From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from c2beaomr09.btconnect.com (c2beaomr09.btconnect.com [213.123.26.187]) by ozlabs.org (Postfix) with ESMTP id 8B0D8DE4EE for ; Tue, 19 Aug 2008 22:18:35 +1000 (EST) Message-ID: <48AABB2A.6030607@btconnect.com> Date: Tue, 19 Aug 2008 13:23:06 +0100 From: Richard Whitlock MIME-Version: 1.0 To: Scott Wood Subject: Re: Clock / Timebase / Bus Frequencies Help References: <380-220088118115212377@M2W006.mail2web.com> <20080818155921.GA26475@loki.buserror.net> In-Reply-To: <20080818155921.GA26475@loki.buserror.net> Content-Type: text/plain; charset=us-ascii; format=flowed Cc: "richw@netcomuk.co.uk" , linuxppc-dev@ozlabs.org Reply-To: richw@netcomuk.co.uk List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Scott, Thanks for that - you're right - redboot has the wrong crystal frequency in the cdl for our board. Cheers, Richard. Scott Wood wrote: > On Mon, Aug 18, 2008 at 07:52:12AM -0400, richw@netcomuk.co.uk wrote: > >> We've got an 8347 based board very similar to the A&M asp8347. Core clock >> is 400MHz. Bus clock is 266666666Hz. >> According to the data sheet for the 8347, the decrementer clock runs at a >> quarter of the rate of the bus clock. I have two questions: >> In arch/powerpc/boot/redboot-83xx.c, the timebase clock is passed to >> dt_fixup_cpu_clocks() as bi_busfreq / 16. If I leave it like this, my >> system clock runs approximately 4 times too fast. >> Can anyone point me in the direction of an explanation for the div by 16 >> rather than 4? >> > > It's a bug, which I pointed out here: > http://ozlabs.org/pipermail/linuxppc-dev/2008-June/058704.html > > >> If I change the call to dt_fixup_cpu_clocks so that bi_busfreq/4 is passed >> in, then the clock runs more accurately. However, its still not correct. >> This gives a decrementer frequency of 66666666Hz, but if I hard code the >> value to 66000000Hz, the clock runs accurately. >> Can anyone shed any light on why the value passed in by the boot loader >> (redboot) seems to be inaccurate. >> > > Redboot probably has the wrong crystal frequency hardcoded. > > -Scott > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@ozlabs.org > https://ozlabs.org/mailman/listinfo/linuxppc-dev > > >