> Well, sending stuff to the 2600's screen could be as simple as a six-digit
> score routine, I think... and once working, it can be used for all the
> modules. If you can get a disassembler to work, it doesn't sound all that
> difficult.
Most you'd get out of me is a green screen if it passed, and maybe that in
between channels look if it failed! Speaking of which, have you ever played
with turning the Atari on and off without a cart in the slot? Amazing how
often the display syncs. It's like air has vsyncs and vblanks in all the
right places. ;-)
> "Parasite"? More of a symbiont ;) The point is the fast CPU doesn't need
> to be synced to the 6507. It just holds the 6507's data lines to the
> opcode for NOP until it wants the 6507 to do something... then it delays
> the appropriate amount of time between parts of the 6507 instruction.
Hmmm.... Maybe. But how do you know when the 6507 *sees* the new
instruction that you put on the bus? You'd need a pretty good idea so you
could delay the right time between parts of the instruction. And how do you
know when it's safe to change the instruction? If the host samples the data
bus just when the instruction is changing it *might* see garbage and it
*might* get lost.
>
> > > And you'd need either some way to reverse the interface, so
> > > the fast CPU could read controlller and switch input from the
> TIA, or just
> > > plug the controllers into the cart, with an extra I/O chip.
> >
> > Just feed it the instructions to read the switch inputs, and
> watch the data
> > go by on the bus.
>
> Er, what bus? The new CPU has its own private memory bus... where are we
> gonna connect the 6507 data bus to the new CPU?
Oh, through some I/O ports on the symbiont. The symbiont could watch or
drive the 6507 data lines at will, and it could watch the address lines too
if it wanted. But you'd need a pretty fast symbiont to get the timing
accurate enough for this to actually work. I really think you'd need
dual-ported RAM to get anything like this to work with reasonably
inexpensive technology. Have the symbiont fill the RAM with a frame's worth
of instructions at a time. Then cycle by cycle synchronization between the
CPUs becomes less important and you have more CPU cycles for doing the game
calculations.
So in this scheme, the host would read the switches and store the results
somewhere in RAM for the symbiont to see maybe once per frame...
John
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