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Re: Microsoft Softcard and IIgs
Steven Hirsch wrote:
Alex Freed wrote:
vladitx wrote:
I'd guess that screen scroll suffers from this.
Maybe it does, but it doesn't have to. In fact I think it could be
made to work much faster than with the shared memory.
Suppose the whole "terminal emulator" is implemented on 6502 - maybe
just the ROM routines are used. Then the z80 will only issue a (single
byte?) command "scroll the screen" and continue whatever it was doing
while the 6502 does the scrolling at the same time. It will finish and
signal "ready" to z80 to process the next request.
Unfortunately, the stock Applicard OS is too dumb to do this
asynchronously. I implemented something like that to speed up the
CardZ180, though.
Why does the Z80 card even need to know about it? The 6502 code
could always buffer output and appear "ready" unless the buffer is
full. Of course, that's one more copy to get it in the right place
in the screen buffer...
Another guess is that
probably GBASIC doesn't work on Applicard?
I honestly don't know. I would sooner saw off my left arm than use
BASIC for anything, so I'm the wrong person to answer that.
I think I read that some trick allows MS basic to work but no graphics.
I'm guessing that Microsoft used the same hack in all tools shipped with
the Softcard to prevent them from working in other environments. I have
seen patches for Microsoft Fortran and the ALDS cross-assembler to work
around it (the latter is absolutely vital to setting up a native build
environment, IMHO).
In this case, it's simply a matter of the Z80 graphics routines not
having access to the Apple II screen buffer in RAM. A driver could
be written to have the 6502 "proxy" graphics updates, but that would
be relatively slow in comparison with DMA access.
-michael
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