[stella] Any guru to solve a problem with the ROL instruction ?

Subject: [stella] Any guru to solve a problem with the ROL instruction ?
From: Christian Bogey <khryssun@xxxxxxxx>
Date: Sat, 17 Apr 2004 20:38:46 +0200 (CEST)
Hi,
I wrote a little demo to try to make some effects 
using playfield and I've got a bug in my program 
but I can't find why it occurs :-(

Maybe one of the 6502 gurus here may help me ;-)

I'm using the ROL instruction to modify the patterns
of PF0 and PF2 (I'am using shadows number in ram) and
I noticed :

* Using the ROL instruction 1 time gives a good
result.
* Using it 2 times makes a total mess in the Playfield

  display.
* Trying to compile with the first line only, gives a 
  good result (ROL PF0 Value).
* Trying to compile with the second line only, gives a

  good result (ROL PF2 Value).
* Trying to compile both lines and it's a total mess !
* BTW I noticed the problem doesn't occur if I'm using

  ROL for the 1st line and ROR with the 2nd (maybe a
  hint to find the cause of the problem ?)

Does anybody can explain me where I'am wrong ??? 

I've join the source : the bug is located under the
line 103 labeled :

;-------------- PROBLEM STARTS
HERE--------------------



Thanks,

Chris


	

	
		
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