Subject: Re: [stella] Any guru to solve a problem with the ROL instruction ? From: Darrell Spice <dspice@xxxxxxxxxxxxxx> Date: Sat, 17 Apr 2004 15:11:27 -0500 |
correction - the rotation is the other way, but PF0 is reversed when displayed.
11001100 - 1st line - C is 0, this 0 rolls into bit 0 on the next ROL 10011000 - 2nd line - C is 1, this rolls into bit 1 on the next ROL 00110001 - 3rd line - C is 1, ditto 01100011 - 4th line
and so on.
On Apr 17, 2004, at 2:12 PM, Darrell Spice wrote:
ROL uses the C(carry flag) as an additional bit during the rotate. Looking at just PF0ADR this is what you're getting:
11001100 - 1st line - C is 0, this 0 rolls into bit 7 on the next ROL 01100110 - 2nd line - C is 0, ditto 00110011 - 3rd line - C is 0, ditto 00011001 - 4th line - C is 1, this 1 rolls into bit 7 on the next ROL 10001100 - 5th line - C is 1 11000110 - 6th line - C is 0 01100011 - 7th line - C is 0 00110001 - 8th line - C is 1 10011000 - 9th line - C is 1
if you look closely, you'll see that every other "black diagonal" is a little bit bigger. I suspect you're not wanting this. When you add in PF2ADR the C flag from the ROL on PF0ADR is rolled into the 7th bit of PF2ADR, while the C from PF2ADR is rolled into the 7th bit of the next PF0ADR value.
It might be easer to see the problem if you change your PF0ADR initial value to #%10101010
On Apr 17, 2004, at 1:38 PM, Christian Bogey wrote:
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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