In my images, the ARM core is running motion and trajectory planning in a 1 ms (configurable) loop, using the Xenomai real-time patches. If you don't have something like Xenomai or PREEMPT_RT patched into the stock Linux kernel, the 1 mS loops do not execute at the proper time.
The PRUs are used to generate step/direction pulses at (potentially) high speed, running simple code in a short loop (typically 1-10 uS), which is not possible on the ARM. Even with Xenomai, IRQ latency is on the order of 20-60 uS for the ARM, so it just can't run a task loop that fast. The PRUs don't have anything else to do, so they can happily make step/dir pulses with good timings while the ARM core handles the complicated not-so-time-critical stuff like motion planning, and the non-real time stuff like a user interface. On 3/31/2014 10:33 PM, Brad Hopper wrote: > Charles any quick points or a link to something explaining what is the > meaning of real time linux, especially in the context of having PRUs - I > sort of had the sense that, for example in your machine kit image, the real > time bits were being performed by the PRUs, so what is the reason for > Xenomai? You have to run some OS of course, but if you have a dedicated > subsystem that just comes up for air when it needs to inform the OS, why > not just ?plain? linux? And if linux can run real time, why do you need the > PRUs? maybe it's a matter of the scale of latency we're talking about. > > On Monday, March 31, 2014 6:08:27 PM UTC-4, Charles Steinkuehler wrote: >> >> On 3/31/2014 5:54 AM, Eren Basturk wrote: >>> Hi All, >>> >>> I wonder that Is there any real time operating system to use on Beagle >> Bone >>> Black? Could you give me some information about real time linux on >> Beagle >>> Bone? >> >> TI has a list, but it doesn't include everything: >> >> http://www.ti.com/lsds/ti/tools-software/rtos.page >> >> ...conspicuously absent are the various non-commercial solutions. >> >> Is there something in particular you are wanting to run? >> >> -- >> Charles Steinkuehler >> cha...@steinkuehler.net <javascript:> >> > -- Charles Steinkuehler char...@steinkuehler.net -- 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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
