Re: How to test if your memory card is DMA compatible?

["Henry" <apl2research(.a.t.)comcast.net>]

Hello AMart.

I believe the MicroDrive/Turbo's firmware is limited to only using DMA for 
the first 4 Megs of RAM.  So if you have over 4 Megs of RAM in the expansion 
Slot you shouldn't encounter an issue.  The Apple II High Speed SCSI I think 
does have an issue where it will try to DMA in to all available expansion 
RAM and cause data corruption issues.  The RAMFast SCSI I think allows DMA 
in to all RAM using some RDY interrupt signal (Anyone confirm this?).  Don't 
hold me to this as fact as I think I read that somewhere but have yet to 
personally document it.  I think I also read somewhere that if you had a 
TransWarp GS installed in the same machine that AE didn't totally follow 
Apple's guide lines for accounting for this possibility (16bit caching issue 
vs. 8bit caching like the ZIP GSX?) and those two cards together would cause 
data corruption issues.  The ZIP GSX though doesn't have that issue.

Good question though.  I know I had asked something similar a few months 
back and never really received a reply.  From what I can tell it mainly 
depends on the card trying to do DMA access rather then the memory card 
itself, but I could be wrong.  Anyone?  Also AE made some weird 'DMA Module 
for the GS-RAM Plus card that allegedly prevents DMA issues, but I've yet to 
find anyone that's even seen the card no less own one.  I don't even think 
Tony owns one.  So it may have just been a marketing ploy.  Personally I 
can't see how such a module would even work.

I need to get my IIgs Technical Reference back from my buddy, but I kind of 
remember reading that only 4 Megs was supported by Apple since the address 
decoding logic on the IIgs Motherboard was limited, no fault of the CPU. 
Talking about the IIgs Technical Reference... Anyone have a .PDF of the 
book?  I ordered it from Syndicomm so I own it, but shipping it back and 
forth is killing me in postage as it weighs a ton.  I asked Eric Sheppard, 
but he said he wasn't able to release it.  Just email me directly.  I'd 
really appreciate it!


-- 
Henry S. Courbis
www.GSE-Reactive.com
Legacy Hardware and Support - Come take a look at what we have to offer!


<AMart79196@gmail.com> wrote in message 
1180885823.336051.225080@w5g2000hsg.googlegroups.com">news:1180885823.336051.225080@w5g2000hsg.googlegroups.com...
> How do you test if your memory card is DMA compatible?  Is there a
> specific program to use to test this?? or Do you have to do something
> specific to be able to tell.  Just to let you know, I have the
> MicrodriveTurbo which is supposedly DMA compatible.  Any information
> who be greatly appreciated.