[Coco] [color computer] Just imagining...
diegoba at adinet.com.uy
Wed Feb 1 10:50:56 EST 2006
That sounds a bit like Sockmaster's CoCo 4...
Mike Pepe wrote:
> I had a couple of ideas. One that comes to mind is to simply let an
> additional CPU to utilize the bus when the primary is idle or busy
> executing an internal instruction. That sounds like what Phill
> mentioned before- a circuit that uses TSC/LIC/BS/BA lines to arbitrate
> the bus (6809E was designed with this in mind)
> The IDMA concept is, of course, what the 6847/6883 combo in the CoCo
> does. E high=CPU, E low=VGA. You can substitute another 6809 to
> operate during E low, or a 6844 DMA controller, etc. Unfortunately
> this won't work in a CoCo since that dead time is taken up by the VDG.
> My plan was to break one cycle into 4 pieces. essentially a 4 phase
> system where each component lags 90 degrees. 3 CPUs can get 3/4 of the
> cycle and the last can be for video/refresh if DRAM is used.
> Unfortunately this needs a lot of latches and 60ns memory!
> Probably something that could be hacked into a FPGA/CPLD array.
> Anyway, that's what I was thinking.
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