[Coco] Writing a CPU simulator for the 6809

[Tony Cappellini]

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.