93 Z disassembly - I have jsrs to non prom location.

[Ludis Langens]

Roger Heflin <rah at horizon.hit.net> wrote:
> I did find some odd code that does jsr into the $5000 range,
> the prom is mapped from $8000-$FFFF, so $5000 would have to be
> built into the computer's internals.    There about 10 of these jsrs
> to different addresses in the $5000 range.  Does anyone have any
> idea what these do?

The $500x addresses are hooks for GM to use when creating vehicle
calibration data.  They allow an extra calibration PROM to be added to
the running system.  The hooks invoke this extra PROM at key locations
such as computing the timing advance and injector pulse width. 
Someplace you should find some code that will disable all these hooks
unless it sees a "JMP $50xx" at one of these hooks.

> There aren't
> any things checking the TCC bit and setting a register in the $1000
> range.

Look for something that sends a byte out the SPI port, or programs a PWM
channel (the code with lots of $D000 and $DFFF constants.)

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/