[vortex] Re: MTU discovery

[Donald Becker]

On Mon, 10 Jun 2002, Matti Aarnio wrote:

> Date: Mon, 10 Jun 2002 11:05:13 +0300
> From: Matti Aarnio <matti.aarnio@zmailer.org>
> To: Robert PipCA <robertpipca@yahoo.com>
> Cc: vortex@scyld.com, linux-kernel@vger.kernel.org
> Subject: [vortex] Re: MTU discovery
>
> On Mon, Jun 10, 2002 at 12:45:07AM -0700, Robert PipCA wrote:
> >   Hi,
> >   I'm working on a project that require knowing the max MTU size
> > supported by the 3Com PCI 3c905C (Boomerang).
> > The datasheet provided by 3Com does not mention it, and I already
> > did the usual google search, but didn't find it neither.
> > Does anyone knows a "generic way" of knowing this (or chip-specific)?
..
>   Some devices do, however, support reception (and transmit) of what
>   is called "jumbograms".  With boomerang you can set a register
>   to contain the limit value.

A 16 bit register.. 64KB packets.  There are various issues with using
large packet sizes.  There is no driver that has been verified with
jumbo frames.  I have been throwing driver versions at Rishi Srivatsavai
<rishis at CLEMSON.EDU> trying to sort out the issues.  You might notice
the changes in 0.99W, although they don't handle the FIFO limit issues.

>  Alternatively with boomerang, and
>   its predecessors, you can set a bit to accept extra-large frames.
>
>   I recall the ultimate limit is in order of 4kB.

More precisely, FDDI frame size minus the FDDI-specific bits, about
4.5KB.

-- 
Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
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