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Date:      Wed, 07 Jun 2000 22:48:17 -0700
From:      W Gerald Hicks <jhix@mindspring.com>
To:        hackers@FreeBSD.ORG
Subject:   Re: if_dc in v4.0 - Forcing store and forward?
Message-ID:  <393F33A1.2AE75730@mindspring.com>
References:  <20000608000153.6AC291CE1@overcee.netplex.com.au>

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Peter Wemm wrote:

> I suspect a generic chipset fault, or some design quirk that we are not
> working around.  Note that the windoze drivers for these devices put them
> permanently in store-and-forward mode.  if_de has the exact same problem on
> all of the systems above.
> 

I'll second this.  It doesn't appear to be a FreeBSD specific issue
either, as I've experienced it with VxWorks and pSOS as well.  ISTR that
the Linux driver works in store and forward mode (or did last year).

I'm pretty sure there exists a workaround, based on an experience I had
with VxWorks.  The stock VxWorks driver was practically unusable;  when
we obtained a custom driver from Artesyn the problem disappeared and we
were able to achieve reasonable 100 Mbit performance with zero transmit
underruns.  By contrast, I couldn't get better than 12 Mbit throughput
from Wind River's driver and we would experience a tx underrun at least
once every minute.

Store and forward mode introduces a horrible performance hit...  Artesyn
wouldn't show us the source to their workaround  :-(

--
Jerry Hicks
jhix@mindspring.com


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