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From: gemini@geminix.in-berlin.de (Uwe Doering)
Subject: Re: FreeBSD: ASUS SP3G and writeback caches
Keywords: FreeBSD
References: <344vevINN2t7j@rs1.rrz.Uni-Koeln.DE>
Organization: Private UNIX Site
Date: Sat, 3 Sep 1994 11:08:57 GMT
Message-ID: <M47RBQRJ@geminix.in-berlin.de>
Lines: 34
se@fileserv1.MI.Uni-Koeln.DE (Stefan Esser) writes:
>Maybe something got broken in going from FreeBSD-1.1 to 1.1.5 ?
>
>There have been some reports on problems with the ASUS SP3G
>and the PCI SCSI driver, if the secondary cache has been
>configured for writeback operation. The PCI driver makes
>the NCR do lots of bus master operations to a data area that
>is written to by the CPU as well (command queues), and is the
>only FreeBSD driver so far, that depends on cache coherency
>for PCI to memory operations.
I've seen this problem on an ASUS SP3G with an AHA1542CF controller as
well (FreeBSD-1.1.5, i486DX2/66 CPU). So I don't think that this is a
PCI related problem. It's more likely that you need to select `write-
through' because the current ASUS SP3G doesn't have a Dirty Tag SRAM
and therefore the secondary cache can't work in `write-back' mode.
Yes, I know that other MBs work in a pseudo-`write-back' mode even
without a Dirty Tag SRAM (with reduced performance, of course) but
apparently the ASUS SP3G doesn't support this mode.
So, before concluding that the ASUS SP3G isn't capable of secondary
cache `write-back' operations I would rather wait until there are ASUS
SP3G MBs available that are equiped with a Dirty Tag SRAM and then
check again. Rumor has it that these MBs are already available in
Taiwan at this time so it should be just a matter of weeks until they
show up on the US and european market. It's a shame, however, that
they came out w/o a Dirty Tag SRAM in the first place.
Uwe
--
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