On Mon, Aug 05, 2013 at 09:25:18AM +0200, Michael Schnell wrote: > > You can't. And you can't, even if you try to run bare-metal software > > on a dedicated core. I can't imagine how for example the cache > > influences between the cores could be determined. > > This would render all efforts for hard realtime embedded Linux > applications useless. You always need to calculate the max latency. You can't calculate the max latency with today's complex processor hardware any more. It's all a matter of system failure probabilities. > Using a dedicated Core will certainly reduce the max latency, but of > course it will not do away with the necessary calculations that take > into account what the other CPUs might do (regarding second level > Cache, cache synchronization, bus scheduling, etc.) I don't think it is possible to get an analytic result for the max latency introduced by other CPUs. What we do today is to run preempt-rt systems, measure them under realistic and extreme load and look at the max latencies. If you design your system in a way that it runs at factor X above this max latency, it should be fine. The advantage of preempt-rt is that you have only one software environment for rt and non-rt. Nevertheless, there always have been settings where you could get rid of all realtime complexity by spending a 1-Euro microcontroller to the BOM. > IMHO, a good compromise is the TI 335x chip that has a single 1 GHz > Cortex A8 and two 300 MHz Cortex A3 cores for a very reasonable price > and and "embedded" specs for temperature range and future chip > availability. AM335x has PRU subprocessors (not ARM architecture). Yes, that can be a solution. Freescale's Vybrid has Cortex-M3 cores. > Right now, I am just investigating viable ways to do things, before > doing a pre-decision for any hardware and starting do dive into that. What kind of application is that? rsc -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
