Stock chip - unused locations

[dennisL]

The other day, Carl I. mentioned he always wanted to look at the listing to determine which locations where not being used, so he could plug in patches. However, he just never found the time to do it. I'm thinking there might be other "chip hackers" who also could benefit from this info. So here are the unused locations in the 86/87 chip:
Data Section
$271: Boost Spark Filter Coefficient
$27E & 27F: (some blinky thing for SES light)
$2A2: Malf32 LV8 Limit - not used due to bug in ROM code
$3EF: TCC Lock Min Temp
$42B: Highway Mode AFR
$479 - 4B0: (56 bytes) intended for simultaneous injector C/L
$68E - 690: (3 bytes) IAC stuff
$6FB - 70D: (19 bytes) MAF Table #6
$77D & 77E: leftover CCI timer
$798 - 79E: (7 bytes) 0's
Code Section
$7DC - 7DF: (3 bytes) 0's
$8DA - 8EF: (22 bytes) 0's
$AE5 - AFC: (24 bytes) DFCO AE code that does absolutely nothing
$B1C - B2B: (16 bytes) 0's
$BE3 - BF3: (17 bytes) C/L Vaporization - never executed
$C4C & C4D: load A with airflow # - not used
$D97 - DE1: (75 bytes) simultaneous injector C/L
$F34 - F3A: (7 bytes) simultaneous fuel system
$FFB - FFF: (5 bytes) 0's

The factory code also has AE based on LV8 increase disabled but to reuse this chip space requires many changes to branch addresses and is too much to list here.

Let me know if something on this list is used and I'm just not aware of it.

 

[ijames]

That's great, Dennis. I'll try to confirm your list - that is always much easier than doing the work the first time . Thanks.

 

[BJM]

Dredging up an old post

I was looking at this again and I was wondering. If I simply kill the following:

$AE5 - AFC: (24 bytes) DFCO AE code that does absolutely nothing

and also along with $A4F-$A59 to prevent it from writing to $3F and $40. I think we would have a 2 new adjacent free RAM locations.

Does this make sense?

 

[dennisL]

What I would do is move the jump from $3AFD up to $3AE5. Since it uses a direct address, no change necessary. This gives you $3AE8 - 3AFF to use for your code.

As for $3A4F - $3A59, this code sets the IAC position during DFCO and makes DFCO functional for 1 code pass. If you have disabled DFCO somewhere else, you can certainly reuse this portion of the program.

$40 - can be reused if DFCO is disabled
$3F - be careful here because the ROM program decrements the value at $E85D. If you've disabled DFCO and disabled the code that sets $07 bit 4 (DFCO Active), you can use $3F.