On 8/5/2015 2:41 PM, Lenny wrote: > Thanks Robert, > > that rt linux project seems very interesting, but as you say, it is still > too high-level / multitasking in order to beat the PRU. So one would have > to remove basically all the remaining functionality from rt linux to arrive > at something fast and deterministic at the ns timescale i guess..
Even that's not enough. The "A" in the Cortex-A9 CPU means "Application". The processor core is designed for high speed and *NOT* deterministic operation. There are lots of tradeoffs in application processors made to allow high speeds including pipelining, caching, branch prediction, out-of-order execution, that all have a negative impact on the determinism of code execution times. You will find the PRU, which was intentionally designed for fixed operation times will be _far_ more deterministic than the ARM A9 core even though it's running at only 20% of the speed (due in large part to the intentional lack of the advanced features that _allow_ the A9 core to run at it's GHz clock rate). You can probably come close to the PRU performance determinism on a Cortex-A core if you're willing to dedicate one core of a multi-core part strictly to doing real-time, but the PRU will still probably work better. Especially if you need high-speed I/O, where the single-cycle latency to the direct PRU I/O pins will run _circles_ around anything the ARM core can do trying to talk to the GPIO pins. -- Charles Steinkuehler [email protected] -- 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
