Re: RamFAST, //e, Zip8, and DMA

[hirsch@ibm.net (Steven N. Hirsch)]

Nancy Crawford (nancyc@pro-aplbytrs.pro-nsdapple.cts.com) wrote:
:  
: Do you have any notes about what was done to your Rev 'B' in order for it
: to properly talk to your Zip8? If I remember correctly, Hugh said
: Sequential didn't have any paperwork on the needed change.
:  
: Heaven knows there are people who would like to be able to use their //e,
: late-model RamFAST, 8Mhz Zip Chips _and_ do DMA.
:  

There is probably no reasonable way to use DMA transfer with a
ZipChip.  However, there was a hack which provided a 2x speedup when
using port I/O.  Normally, the software loop which moves data between
memory and the RF card executes in the C800 ROM expansion area.  As
such, it is never cached by the ZipChip; it runs at normal IIe speed.

The trick is to copy the software loop into the 6502 stack page and
execute it there, where it _will_ be cached and accelerated.  This was
suggested by one of the original developers of the RF card, BTW.  I
wasn't aware that Jawaid had ever implemented it.

Steve