receiving updates from the DS, but the joystick values were not being updated. I don't believe the loss of control was caused by full communication loss, because in that case the robot should stop, as it always has in the past when we left the range of our wifi network.

Obviously, this is mostly speculation, since I have no idea how the DS works internally, but there it seems almost certain that there is some problem with the DS because it freezes, which should not happen.