vladitx wrote:
Definitely the PCPI design takes the least-resistance path and decouples the Apple II and the Z80 system as much as possible, at the cost of losing the direct access to Apple II memory.
And why is that a problem?
I'd guess that screen scroll suffers from this. Another guess is that probably GBASIC doesn't work on Applicard?
Actually, with a good software implementation the screen scrolling is far quicker with a decoupled coprocessor. The host processor has control all the time and simply needs to read bytes from a port and write them to the screen. With the softcard, regardless of who is writing to the screen (and I don't recall offhand whether this is 6502 or Z80 code) they share bus cycles with the other guy.
PCPI actually missed a few opportunities for improving performance in this area, but out of the box it's quicker than a softcard. When I did the CardZ180 BIOS, I was able to able to trim a lot of overhead from screen output and it could easily keep up with a 19k2 baud modem. Stock Applicard would drop characters in this mode and the Softcard was hopeless.
Add an accelerator to the host and sky's the limit. You cannot use an accelerator with a DMA device. Applicard works with any accelerator on any version of the A2.
I have a ROM1 GS and a SoftCard clone. If you want I can test it.01 and 03 should be identical in the slot operations, but yes, if you find the spare cycles and feel interested - please do. I will dedicate a day (no plans, though) to plug the analyzer in IIe and IIgs and see what's wrong. M$ SoftCard is the only DMA card I have so far.
There were very few A2 cards that used DMA. The only others I can think of are the Transwarp I (DMA with a vengeance - once it grabs on, it doesn't ever let go) and the Vista 8" floppy controller.
Steve