> It may be useful to consider what hostmot2 does, before deciding whether > to do it the same way or differently.
I read the source code. Comment claim "stepgen" position controller use first-order feedforward and proportional error feedback. I expect there will be jitter in position feedback because of period jitter. It is assumed commanded positions will keep within the maximum acceleration/deceleration and velocity. If positions are sent to micro controller it could interpolate between points. Feedback should only be different if micro controller fail to generate pulses. There would however be some delay and I would probably chose to buffer a few positions and then it would work even if a dead line in Linuxcnc is missed although all values must still be sent. > This already produces very good position following despite some jitter > in the PC. Peter does a few additional tricks in his FPGA, like > actually sampling the position a bit before it expects the request for > position feedback to arrive, eliminating jitter of the time the position > feedback is taken. (this involves a PLL in the FPGA that tracks the PC's > servo thread frequency, plus a negative offset so that it can sample the > position early enough) If positions are interpolated between receive times there will some zig-zagging so I would chose micro controller internal clock. Average value is however useful to compensate for clock drift so that micro controller consume step positions at the same rate as Linuxcnc provide them. > (hostmot2 the hal component also offers a mode where its input is > position command, ... Hal block connect position in both direction in *.hal file. Communication between Linuxcnc and card however use speed control with position feedback. Unless there exist an alternative position controller I missed of course. > Jeff Nicklas Karlsson ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
