Windows Media Player makes NI-Motion calls faster (revisited)

[chvogt · Accepted solution]

While trying to implement my own throttle, I ran a timing test to check how well my throttle was working. I was surprised to find that I was only getting 100 calls/sec. When I looked into this further I found that the resolution of the timer that I was using was only 10 ms. I am using the 'timeGetTime' function in 'winmm.dll' since it provides a higher resolution than the standard timer used in VB.

I found that the resolution of the timer can be controlled using the 'timeBeginPeriod' & 'timeEndPeriod' functions in 'winmm.dll'. I added a check box to my WMPTest program to allow the 1 ms resolution to be selected and left the built-in NI-Motion throttle enabled. I found that this was all that was needed to make the NI-Motion calls work faster. Specifically, I added a 'timeBeginPeriod(1)' call before the timing loop and a 'timeEndPeriod(1)' call after the timing loop is complete. The new WMPTest program is attached.

Here are the results:

                    

I would need to use the timeBeginPeriod & timeEndPeriod functions to make my own throttle work, but since they also affect the NI-Motion throttle I'll probably just leave the NI-Motion throttle enabled and let NI-Motion do it's own thing. MSDN says that setting a higher resolution can 'reduce overall system performance, because the thread scheduler switches tasks more often' and can 'prevent the CPU power management system from entering power-saving modes'. Neither of these should be an issue for me because the computer is dedicated to running the tests and all power saving is disabled anyway.