Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!emory!ogicse!jmeissen
From: jmeissen@ogicse.ogi.edu (John Meissen)
Newsgroups: comp.sys.amiga.hardware
Subject: Re:   GVP Trade-in
Message-ID: <11853@ogicse.ogi.edu>
Date: 31 Aug 90 21:15:23 GMT
References: <589@oregon.oacis.org> <38CP09P@dri.com> <02048.002057@thiger.UUCP> <552@DIALix.UUCP> <02123.132132@thiger.UUCP>
Organization: Oregon Graduate Institute (formerly OGC), Beaverton, OR
Lines: 40

In article <02123.132132@thiger.UUCP> skraw@thiger.UUCP (Stephan von Krawczynski) writes:
>>DMA is an advantage because the CPU can be doing other (real
>>processing) things.
>
>the problem is: if dma-transfer from controller to fast-ram takes place,
>is the processor able to access this fast-ram at the same time?
>(may be implemented via splitting the totally available access-cycles)
>for if it is not, your processor will do ABSOLUTELY nothing, because
>it's cut off the bus (with exception of real weird programs that have
>the luck to be inside the instruction cache when dma starts and
>need no data from "outside"-world).

The other side of the coin is that when doing DMA, it doesn't matter
if the processor is cut off from the bus and incapable of doing anything
else. The simple fact of the matter is, if you DIDN'T have the DMA, then
the processor would be tied up doing the transfer and STILL wouldn't
be able to do anything else. And in a comparison of DMA vs CPU transfer
of data, the DMA is much faster; thus the CPU will be prevented from
doing usefule work for a much shorter period of time.

Either way you win with DMA.

>>You can also connect
>>more than one drive without "choking" on the bus, especially during
>>overlapping seeks and transfers.
>
>what do you want to say here, i don't understand this.

If you have data transfer operations going on multiple drives
simultaneously, a properly designed DMA controller will be able to
interleave the operations, effectively allowing them to run at the
same time. A processor-based scheme can only handle one operation
at a time.


-- 
John Meissen .............................. Oregon Advanced Computing Institute
jmeissen@oacis.org        (Internet) | "That's the remarkable thing about life;
..!sequent!oacis!jmeissen (UUCP)     |  things are never so bad that they can't
jmeissen                  (BIX)      |  get worse." - Calvin & Hobbes