Velocity PID Programming: Terms dependent on time

[kenfox]

Originally Posted by Ether

1) how many layers of code are wrapped around each of these timers

Generally 2 layers + the hardware or whatever the black box routines require. WPILib -> ChipObject (FPGA timer), WPILib -> NI (PPC timer), and WPILib -> vxWorks. All of the WPILib routines are short enough to be inlined for free, but the code structure doesn't allow it.

Originally Posted by Ether

2) can each one be used in a critical section

WPILib uses these routines outside of critical regions, so I assume they are either lock-free or have their own independent locks.

Originally Posted by Ether

3) how long does each take to execute, and

4) is there anybody who has authoritative answers to these questions

Testing may be the best way to answer these questions, but I'm also curious about the recommended/official way to handle time. It looks like the FPGA clock is preferred since the other ways of grabbing a timestamp aren't used by WPILib except in Vision. I'll collect some data on our cRIOs tomorrow.