Quote:
Originally Posted by JamesTerm
In the WPI Lib PID code in PIDController.cpp (as of version 3487) opens a Notifier object with a default parameter of 50ms. It does like you describe forces the loop to a certain timing, and the reason for this is that this design does not wish to calculate uneven time slices within the PID algorithm. The result is good results from a functionality standpoint, but will have the same issue of context switching especially if one wishes to use a lower period. In c++ the programmer does not have to go in this direction, they can write their own PID http://www.termstech.com/files/Archi...Controller.zip and avoid context switching all together. I had proposed this solution for the WPI library but there was not enough expressed interest in going in this direction. Really when you think of it... a machine can only execute one instruction at a time... when you have tasks/threads... the context switch overhead can really eat up cpu processing, and it doesn't have to be this way. I have spent several years on this issue documented here http://www.termstech.com/articles/PID_Kalman.html |
Our homebrew PID normalizes for time, so the calculation itself does not need to be inside a timed loop. We place it in a timed loop so that we can attempt to match the speed controller update rate for the best 'idealized' performance. I'm not sure how you'd go about this without a timed loop.