[Coco] XRoar Accuracy (was: Introduction)

[Ciaran Anscomb]

Ciaran Anscomb wrote:
> Jayeson Lee-Steere wrote:
> > Following up on an earlier post of mine, I got hold of a USA Coco 1 and a ran
> > it with the Daggorath cartridge. It turns out that XRoar runs it, as best I
> > can tell, perfectly. [...]
> > 
> > Nice work Ciaran, the whole emulator is very well polished. (I'm still
> > looking forward to hooking up the logic analyzer for my work though).
> 
> Thanks!  It's shaping up...  There's still PAL CoCo timing to get right
> (without reducing the HS to an infinitely short pulse!).  And probably
> loads of other things too ;)

... which made for a good morning's work, and all before my first cup
of tea!

http://www.6809.org.uk/tmp/da/pal_coco_probe/

So the deal is, slight difference in the positioning and duration of the
VDG interruptions compared to the Dragon, and most importantly from my
point of view (the bit of information I was missing) - the HS signal fed
to the PIA is *inverted* (as well as continuing during the interruption).

PAL-patched Dragonfire is go :)  If anyone wants to play, here's a
snapshot build of XRoar with the fixes:

http://www.6809.org.uk/tmp/xroar/

..ciaran