Re: DMA at 2.8 MHz?

[glynnet@zero.cypher.com (Glynne Tolar)]

In article <C6zDML.M8G@news.cso.uiuc.edu> dat33228@uxa.cso.uiuc.edu (Derek A. Taubert) writes:
>glynnet@zero.cypher.com (Glynne Tolar) writes:
>
>>Here is a thought.  If indeed some devices cad DMA at 2.8 MHz could we modify
>>our motherboards to do DMA at 2.8?  I keep thinking of the 1MHz line needing
>>to be replaced with a 2.8.  I'm going to have to sit down with the hardware
>>reference and see why DMA works and if there is a source for 2.8.  Interesting
>>project!
>
>Without modifications, it _might_ be possible based on a few things.  This will
>give you some direction in your hardware reference hunting:
>
>1) Find out what the following lines are doing during 2.8 MHz operation:
>
>   Part 2 -> ABDIR.L, ABENB.L, DBDIR.L, DBENB.L 
>   Part 7 -> MDIN/OUT, EN425.L
>
>2) Figure out what relation the 2.8MHz clock has to the 7M signal.
>
>But the hardware reference won't help you with this.  I posted this a while ago
>with no luck finding an answer:
>
>] Can anybody provide me with an explanation (or a timing diagram) of what
>] happens on the GS's 1MHz expansion connectors when the processor is screaming
>] along at 2.8MHz?  Phase 0 to the slots comes from the slotmaker (BPH0), and is
>] always as 1MHz.  Technote reference, maybe?
>
>Answer these questions, and I'll personally provide you with a spec. for doing
>2.8MHz I/O and DMA.  If you don't have any luck, I'll probably have the answers
>in about a week when I get my GS into the lab (gotta love 200MHz logic
>analyzers).
>

Hay!  A logic analyzer would help!  Let me know what you come up with.

>The other thing to consider, of course, is what kind of havoc DMA at 2.8 MHz
>is going to reek on the DRAM refresh scheme (or vice-versa)...
>

To make things worse what effect would it have on a ZipChipGS or a Transwarp GS?
Drew at CVT says the Transwarp can't even handly RDY when the GS is in 2.8MHz
mode.  A little incompatability there.

-- 
Glynne Tolar                                      glynnet@zero.cypher.com
                                               or GEnie: G.TOLAR