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Date:      Wed, 23 May 2001 13:58:38 -0700
From:      David Greenman <dg@root.com>
To:        Parag Patel <parag@codegen.com>
Cc:        mike@sentex.net, stable@FreeBSD.ORG, Jonathan Lemon <jlemon@flugsvamp.com>
Subject:   Re: Continuing ahc problems - also cause fxp failure
Message-ID:  <20010523135838.C12931@nexus.root.com>
In-Reply-To: <20010523124522.J68487@prism.flugsvamp.com>; from jlemon@flugsvamp.com on Wed, May 23, 2001 at 12:45:22PM -0500
References:  <jlemon@flugsvamp.com> <4555.990639197@tenor.codegen.com> <20010523124522.J68487@prism.flugsvamp.com>

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>> Some of these problems could be considered bugs in my driver.  :)  It
>> turns out that under heavy loads, the chip may not update its SCB status
>> register soon enough after it accepts a new RU or CU command but has
>> already begun the new command.  If either unit is restarted too soon,
>> double-transmits/receives can occur, out of or into buffers that have
>> already been freed or used for other purposes.

   The resume command is ignored if the CU is already active. The 82557/8/9
also re-checks the suspend flag in the CB to see if it has been updated
before proceeding and will go back to suspended if it has not. If it didn't
do these things then there would be an opportunity for already completed xmit
CB's to be resent. ...So there is no opportunity for double-transmits to
occur unless there are bugs in your driver.

-DG

David Greenman
Co-founder, The FreeBSD Project - http://www.freebsd.org
President, TeraSolutions, Inc. - http://www.terasolutions.com
Pave the road of life with opportunities.

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