Date: Sun, 7 May 2000 12:45:25 -0700 (PDT) From: Matthew Jacob <mjacob@feral.com> To: =?ISO-8859-1?Q?G=E9rard_Roudier?= <groudier@club-internet.fr> Cc: alpha@FreeBSD.ORG Subject: Re: AlphaServer 4100 Support being integrated Message-ID: <Pine.BSF.4.05.10005071242380.21956-100000@semuta.feral.com> In-Reply-To: <Pine.LNX.4.10.10005072036220.885-100000@linux.local>
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> > On Sun, 7 May 2000, Matthew Jacob wrote: > > > Hmm. It's a normal PCI bus. If DELAY is wrong on alpha's, this may explain > > some of the funnies I've seen elsewhere. Thanks for spotting this. > > I looked into the source and it seems obviously wrong to me. It is based > on a loop that is hardcoded as lasting 3 cycles. This is probably correct > for some CPU types but certainly not for all. For the CPU of the 4100 and > given the actual memory alignment of the loop code, it could well be that > the loop cost is actually 2 cycles instead of the hardcoded 3 cycles (just > a guessing based on the below biased value displayed by `sym'). Yeah, I've been looking at it. I'm playing around with an assembler replacement as we speak. > The `sym' driver may estimate the SCSI clock for chips that should use a > 80 MHz clock or use a 40 Mhz clock and may have a clock multiplier. Given > the bias due to DELAY() error the driver will estimated SCSI clock > frequency as follows: > > If actually 40 Mhz, result will be 26,6 Mhz. > Driver will assume 40Hz --> NO HARM. > > If actually 80 Mhz, result will be 53,3 Mhz. > Driver will assule 50Hz --> BAD SPOT. > A 860 or a 875 may not properly work in that situation... > But if the booting software properly set SCNTL3 and clock multiplier > if any, the driver may just trust IO registers values for its guessing > of the SCSI clock frequency --> NO HARM. All good points. You have to have a good clock, there's no question about it. -matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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