Re: [stella] Question about SWCHB

[zu03776 <zu03776@xxxxxxxxxxxxxxxxxx>]

> > Does this give him  an extra bit for RAM or something?
>
> I thought I found the answer to my question in  the archives from a 
> similar question asked by Adam Wozniak. http:/ 
> /www.biglist.com/lists/stella/archives/200404/msg00412.html
>
> Does anyone know if SWBCNT has any  use?

Yes, it does.  You can store #$34 into SWBCNT and get three extra bits 
of RAM in the unused bits of SWCHB.

I just played this ROM on Stella 1.2, and the P0 sprite is solid.  
After compiling MakeWav for the Mac, and putting it on the Supercharger 
on my Atari 7800, I received a line with holes in it, as expected.  So, 
which does Z26 do?

Basically the line on the left of the screen shows the bits of SWCHB on 
the screen.  If you toggle the A/B switches, B/W color switch, select, 
and start, you'll see some lines disappear.  I'm not terribly fancy 
with displays.

During the display loop, I count down the scanlines using Y from 192 to 
0.  For each scanline, I store the current value of Y into SWCHB, then 
read the value back out of SWCHB and store it into GRP0.

The lines of interest are flagged with ***** MORE BITS ***** comments.

If you wondered, I've been working on a ROM to play various nursery 
rhymes, and was working to understanding Paul Slocum's music driver by 
writing my own.  The example code was just placed in the video display 
of this ROM.

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