The current DS thread model has some pretty major issues. It makes it difficult to know if all data is from the same remote packet, and if the data changes while the robot loop is running. Additionally, the DS thread is used for a few other things (MotorSafety and State Tracking for EducationalRobot). This also makes sim difficult, as user code has to wait for the thread to know it has new data.
This change completely rethinks how threading works in the driver station model.
First, the DS HAL system receives a new data callback, either from Netcomm or DriverStationSim. Inside the context of this callback, all the low latency data is read and put into a cache. Doing some investigation on the robot side, this is perfectly safe to do, and also ensures a ds packet will not be parsed before we finish reading the current packet data.
After all data is read, the cache is swapped with a 2nd buffer. This buffer just stores the data, none of the HAL DS calls read from this buffer. An event is then fired, stating there is new data ready to go.
Robot code calls HAL_UpdateDSData(). This swaps the 2nd buffer with a 3rd buffer, which always contains the current data. This data will not be updated until HAL_UpdateDSData is called again. Which solves the state problem.
The high level driver station classes have. an updateData() call, which calls HAL_UpdateDSData, and then update button state variables, then data log and update the NT FMS data table (Java also caches across the JNI boundary here, but that could trivially be removed). An extra event provider is provided, allowing other threads to know when this call has been completed.
IterativeRobotBase calls DS.updateData() at the beginning of each loop, and only once per loop. This means all commands will always have the same state.
All of this means there is no longer a DS thread. Everything happens synchronously. This means Sim and testing is easier, as you can just call DriverStationSim.NotifyNewData(), and then DriverStation.UpdateData(), and you can guarantee that all the DriverStation.*** data is up to date.
As for Motor Safety and Educational Robot State Handling, those can all be handled by their own threads. The Educational Thread only needs to run under EducationalRobot, and MotorSafety will only be started if there is a motor safety object enabled.
I started with the output of styleguide#217, then renamed a few classes
to fix compilation.
ntcore's StorageTest needed some manual renaming since it put the Test
word in the middle instead of at the end.
One limitation of wpiformat is test cases that were only named "Test"
were unmodified, and an error was generated. These test cases were
manually given more descriptive names:
* TimedRobotTest mode test cases had "Mode" appended to the name. Java
tests were renamed to match.
* UvAsyncTest and UvAsyncFunctionTest cases were given alternate names
Currently, we have functions like TeleopInit() for running code on mode
entry, but no such functions for running code on mode exit, and it's
cumbersome to add those in user code without making a custom robot
class. This PR adds exit functions to TimedRobot.
Some example use cases include DisabledExit() for operations when the
robot enables (whether that be into teleop, autonomous, or test) and
AutonomousExit() for disabling feedback controllers.
Currently, teams have to make a Notifier to run feedback controllers
more often than the TimedRobot loop period of 20ms (running TimedRobot
more often than this is not advised). This lets users add callbacks to
the main robot loop that run at a user-defined period. This allows
running feedback controllers more often, but does so synchronously with
TimedRobot so there aren't any thread safety issues.
To make the tests reliable, the synchronization in simulation Notifiers
had to be reworked. StepTiming() now waits for all Notifiers to reach
HAL_WaitForNotifierAlarm(), then steps the time, then lets any expired
Notifiers run.
While there, we made some variable names more descriptive and added more
comments.
