Editing CPU Logic for Pulling a Goalie

[The Sauce 103]

Hi All,

I was wondering if anyone knows how to "re-program" the GENS roms so that if the CPU is down by one goal, in the 3rd, they may pull their goalie.  The logic, now, is that the CPU won't do so unless they are down by 2 (as a min).  I thought I saw it mentioned, once upon a time, on this forum, but can't find it.  Anywho, if anyone knows "the how" and could provide some instruction on how to do it, I'd greatly appreciate it.  It's definitely something I'd like to have in my future roms assuming a novice like me could do it. 

Cheers!

[smozoma 391]

I could guide you through this using the techniques from Tony H's hacking tutorial

https://forum.nhl94.com/index.php?/topic/3474-reference-nhl-94-rom-hacking-school/

The way i would do this would be to put RAM read traces on the goal score RAM values, and then wait for the goalie to be pulled. The last traces on those values must be used to calculate whether or not the pull the goalie.

Then a code trace would reveal the code used to calculate whether or not the pull the goalie.

Probably the code has something like "take the difference of the goals", "test the difference against 2" "if the difference of goals vs 2 is 0, then pull the goalie"

Then we'd try to change the code so it pulls the goalie if the difference is 1 or 2.

You up for that?

[The Sauce 103]

1 hour ago, smozoma said:

I could guide you through this using the techniques from Tony H's hacking tutorial

https://forum.nhl94.com/index.php?/topic/3474-reference-nhl-94-rom-hacking-school/

The way i would do this would be to put RAM read traces on the goal score RAM values, and then wait for the goalie to be pulled. The last traces on those values must be used to calculate whether or not the pull the goalie.

Then a code trace would reveal the code used to calculate whether or not the pull the goalie.

Probably the code has something like "take the difference of the goals", "test the difference against 2" "if the difference of goals vs 2 is 0, then pull the goalie"

Then we'd try to change the code so it pulls the goalie if the difference is 1 or 2.

You up for that?

Admittedly, the second paragraph (and 4th paragraph) is “Greek” to me.  I don’t know anything about RAM read traces.  However, I’m assuming the guide that you linked covers it.  I’m up for trying so I’ll get to reading and see if I can figure it out.  Thanks for the point in the right direction!

[kingraph 644]

Good luck on your journey.  It's a magical place when you start ram searching, tracing and tinkering.  The feeling of when you succeed is glorious.  I think if you like puzzles, you'll enjoy doing this kind of work.  It can get frustrating, but please post any questions you may have.  Happy to help if I can.  

[The Sauce 103]

1 hour ago, kingraph said:

Good luck on your journey.  It's a magical place when you start ram searching, tracing and tinkering.  The feeling of when you succeed is glorious.  I think if you like puzzles, you'll enjoy doing this kind of work.  It can get frustrating, but please post any questions you may have.  Happy to help if I can.  

Unfortunately, this is very greek to me as this requires more of a concept understanding then editing a rom or images. 

I'll play around with this over the weekend when I have some free time.  It's gonna take some time to figure it out as it is a lot of "new" for me.  It's almost like learning a new language.  LOL.  If I have questions, I'll definitely ask.

Edited October 25, 2019 by The Sauce

[Edge of '94 Midwest 168]

I've had the computer pull the goalie on a 1 goal deficit in Gens.

[smozoma 391]

Just try following Tony's tutorial (or the re-written one I did), in which he goes step by step through a simple hack. If you enjoy how it works (like Raph says, it can be very addictive), I can direct you on how to use the same process but with the necessary changes needed to fix the goalie pulling bug.