On Thursday, August 10, 2017 at 8:08:57 PM UTC-4, Harry Potter wrote:
> On Thursday, August 10, 2017 at 3:48:55 PM UTC-4, chitselb wrote:
> > If you needed 141 bytes of zero page on a C-64, what addresses
would you use?  BASIC is switched out, Kernal is still switched in, so
anything BASIC uses can be reallocated.  Having it all be contiguous so I
can go in and out of BASIC is important 
too.
> > 
> > On a PET (4.0 ROM) I'm just using $00-$8C (everything below jiffy
clock) and there's a little ML routine ('aloha') to swap the half page in
and out, but I want to port PETTIL to the C=64
> 
> On a C64, the BASIC ROM uses ZP addresses $02-$8F, but you can use
kernal ZP locations you don't need in your program.  For example, $83-$8B
and $AE-$B6 are used for tape and RS232 and $F7-$FF are for RS232 and free
space.  Does this help?

It looks like what they did is put the memory mapping I/O port at $00-$01
and moved everything up by two?  Does it still have the problem of
occasionally pooping on address $10 ? There are a couple of places in the
PET ROM where writes to $10 occur e.g. 
B3D8 STA $10 , even though Raeto's "Programming the PET/CBM" book
says no, it is unused

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