From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?iso-8859-1?Q?Lambrecht_J=FCrgen?= Subject: Re: AMP on an SMP system Date: Mon, 5 Aug 2013 12:00:02 +0200 Message-ID: <51FF77A2.7030904@televic.com> References: <51FB6EE1.3090708@lumino.de> <51FEC76C.70908@televic.com> Mime-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <51FEC76C.70908@televic.com> Content-Language: en-US Sender: linux-embedded-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="iso-8859-1" To: Michael Schnell Cc: "linux-embedded@vger.kernel.org" On 08/04/2013 11:28 PM, Lambrecht J=FCrgen wrote: > On 08/02/2013 10:33 AM, Michael Schnell wrote: > [snip] >> - how to assign certain interrupts to that core and have ISRs ru= n >> there only dedicatedly interrupting the "main loop" and not ever bei= ng >> blocked by any Linux activity ? >> here I found this: >> https://access.redhat.com/site/solutions/15482 >> In fact of course the hardware defines if/how a certain Interrupt ca= n be >> assigned to a certain CPU. How is this usually done when using ARM >> Cortex A9+ cores ?. > The ARM A9 datasheet will say what registers to write to assign IRQs = to > CPU1, and make Linux not to use those IRQs. > Then the max. latency is determined by the clock speed and CPU cycles > the bare metal program needs to react (should be in datasheet). I asked a Freescale FAE and the cortex A9 is AMP capable (I also needed= =20 to know this for my project): "Actually, you can check on ARM community web site, where you will see = that the CortexA9/GIC infrastructure enables AMP implementation. http://forums.arm.com/index.php?/topic/15656-cortex-a9-amp/ The Global Interrupt Controller gives you the possibility to assign spe= cific IT to specific cores. But a CortexA9 is not very RT oriented (for= that ARM has created the Cortex R Family, with improved RT execution t= ime)." > > About the non-determinism of modern hardware: if a chip is AMP capabl= e > the heating up of 1 core should not influence the other core. I belie= ve > heat spreads vertically (to the heatsink) and not so much horizontall= y. > So an RTOS should run with a stable frequency. (anyhow, Linux should = not > touch the other CPU, or need to touch it). That Freescale FAE warns about the voltage scaling: "you have only one=20 power line to supply all the cores, so all processor would be impacted.= =20 There is no way to change that." So indeed a problem with modern hardware.. Kind regards, J=FCrgen-- To unsubscribe from this list: send the line "unsubscribe linux-embedde= d" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html