Date   : Tue, 23 Aug 1994 11:33:40 WET DST
From   : Bonfield James <jkb@...>
Subject: Re: Mine did something! Eeek!

Chris Lam writes:

>beeb snapshot formats were discussed a while back. naturally the contents
>of the paged io needs to be dumped but what is dumped will depend on
>how you emulate the hardware. therefore to get one snapshot to work on
>more than one emulator is probably unlikely unless an overall strategy is
>agreed upon.

See James Fidell's emulator for the Snapshot format. His is as good a format
as any so we may as well use it. It does has space reserved for the vias.

>my philosophy for handling the paged io is to do all the emulation when
>values are STORED to sheila. therefore any reads from sheila will be 
>correct and one does not need to 'intercept' the read.

This won't work too well. Data on the 6522 lines can change between your last
write and your read - such as by someone pressing a key. It probably only
works for you as the 6502 code you tested (ie the OS) had writes and reads
very close together in time.

>a really invaluable (but somewhat unheard of) book is 'guide to the bbc
>roms' by don thomasson, published by melbourne books. there wasn't a hope
>in hell of me getting this far without it.

Is it any better than the Advanced User Guide?

       James