From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 6 Sep 2001 11:06:07 +1000 From: David Gibson To: linuxppc-embedded@lists.linuxppc.org Subject: Re: 4xx - a question and a patch Message-ID: <20010906110607.C20279@zax> References: <20010830175217.H858@zax> <3B95307D.1BE64A98@mvista.com> <20010905110451.A599@zax> <3B95A796.248A0E99@mvista.com> <20010905144125.H6636@zax> <3B9645EB.DC7F3A6C@mvista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <3B9645EB.DC7F3A6C@mvista.com> Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: On Wed, Sep 05, 2001 at 11:34:03AM -0400, Dan Malek wrote: > > David Gibson wrote: > > > But when it hits zero we'll also get another timer interrupt and will > > shortly be updating it with a corrected value. Why does it matter > > that the value is reloaded? > > I don't understand the reason for this discussion. Is something > not working correctly? If so, make it work better and send me a > patch. Well, there's nothing actually broken, but allowing the set_dec() in timer_interrupt() to affect the PIT should keep the timer interrupts from drifting too far from the time base, and hence slightly reduce the jitter in jiffies. But, no, I don't actually have any timings or data to confirm that that is the case. I've been running this way in my kernel for a month or so, so it certainly doesn't break anything badly. I'm trying to find out if my understanding of the situation is actually correct. And the patch: diff -urN ../linuxppc_2_4_devel/include/asm-ppc/time.h linux-bungo/include/asm-ppc/time.h --- ../linuxppc_2_4_devel/include/asm-ppc/time.h Wed Aug 29 10:41:56 2001 +++ linux-bungo/include/asm-ppc/time.h Thu Sep 6 11:01:04 2001 @@ -46,7 +46,7 @@ static __inline__ void set_dec(unsigned int val) { #if defined(CONFIG_4xx) - return; /* Have to let it auto-reload */ + mtspr(SPRN_PIT, val); #elif defined(CONFIG_8xx_CPU6) set_dec_cpu6(val); #else -- David Gibson | For every complex problem there is a david@gibson.dropbear.id.au | solution which is simple, neat and | wrong. -- H.L. Mencken http://www.ozlabs.org/people/dgibson ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/