Re: [stella] Star Fire: 1 step forward 2 steps back :-)

Subject: Re: [stella] Star Fire: 1 step forward 2 steps back :-)
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Sun, 1 Dec 2002 15:07:55 +0100
> It's a little convoluted, but it makes nice use of the BRK instruction and
> it saves a few bytes of ROM.

Putting BRK instructions on the bankswitching hotspots is not
going to work that well. Remember that the 6502 always reads
at least two bytes for every instruction. So a BRK at $FFF8
will trigger both $FFF8 and $FFF9 with a one cycle gap. You
could put one of the BRKs at $FFF7, but if Manuel wants to
switch to F6 bankswitching, which he seems to be prepared
for judging by the fact that left all nessessary bytes free
for that, that won't help anymore either.

It's probably best to just waste another 6 bytes in both banks
and have special switching code for the startup routine. If
you can put the access to the hotspot just in front of where
the init code is in the other bank, you could probably get away
with only 3 extra bytes for the BIT instruction.

BTW, the startup banks for some of the bankswitching schemes
was changed for the second version of Playbin. I'm not sure if
Bob added that change to Makewav, but you probably can select
that value with the command line switch for the bankswitching

Ciao, Eckhard Stolberg

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