XEGS Bounty Bob giving up

[Wrathchild]

I tried to take to original 40K BB cart image and make this

work using the standard 64K XEGS model. This almost

works but I believe the additional overhead in swapping in

the correct bank pair means that some interrupts overrun

and so the stack/bank selection gets out of control.

 

The original cart uses a clever stack popping method of jumping

to routines so that the (RTS) return restores the state of the

selected banks at the time of the call. However, interspersed

in the cartridge are other bank swap commands. The cart

model is neat - $A000->$BFFF is fixed 8K, but $8000-$8FFF

and $9000->$9FFF are independantly selectable, each having

selecting one of 4 banks via access to the addresses

$8FF6->$8FF9 and $9FF6->$9FF9 respectively.

 

Anyway, the sources of where I'd got to are included if anyone

wants to try and finish this. The problems to fix are:

 

1) When starting the game, the screen scrolls into position.

At a random point the drawing stops and so only part of the

level is displayed and you cannot play. Sometimes the screen

will draw OK and you can play the level.

 

2) When music is played the sound is messed up. I'm not sure

if this is a problem of the correct bank not being selected when

note data is accessed, or if there is some protection in the code

which corrupts the data, e.g. press 'select' to see the high-scores.

 

Good luck,

Mark

BbsbXegs.zip

[carmel_andrews]

'wrathchild'

 

you seem to have forgotten something, if memory serves me correctly looking at the loader of the cassette version, BBSB uses the normal xl/xe bank switching to load of the first part of the code in at page cxxx (it is 'hardloaded'), the main block of code loads in a lo end of mem and is scrambled up...i.e the data loaded into ram doesn't correspond with the data held on the cassete/disk

 

I am assuming/guessing the the BBSB cart version works pretty much the same way

[Wrathchild]

No, the cart would allow you to play on 48K machine,

the tape version is for a 64K machine, so simply porting

that to a switchable XEGS or MegaCart, or even a flashcart

would be more straightforward but would only be good

for XL/XE owners, excluding the 400/800.

[carmel_andrews]

No, the cart would allow you to play on 48K machine,

the tape version is for a 64K machine, so simply porting

that to a switchable XEGS or MegaCart, or even a flashcart

would be more straightforward but would only be good

for XL/XE owners, excluding the 400/800.

918684[/snapback]

 

 

 

 

 

Perhaps certain cart. bank switching protection techniques cannot be defeated and you've probably come across one of them... unlucky you, i guess not even scanalyser or impersonator or the pill or the impossible would be able to defeat this technique (as these programs predated the new cart. bank switching protection techniques, the fact that these programmes did a song and dance in getting 16k programmes to work is irrelevent)