On 11/20/2018 6:08 PM, Gerhard Hoffmann wrote: > > Am 20.11.18 um 23:15 schrieb Mark A. Yoder: >> >> Using the PRU interface is faster. I think my students measured >> it as being a couple times faster. Using the PRU interface you can >> toggle a pin every 5ns. >> >> > Yes, R30/R31 is about 3 times as fast and more predictable. Going > through the OCP interface > > has to wait sometimes if there is already CPU or DMA activity.
PRU writes to the direct I/O are 8 times faster than writing to a GPIO pin via the OCP (40 ns for the GPIO vs. 5 ns for direct I/O). Note that while the write competes on the PRU side within 40 ns, it takes about another 100 nS until the actual GPIO pin value is updated (this is the time needed for the write transaction to flow through the interconnect fabric and actually update the GPIO register). Reads, however are much worse, since they are not posted by the interconnect fabric and stall the PRU until the read value is returned. Reading from a GPIO pin via the OCP port takes apx. 165 ns vs. 5 ns for a direct I/O read. I did some tests and measurements of this when I was writing the PRU code for Machinekit, and documented the details in some comments: https://github.com/machinekit/machinekit/blob/master/src/hal/drivers/hal_pru_generic/pru_generic.p#L137-L165 -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/3b658492-eea7-43b5-4c93-2d6f9dd9fdb8%40steinkuehler.net. For more options, visit https://groups.google.com/d/optout.
