I would be stunned if the GPIOs don't have synchronizer flip-flops as they are sampling a signal asynchronous to the 200MHz clock. That would account for 2 clocks. You probably need one extra to clock data into R31. And then one clock to read R31.
50MHz is a pretty smoking speed for SPI--you normally need to start thinking about series termination and some basic signal integrity. You normally need the clock to capture to flop directly if you want things to work. I suspect you probably need to use the 16-bit Parallel Capture Mode while feeding your clock out back as clock in. You'll still probably be 4 clocks behind when the data hits R31, but the data will get *captured* by the PRU<n>_CLOCKIN edge properly so the delay will now be deterministic if you are generating the 50MHz clock yourself. On Thursday, February 25, 2021 at 12:15:18 PM UTC-8 rpau...@gmail.com wrote: > With a sample size of one, r31 appears to be 4 instructions behind the > state of the pin. > > On Thursday, February 25, 2021 at 12:26:16 PM UTC-5 Paul Beam wrote: > >> I am, unfortunately, bit-banging SPI with the PRU, and I seem to be >> running into a speed limit < 50 MHz I desire. I can certainly create a >> clock that fast, but reading data seems to be delayed. I can see on the >> logic analyzer a "0" clearly being read as a '1" so there is either a delay >> in my clock output or a delay in my input or both. I would like to think >> that r30 and r31 are tied directly to the outside world, but now I am >> thinking there is something in between that is either clocked or just has >> significant output delays. Anyone else encountered this? > > -- 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/f88c700e-69c2-4ac4-bc64-d44a1715460dn%40googlegroups.com.
