disassembly of 6803 code

[Peter Gargano]

Arnaud Westenberg wrote:

> > To understand the ECU code you'll need a lot of information about
> > what the ECU does, as opposed to just what the 6803 processor does.

> I'm not sure what you mean with this, could you explain a little bit
> more? ...

Your disassembly is just a bunch of load, store, and bit twiddling
instructions. As well as knowing what the registers are connected
to in the real world, you'll be greatly assisted by knowing what
the variables and constants are that are used by the program. 

The GM world has an advantage over some in that various "calibrations"
have made their way into the light of day. Knowing what a ROM value
is used for in a calculation is a pretty powerful aid to disassembling 
that code. That's what a "calibration" is; a list of ROM constants with
comments explaining how they're used. 

> By trying to understand what the processor does I would gain
> understanding about the ecu workings or am I wrong here?

This is a bit like trying to visualise a tapestry (EPROM) when all you 
can see at any one time is a close up of 25 cotton threads (listing 
lines).

Peter.
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