How does DMA work?

[jlwalter@primenet.com (Joe Walters)]

I received an e-mail praising my post of the RamFASt manual from Jim
Fraser of Oz fame and the following question. Since I don't have a
TWGS I could not answer.

> Here is a fairly dumb question, which I couldn't resolve from the
> manual - with an AE TWGS (with gal 2B) and the AE GS-Ram Plus Rev
> D, what is it that enables me to know if DMA is taking place?

I think that this is a two part question. The first part answers Jim's
question and the second answers my expansion on this subject. All feel
free to jump in with your answers, etc.

After reflection I find that I have a number of questions on this
subject:

1. How does turning on DMA change the way my Apple and the associated
   card work? (I know that the disk read somehow goes directly to the
   destination memory. How is this effected? Said info needs to be
   if a FAQ of some sort. Or I need to be pointed to an existing FAQ.)

2. How does turning off DMA change the way my Apple and the associated
   card work? (The oppoosite of question #1.)

3. And the question in the post, "What enables me to know that DMA is
   taking place?" (I suspect nothing external is available. Only the
   DIP/Soft switches for your SCSI card, "give it all away.)

> DMA is turned on and I don't have many crashes :-)

I guess you need to define too many crashes ;-)

BUGGIE ALERT!! I found that my crashes have pretty much disappeared
since I got my Buggie power supply. Hate to keep harping on this,
however, a number of posts back me up on this matter. Before I got my
Buggie power supply I was *seriously* considering going to the dark
side. Not now; especially since SIS is available AND *I suspect*
TCP/IP for SIS in the future. Send in your $25 folks! SIS looks like a
real winner!

Kind Regards,


--
	Joe Walters:  bird@mcs.net
	To know and not to do is to not yet know