From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtpauth.hypersurf.com (smtpauth.hypersurf.com [209.237.0.8]) by ozlabs.org (Postfix) with ESMTP id AEE9CDDE00 for ; Fri, 14 Nov 2008 09:30:50 +1100 (EST) Received: from [192.168.1.37] (66-81-71-173.bayarea.dialup.o1.com [66.81.71.173]) (authenticated bits=0) by smtpauth.hypersurf.com (8.14.2/8.14.2) with ESMTP id mADMTNC5043804 for ; Thu, 13 Nov 2008 14:30:41 -0800 (PST) Message-ID: <491CAA32.20307@hypersurf.com> Date: Thu, 13 Nov 2008 14:29:06 -0800 From: Kevin Diggs MIME-Version: 1.0 To: linuxppc-dev@ozlabs.org Subject: Re: pmac_zilog debugging ... References: <4914B549.9010805@hypersurf.com> <1226096603.13603.74.camel@pasglop> <491C11B2.1060909@hypersurf.com> <1226612654.7178.84.camel@pasglop> In-Reply-To: <1226612654.7178.84.camel@pasglop> Content-Type: text/plain; charset=ISO-8859-1; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Benjamin Herrenschmidt wrote: > On Thu, 2008-11-13 at 03:38 -0800, Kevin Diggs wrote: > > >>12,206 PowerMac Zilog interrupts >> >>Interrupt load is higher without the DMA support. >> >>Is it possible that this hardware was not meant to be used without the >>DMA (i.e. it does not work quite right?)? > > > Well, the HW Rx buffer is only 3 bytes so if you have high interrupt > latencies you are more likely to loose data... > These are not real 8530s any more, right? How certain are we of this? Is it possible that there is a larger buffer when used with the DMA capability ... somehow? > Now, as I said, have you looked at flow control ? It's a likely cause of > problems and it's possible that pmac_zilog doesn't do it the way > macserial did... > I tried to put some debug statements where the flow lines are managed. I could have goofed it up. They never produce any output. The latest attempt used nortscts which should have disabled flow control. That coupled with the fact that a 250 MHz 750GX is talking to a 486dx4 at 1200 - 9600 baud I would have thought would reduce the chance the PowerMac would fall behind? > Regarding DMA, it's possible to implement, though there were interesting > issues with the way it was done in macserial, it should be done > differently in pmac_zilog. > > I think the only approach that really works properly (though it's fugly) > is what Apple does in OSX I think, which is to have a DMA descriptor per > input byte (no need for a huge DMA buffer anyway). > You would need to explain to me the advantage of doing DMA in this case??? > Cheers, > Ben. > >