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Path: utzoo!watmath!clyde!rutgers!cbmvax!vu-vlsi!elh
From: elh@vu-vlsi.UUCP
Newsgroups: comp.arch
Subject: Re: Using a DMA chip in strange ways
Message-ID: <630@vu-vlsi.UUCP>
Date: Wed, 18-Feb-87 08:26:08 EST
Article-I.D.: vu-vlsi.630
Posted: Wed Feb 18 08:26:08 1987
Date-Received: Fri, 20-Feb-87 06:51:33 EST
References: <4343@columbia.UUCP>
Organization: Villanova Univ. EE Dept.
Lines: 25
Summary: RE: Using DMA chip to copy memory

In article <4343@columbia.UUCP>, dupuy@amsterdam.columbia.edu (Alexander Dupuy) writes:
> ....would
> there be any advantage in having a DMA chip which would simply be used for
> memory to memory copies (from user to kernel space, or from one user space to
> another)?
> 
I believe this is currently a feature on many commercially available
DMA controllers.  In particular, while I was working on the architecture/
partitioning of some of the peripheral chips for the ATT WE32XXX family,
we decided to include this feature in the the DMA member of that family.
This has shown increased performance in memory-to-memory copies in the
operating system (as reported in a paper in the 1986 International
Conference on Computer Design... I forget the exact reference).

This part also has a number of other interesting features including
a *separate* byte wide bus which services commercially available
byte wide peripherals (disk, lan, etc. controllers), byte to word
packing, word buffering and burst mode bus transactions....  The 
peripherals on the byte wide bus lie in the address space of the
DMA peripheral which lies somewhere in the address space of the system
(obviously...).

Dr. Ed Hepler,  Adjunct Prof. Villanova University
                Staff Engineer, GE Astro Space, Valley Forge
                (Formally MTS, Bell Labs, Naperville, Ill.)