Re: Choplifter, still no go on Apple IIc +

[Tom Greene <tom@cowgod.org>]

On Jun 27, 3:22 am, mdj <mdj....@gmail.com> wrote:
> On Jun 20, 10:39 am, Tom Greene <t...@cowgod.org> wrote:
>
> > > So, any other ideas?  It'd be great to hear that someone has this
> > > working on iic+ before I put more time frittering into it!
>
> > I just dug out my IIc+ and Choplifter disk and I am seeing the same
> > problem. It also hangs sometimes when only the chopper is firing and
> > no tank is nearby.
>
> Hmmm.... Both those events cause the game to produce sound. Has anyone
> tried it with the sound turned off (probably ctrl-S or something) ?
> The less soft-switches it hits, the less likely to cause a problem...
>

I was actually just poking around some more and it seems like the
problem is indeed related to the sound effects. Looking at the code,
it sends audio to both the speaker and the cassette output. The
cassette output at $C020 seems to be what's fouling things up, though
I have no idea why this would be the case.

There are four locations which reference the cassette output using a
BIT $C020 instruction. If I replace the each of those instructions
with NOPs, the game runs fine. I was able to get it running under
ProDOS by doing:

]CALL -151
*BF58: C0
*BLOAD CHOPLIFTER
*3BEC: EA EA EA
*3BFA: EA EA EA
*3DBE: EA EA EA
*3DDE: EA EA EA
*7FDG


Tom