Date   : Mon, 28 Nov 1994 11:20:54 +0000
From   : jfid@... (James Fidell)
Subject: Re: snapshots

Mike Borcherds wrote:

> Has there been any development in snapshot formats?
> How many people have developed their own and how many people are
> using the xbeeb one?

I've not seen anything other than my proposal.

> I would prefer to see a more extensible format, with each bit of the format
> being optional - ie it has a few flags, one for main memory, one for
> each sideways ROM socket, one for each bit of hardware that is memory
> mapped, etc, specifying whether that part has been saved.

I've allowed for that, in a way.  I consider the most important thing to
be that we agree on a set of magic numbers, so that as the snapshot format
evolves, it's possible for the emulator to correctly load the snapshot.

My main concern in posting the suggested spec. was that we could all
discuss a suitable format and not waste time coding all sorts of
incompatible formats.

> (and support for master 128 snaps)

I don't know much at all about this machine, so I couldn't provide for
it in my suggestion.

> Maybe each bit should have a length associated with it, so you could for eg 
> have a snapshot that was just a screen shot without wastage etc

That's not an unreasonable thing to want to do.  However, I didn't
consider it necessary for a first pass, since it made the work of decoding
the snapshot more complex whilst minimally reducing the amount of disk
space required to store them.  Disk space isn't exactly the problem it
was three or four years ago, is it ?

> I very much like the snapshot starting &BC &BB

I suggested starting with &0BBC stored lo-hi, followed by a 16-bit version
number.

> If the timers are in one-shot mode, presumably  we also need to save 
> whether they have "gone off" or not?

I believe that my format will handle this properly because it saves the
full state of the VIAs and a count of the number of outstanding interrupts
(ie. +1 for every piece of hardware trying to pull down the CPU NIRQ line).

If there's interest, I can re-post the spec. that I'm using.

James.

-- 
 "Yield to temptation --             |     jfid@...        
  it may not pass your way again"    |  http://www.mfltd.co.uk/~jfid/
                                     |
        - Lazarus Long               |              James Fidell