This training material from free-electron explains the cache effects and how to deal with them. Starting at slide 440
http://free-electrons.com/doc/training/linux-kernel/linux-kernel-slides.pdf <http://free-electrons.com/doc/training/linux-kernel/linux-kernel-slides.pdf> Regards, John > On Jan 3, 2016, at 8:58 AM, Thomas Köhler <kingtomm...@googlemail.com> wrote: > > Hello and thank you for the fast help. Here my answers for your comments: > > > Unless you carefully write kernel code to treat your DDR memory buffer > as DMA memory, you are almost certainly encountering caching effects. > > I thought to have this done by getting the memory space from > dma_alloc_coherent(). I will research if there is more needed to disable the > caching but my understanding was that a DMA flagged space will never be > cached because the ARM core can not know if something has changed. > > > I recommend instead of using a buffer in DDR memory, use the PRU data > > memories. > > As to my tests, writing from the PRU to the DDR memory only requires 3 cycles > on the PRU and not more on a few million tries (L3 fast interconnect). > However I do not know how long it takes for this memory to be available at > the ARM... > > I can not do all work in the PRU code because I need to tag the rising edge > with the Linux Kernel time. Therefore I need to find out the most > deterministic way to get the counter value into the Kernel. > > I will do further tests. Maybe there is someone here who experienced the same > road. I think tagging an event with the PRU (5ns) and set it into relation to > Linux Kernel Time without losing to much nanoseconds should be one of the > great PRU benefits. > > Thanks all > > > > -- > For more options, visit http://beagleboard.org/discuss > <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 > <mailto:beagleboard+unsubscr...@googlegroups.com>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- 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.
