Hello, I encounter a caching issue with my application. I will describe what I want to do, how I planned to do it and what goes wrong:
*WHAT:* By using the PRU on my BBB, I want to timestamp a periodic rising edge on one input pin in *a nanosecond scale *and signal it to a Linux Kernel module on the ARM. *HOW:* To receive an interrupt in my kernel module, I bridged the pin with the rising edge to a second one (timer4 interrupt). This interrupt fires a few microseconds after the event happened. To read values from the PRU with best determinism and lowest latency, I allocated some DDR memory with dma_alloc_coherent() in my kernel module and handout the address via debugfs to the PRU. The PRU is in endless loop: wait for rising edge, read out the PRU cycle counter and write the cycle counter to the DDR memory address. *This works like a charm and I got the event's cycle counter snapshot in my kernel module!* The kernel module interrupt is firing a few microseconds after the event and has some jitter I want to avoid. So I decided it would be best to burst the actual cycle counter to a second ram address for a ten thousand times by the PRU so when the Kernel module reads this ddr location, It knows the difference from the event's cycle counter and the cycle counter now. *This does not work!* *WRONG:* Initially everything appered to be working. I was reading out for example: event cycles: 1000 now cycles: 4300 great! But to test the "now cycles" counter, I added to the kernel module to read it thousand times in a loop. Guess what?* It is thousand times the same.* I tried a few options. For example to write and read two alternating memaddresses for this "now counter" by kernel and pru but nothing gives the results I expected. It seems like anyone caches the results..... Any help? So many thanks... I hope the problem can be understood. Tom -- 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.
