Re: VGC Chip

[Mark McDougall <markm@vl.com.au>]

Henry wrote:

> Since 
> we're dealing with 20 year old IC's most basic analyzers will work just 
> fine.  Now we just need to wait about 7-10 years and pick one up one on eBay 
> for cheap!  Once that happens then most if not all the 'secrets' of the IIgs 
> will be unlocked and anyone will be able to use the info.  Sooner or later 
> I'll probably start sending stuff off to be cracked anyway.


What you're referring to is a technique known as 'black box reverse 
engineering'. It involves, as you describe, hooking up test equipment to 
all inputs and outputs and attempting to derive the internal 'schematic' 
by analysing the outputs generated by a set of known inputs.

This is actually quite straightforward - for combinatorial logic. Once 
you introduce *states*, then complexity increases exponentially at 
least. And by 'states' I mean any sort of memory, such as explicit 
memory used in registers, scratch ram etc, or implicit, such as state 
variables in a state machine.

Of course, the job is easier when you know *what* the chip does, and 
have *some* documentation on how it works (register map, etc). But it is 
quite difficult to use this information effectively in an automated process.

I suspect you won't learn *anything* useful at all about the VGS with 
any sort of logic analyser that wouldn't be more readily apparent from 
studying the source code of a IIGS emulator.

The 'cracking services' are pretty high-end and AFAIK still involve some 
considerable human effort by experienced engineers. You have to have a 
good understanding of how common logic constructs are implemented at the 
chip level in order to recognise patterns and interpret the results. Way 
out of the realm of a hobbyist hacker, who may not even be capable of 
understanding or using the results!

If you were looking to mass-produce a clone with a market of 100K units 
then it may be worth your while. I also suspect the $4K starting price 
would be for a small support or security chip.

Regards,

--
Mark McDougall, Engineer
Virtual Logic Pty Ltd, <http://www.vl.com.au>
21-25 King St, Rockdale, 2216
Ph: +612-9599-3255 Fax: +612-9599-3266