[7242] in linux-scsi channel archive
Re: PCI bus speed & recent sym53c8xx driver
daemon@ATHENA.MIT.EDU (Lance Robinson)
Tue Sep 21 22:37:38 1999
Message-ID: <000101bf04a3$d80bde20$060f010a@r16a.com>
Reply-To: "Lance Robinson" <lancer@airways.com>
From: "Lance Robinson" <lancer@airways.com>
To: "Gerard Roudier" <groudier@club-internet.fr>,
"Gregory P. Smith" <greg@electricrain.com>
Cc: <linux-scsi@vger.rutgers.edu>
Date: Tue, 21 Sep 1999 17:51:55 -0700
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Gerard,
See below...
<>< Lance.
On Mon, 20 Sep 1999, Gregory P. Smith wrote:
>> This is what I see:
>...
>> sym53c875-0: on-chip RAM at 0xe2800000
>> sym53c875-0: Delay (GEN=11): 225 msec, 39503 KHz
>> sym53c875-0: Delay (GEN=11): 212 msec, 41926 KHz
>> sym53c875-0: Delay (GEN=11): 213 msec, 41729 KHz
>> sym53c875-0: PCI clock seems too high (41729 KHz).
>Indeed it seems so.
>> [I removed the 'goto abort' in the code so that I could get past here...]
>If the driver is more than 20 % wrong on the estimation of the SCSI clock,
>then it may wrongly enable the SCSI clock doubler of a 875 chip rev >= 2
>using a 80 MHz, and in the worst case, the controller may be damaged. In
>less bad situations, the driver may base it synchronous data settings on a
>wrong SCSI clock value and fail synchronous data transfers.
But the difference between 40000KHz and 41926KHZ is less than 5%. A 10%
difference from 40000 would be 44000, and a 20% would be 48000.
Perhaps you are being too strict on the numbers.
<>< Lance.
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