Bankswitched bankswitch games? Yes!

[CPUWIZ]

RevEng and me have done it, it was pretty tricky and I'll let Rev chime in on some of the work he had to go through. But the result is that there is a new bankswitching scheme on this planet. I think we'll call it SC1024, it works by banking in and out entire 128K bankswitched games (bank 0-5 @ $8000, bank 6 @ $4000 and bank 7 @ $C000).

[mckafka99]

Woot! Woot! Sign me up for the #2 cart! (Should it come to pass.) Looks great!

[mmervine]

Awesome...I will take one please!

[gorfcadet]

Do want!

[Jinks]

Want 1 please!! Great work!

[Jinks]

What does??" Give as good as you get?" In the description to basketbrawl mean??

[+RevEng]

RevEng and me have done it, it was pretty tricky and I'll let Rev chime in on some of the work he had to go through

Tech details... the games each of the games needed to be patched so the bankswitching scheme used not only 3 bits for 0-7 banks, but also another 3 bits to identify which 128k bank needed to be active during any bank switch.

 

This was easier said than done, since some of the games used their bank value variables for other purposes. And in some cases the value was loaded out of a location in the current bank, rather than a "lda #value" "sta $8000" pair. The MESS debugger was invaluable for this tracking down all of the bank switch hits.

 

The biggest challenge of them all was Ninja Golf. Even when it was seemingly fully patched, it was still hitting the $8003 hotspot with a weird value during it's startup routine.

 

Thanks to the debugger, I found an off-by-1 bug in its initialization code, which caused an indirect address write to try and write to this odd location.

 

Since the original game code uses $9000 as a hotspot, instead of the usual $8000, it looks like they never tracked down the source of this bug, but instead tweaked the hardware to ignore it!

 

anyway, I'm hoping you guys enjoy this collection. We hand-picked the games to try and included some of the rarer 128k games, based on the feedback from the 1st collection.

Edited April 19, 2014 by RevEng

[+RevEng]

What does??" Give as good as you get?" In the description to basketbrawl mean??

http://dictionary.cambridge.org/dictionary/british/give-as-good-as-you-get

 

[Jinks]

http://dictionary.cambridge.org/dictionary/british/give-as-good-as-you-get

 

Thanks

I never heard that term before.

Its British.. ok that explains a lot.. I guess I couldn't be asked to look it up for myself.

[Lynxpro]

That isn't a British-exclusive term. I've heard that for years here in Northern California.

[LidLikesIntellivision]

I would love to have one!

[MAC-42]

Aww, man! Another really excellent project I want a piece of. Looks like I'd better get a second paper route or something!

[DracIsBack]

Sweet! I might be all over this too!

[toymailman]

Count me in for one!

[+iesposta]

I will buy one to go with my Multicart #1 please. I don't have any of these games.

 

Once Harmony Concerto arrives and my XM module ships, I foresee ending my ColecoVision collecting due to lack of funds, time and interest.

[+Mitch]

The biggest challenge of them all was Ninja Golf. Even when it was seemingly fully patched, it was still hitting the $8003 hotspot with a weird value during it's startup routine.

 

 

 

 

Was this related to the hidden joystick test in Ninja Golf?

 

I want one when they are ready to go.

 

Mitch

[Jinks]

Only could fit 8 games? Not complaining.. just asking.

[jaybird3rd]

Very clever! Congratulations on getting the games to work with your new bankswitching design. I remember going through a similar process with the Aquaricart: the games that I included in that cartridge weren't designed with bankswitching in mind at all, so they were writing into the cartridge ROM all over the place (usually because of missing bounds checks, sloppy memory initialization, and other programming errors). I also relied pretty heavily on MESS's debugger to see what was going on.

[Mayhem]

Very interesting indeed... and if there's a cart, yeah, chalk me in for one as well

[CPUWIZ]

Only could fit 8 games? Not complaining.. just asking.

 

One megabyte is the largest chip available in the required footprint.

 

@Jay: Cheers.

[PAC-MAN PRIME]

Amazing! Please add me to the list!

[+evg2000]

add me to the list also, if there is one

[+RevEng]

Was this related to the hidden joystick test in Ninja Golf?

No, the code in question appears to be part of the DLL initialization. It's implemented as a classic count-down loop which should have run from NUMBER_of_ELEMENTS-1 to 0, but instead it runs from NUMBER_of_ELEMENTS to 0.

 

As a result, during the first loop iteration it reaches past the list of RAM locations and grabs some bogus data, which just happens to be within the hotspot range.

 

Easy enough to see now, with the MESS debugger. I imagine back in the day it gave somebody ulcers trying to track it down.

[+Allan]

Did this affect the game at all?

 

Allan

[+SabertoothRetro]

Amazing! Plus, it's great to see some of the rarer titles on cart no. 2. If this is a list, please put me on it.