Subject: Re: LANCE (Am7990) DMA
To: Jason Thorpe <>
From: Matt Thomas <>
List: tech-net
Date: 10/05/1998 21:41:21
At 09:14 PM 10/5/98 , Jason Thorpe wrote:
>On Mon, 05 Oct 1998 21:27:53 -0700 
> Matt Thomas <> wrote:
> > Am I reading the lance code correctly in that none
> > of the le drivers actually do DMA directly to/from 
> > mbufs  but actually have other buffers they DMA with 
> > and then copy to/from mbufs from those buffers?
>That's correct... that's the way the driver is currently structured.
>Note, that's safest for e.g. ISA-based LANCE boards, as well as any boards
>where it can only DMA to on-board memory.

So on the VAX 4000/60 where it has a scatter/gather map which can
allow it to address all of memory (or on the VS2000 which only
has 14MB of memory), the current driver forces an extra data copy 
where none is needed.  That's really painful on VAXes which have
already very slow memory bandwidth.  Maybe that means I really
can't the MI le driver.  Ugh.
Matt Thomas               Internet:
3am Software Foundry      WWW URL:
Sunnyvale, CA             Disclaimer: I avow all knowledge of this message