Date   : Thu, 05 Oct 2000 09:51:10 +0100
From   : "Rich Talbot-Watkins" <Richard_Watkins@...>
Subject: Re: 6522 VIA

Michael Foot <mikef@...> wrote:

> OK, for starters I've put together a 'C' code style notation of how I
> think the 6522 VIA is emulated in code. It's not 100% correct by any
> means and it's also missing bits of the timing like clock stretching
> when the VIA is accessed. It will work with the majority of bbc software
> out there but there are still some games (like Rig Attack) where it won't.

If you have a look back at the code that James Fidell posted to this group a
while back for cracking the Alien 8 protection, you'll be able to see exactly
how the cycle stretching works, even for 'difficult' instructions such as ROL
&FExx.

Cheers,
Rich
Rich Talbot-Watkins
Sony Computer Entertainment Europe, Cambridge.
Richard_Watkins@...