On Saturday, January 17, 2015 at 11:17:55 AM UTC-5, ericgg...@gmail.com wrote: > > I found the examples in 'am335x_pru_package' on GitHub very useful, and > was able to get them working on a 3.8 kernel. > > I have used that. I don't think there is a DMA example that works in there. I have everything working non DMA except the read latency is causing some difficulties in a few situations.
> DDR access will have additional latency but 5.8us sounds high. > Is that for 1 LBBO instruction? > Yes that was for 1 LBBO. It times the LBBO, keeps the maximum and repeats. > How are you timing this (which timer)? > The timer in the PRUSS enhanced capture unit. > What is the CPU doing during this time, if it is running 100% in a tight > loop polling that same memory then CPU/PRU will be in contention, and that > could cause excessive latency. Typically something like the pru interrupt > is needed to let the cpu know that pru is done/ready etc. > I was running various commands to create load. The maximum happened with compiling my code. Reading files was close to the maximum. I was wanting to make sure it will work worst case. The ARM will be reading and writing a file and doing some other work in parallel with the PRU. Without carefully stripping down the system you also don't know what else will decide to run. I am using the interrupt to signal the ARM that it needs to do more work for the PRU. > > > On Thursday, January 15, 2015 at 4:52:40 PM UTC-8, d...@pdp8online.com > wrote: >> >> >> I see up to 5.8 microseconds of latency when the PRU is reading from DDR >> memory. Is it possible to reduce this? I tried changing registers that >> looked promising for giving the PRU priority but they didn't have a >> noticeable effect. This is running on a Beaglebone black using a PRU timer >> to measure the maximum time a LBBO from DDR takes.while the ARM is busy. >> >> >> The examples I found for doing DMA from the PRU were all for older >> kernels and wouldn't work with Linux 3.8.13. Is there an example I missed >> that works with this kernel? >> > -- 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.
