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Date:      Tue, 13 Jun 2000 19:33:03 +0200 (CEST)
From:      =?ISO-8859-1?Q?G=E9rard_Roudier?= <groudier@club-internet.fr>
To:        "Kenneth D. Merry" <ken@kdm.org>
Cc:        Todd Cohen <cohentl@clarkson.edu>, freebsd-stable@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG
Subject:   Re: Problem with newer sym driver on a Tekram DC-390U2W controller
Message-ID:  <Pine.LNX.4.10.10006131915100.461-100000@linux.local>
In-Reply-To: <20000613103825.A24786@panzer.kdm.org>

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On Tue, 13 Jun 2000, Kenneth D. Merry wrote:

> On Tue, Jun 13, 2000 at 12:16:59 -0400, Todd Cohen wrote:
> > Different but related question, are the DC-315U cards supported?
> 
> If you use Tekram's driver, yes.
> 
> Those cards, as well as their DC-395 series cards are based on Tekram's own
> S1040 chip.
> 
> >From the driver, though, it appears that the card doesn't have a SCSI phase
> engine, so there will be multiple interrupts per transaction.

And it appears that some non negligible amount of IOs through the PCI BUS
is to be performed for each interrupt. When the BUS is busy, this may
result in the CPU being stalled uselessly for micro-seconds (equivalent to
thousands of instructions lost given modern CPUs).

Under an O/S or a system that is either doing one thing at time or nothing
most of the time, this probably does not make significant difference. 
But under a UNIX O/S, this probably is a significant penalty compared 
to SYMBIOS chips (given an appropriate software driver that takes
advantage of SYMBIOS chips capabilities).

Price difference between Tekram 3X5 and SCSI mode equivalent but PCI far
superior Tekram 390-X controllers seems low-enough for me to claim that
purchasing a 390-X is a far better buy. If we take into account the price
of SCSI devices, then bying a 3X5 boards seems just stupid to me.

> You would probably be beter off getting one of their Symbios/LSI based
> boards.

Indeed.

  Gerard.



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