The code is extremely complex, and this is some of the earliest and simplest! GM learned a lot along the way and incorporated that knowledge into the later versions. Also things got a lot more sophisticated with the sequential injection, multiple O2 sensors, etc.

I think the average person is much better off staying at the high level of the tuner software. Getting down to the "bare metal" is a LOT of work.

This code was disassembled and commented back in the mid '90s. The author didn't take credit for his work, but my guess is that it was Ward Spoonemore who did the original work (from this comment: "REV 8/1/95, WS"). I think he posted it originally on his web site, which is long gone. Some of the comment style is different, so I think somebody else also contributed, possibly Bruce Plecan. These guys are both gone so there is no way to find out for sure.

The original disassembly and commenting must have been an enormous undertaking. I have spent probably 9 months on this and I had a HUGE head start. There are still areas I don't understand and many of the status bits are still mysteries. I have also seen that some of the later "hacs" were based on the $32 code and the errors were propagated along with the good parts. Here is a good example of that:

Original comments:
When I first saw that I thought, "That can't be right. A lower frequency will have a longer period and the count should be HIGHER". After a lot of code analysis, these are my revised comments:

As you can see, the frequencies are different and reversed. We know that the VATS frequency is nominally 30Hz, which would be outside the frequency range of the original comments (33 to 66 Hz). This error has been repeated over and over in later hacs.

In case you're wondering ;-), here is where the numbers come from:
Counter frequency is 65536 Hz. Inverting gives a period of 15.258 us. Multiply 15.258 us * 3277 = .0500 s. Inverting that gives 20.0 Hz. Another way to get there is to divide 65536 by 3277, but that's not the way the code does it.

 

Interesting thread! I originally relocated the MAT because I ported the plenum and it stuck up right up in front of a runner port. Plus if it went bad it would be a chore to change. Since then I have the miniram with no place to put it without tapping a port. I find it interesting to see the temp when data logging. I have been using 32b for tuning lately. Are you going to release a new hac based on your work?

 

My work is all posted on my web page. I update it every time I make a change, which is almost every day. Here's the link:

http://home.earthlink.net/~cliff_har...5/BUA/BUA.html