[Coco] Writing a CPU simulator for the 6809

[Mark McDougall]

Emulating the other hardware is no different to emulating the CPU. I'm having some difficulty understanding how you're comfortable with the idea of software emulation of a CPU but not a VDG!?!



Sent from my ASUS Pad

Tony Cappellini <cappy2112 at gmail.com> wrote:

>I recently saw a presentation where the presenter wrote an Apple 2
>simulator in Python. I thought this was pretty even though the actual demo
>was very minimal.
>His project claims that he is able to run many Apple Basic programs. I
>thought this would be a fun project to do for the 6809.
>
>Looking at the source code it's somewhat straightforward how he did this,
>but I am puzzled when it comes to executing the Basic ROM.
>
>I know VCC executes COCO ROMS, as do MAME, MESS, and other emulators.
>
>What I don't understand is-
>ROMS typically have to initialize the hardware. Interrupt vectors need to
>be setup (usually in RAM), memory tests are done, I/O chips need to be
>programmed, etc..
>
>Since the emulators are in software, none of this hardware exists.
>I don't understand how one would attempt to write software to simulate a
>hires graphics screen, while maintaining the timings that the VDG normally
>handles.
>
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