Sep 14, 2019, 20:04 by [email protected]: > Doing a little testing on my hardware I noticed there is an issue with > encoder indexes being missed while trying to count them. It's difficult in > hal to see the index pin change state on an encoder with reasonable > resolution because the change in state is very short. So I added the function > in my GUI to count up the encoder index pulses because it's obviously more > visible when a number increments up vs trying to catch a small blip in > halshow or halcmd. I noticed the index pulses are missed spinning the encoder > at anything other than a very slow speed. I'm not really sure what > communication method mksocfpga uses between the fpga and the cpu but I > figured I'd try running a few non-fp components in a 0.2ms base thread to see > if it helped. Didn't really seem to help at all > > I first tried this by routing the hm2<board>index-input hal pin into the > updown component and sending the counts to a hal label in my gui. My first > thought is that the state change is too short for the servo-thread to catch > at 1ms, so I added the "edge" component to extend the length of the > index-input on it's output but that didn't really help. The output of edge > obviously only get's extended if it catches the input state change which it > does no better than updown. > > The conclusion I'm drawing is that the RT behavior of the CPU or the > communication between the FPGA and CPU cores is too slow for whatever reason, > that or there's some issue with the encoder module in mksocfpga's hm2. I'm > using 3 channels of a quad differential receiver chip for each encoder input. > There is no difference between the index channel and A-B channels hardware > wise, and this is the same on 6 identical instances of encoder inputs. The > only difference is that hm2 counts the A-B channels in the FPGA while the > index is not. I haven't seen any indication of missed counts on the A-B > channels counting 4000 edges in quadrature. I've messed with the hm2 encoder > sample-frequency too which also did not help. The only thing that helped > somewhat is running a 0.5ms servo-thread but it still missed quite a few > index's, and this is with me spinning the encoder by hand. > > I use this same model of encoder on a LinuxCNC machine with a Mesa 7i96 and > again on a 7i76e and I've never really seen an index missed on those spindle > motors at ~3000rpms. If this isn't an issue with the hm2 encoder module > itself I'd expect to see the same issue with a normal GPIO input missing > short/fast pulses but I would think that someone else would have noticed that > issue by now? > > Thoughts? > Stupid question, but how exactly are you counting the Z pulses in your GUI? Are taking into account the non-RT nature of the GUI?
I don't remember how exactly is the communication done in HostMot2, but I remember that you have to "compute" the index signal from A/B registers if you were to catch the sampling message (request and response from FPGA layer) outside the index occurrence. Cern. -- website: http://www.machinekit.io blog: http://blog.machinekit.io github: https://github.com/machinekit --- You received this message because you are subscribed to the Google Groups "Machinekit" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/machinekit/Lol_BfY--3-1%40tuta.io.
