On Sunday, September 11, 2016 at 2:45:32 PM UTC-4, Charles Steinkuehler wrote: > > On 9/11/2016 9:14 AM, beezerlm wrote: > > I think my project would be simple enough to run through the PRU. My > current > > PLC loop I am running in the motion control software is just a few > ifElse > > statements that monitor position and change direction. Does the PRU > have access > > to the eQEP without adding latency? > > No and yes. :) > > No: Everything adds latency, even reading the PRU's direct inputs > (although that only takes one clock cycle or 5 nS). > > Yes: Reading the eQEP from the PRU will only take a few hundred nS > (during which time the PRU will be stalled), and the timing jitter > will be fairly low. Unless you have particularly critical timing > issues you didn't mention, the PRU can easily perform a few reads of > the eQEP module while running whatever other control routines you need. > > > It's been a long time since I worked with a linux real time kernel and > HAL. I > > did a similar project a long time ago using linuxCNC to control a Moog > hydraulic > > servo-valve on an old Heald ID grinding machine. That was pretty cool > to see > > linux handle a Hydraulic cylinder on a PID loop. Here is a quick vid of > it: > > > > https://www.youtube.com/watch?v=NMkNCSUJBvs > > > > The machinekit distro looks very similar but more streamlined and with > better > > hardware than what I had. I will have to dig into that a little more. > > If you're already somewhat familiar with HAL, this could be a good way > to go. As I mentioned there are already eQEP and I/O drivers > available, as well as building blocks like PID controllers, > comparators, and even a classic ladder-logic control if you want to > just port your PLC application. You can test things easily with the > pre-built Machinekit uSD card image...just pop out the uSD if you > decide you don't like using Machinekit: > > > http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#BBW.2FBBB_.28All_Revs.29_Machinekit > > > -- > Charles Steinkuehler > [email protected] <javascript:> >
Well as far as I can tell, a few hundred nanoseconds would be great! I just ordered a BBB so I can familiarize myself with it a bit. I guess I wouldn't consider myself proficient with the Linux HAL seeing as I have only used it one time to set up a machine. Wouldn't latency and jitter be lower going direct through the PRU instead of utilizing the HAL assuming the PRU was capable of handling my logic loop? -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" 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/beagleboard/72e028a5-cf96-4687-9ab7-ecedfdde95f0%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
