Peter C. Wallace wrote: > > > Our older configs did this but LinuxCNC seems to want to be in charge of the > timimg... > Well, it would not need to be the driver that receives the interrupt. The interrupt handler could be rtapi, the only real difference is that rtapi would not be calling for a regularly scheduled interrupt using the CPU's interval timer facility, it would be some other interrupt provided by a device. (It would still be regularly scheduled, but rtapi would not be selecting the interval, it would be coming from the master PPMC device, in this case.) Actually, there are a couple ways of doing it. There is a parallel port line I have dedicated to the interrupt/latch function. Either the host system or the PPMC device can control it, and when pulsed, all the PPMC devices latch all information that needs to be sampled simultaneously. Mostly, that is the encoder counts and the encoder timestamps. On the analog servo system (PPMC board set) this also updates the velocity DAC values. So, if the PRU could receive a timer pulse and send out this pulse, that would be fine. The current problem is if the servo thread has a large latency at the beginning of invoking the thread, the encoder sampling is delayed. You can look at the par port line I mention above and see the jitter. Normally, it is pretty small, a few us, but I think there are larger variations every once in a while.
One advantage in using the PRU to generate the sample pulse is that any servo thread rate could be selected, I only have 4 rates possible from my boards. Anyway, if major work is going to be done in rtapi (I guess some part of this has already been done) we ought to see if there's a way to incorporate one of these schemes. Jon ------------------------------------------------------------------------------ See everything from the browser to the database with AppDynamics Get end-to-end visibility with application monitoring from AppDynamics Isolate bottlenecks and diagnose root cause in seconds. Start your free trial of AppDynamics Pro today! http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
