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Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Mon Sep 11, 2017 6:02 pm
by PokeMon
Andy Rea wrote: ↑Sun Sep 10, 2017 10:35 pm
since as hl is stored after this instruction
A bit of all, H is (re)stored after this instruction.
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Mon Sep 11, 2017 6:23 pm
by olofsen
Thinking about a "claire.p" that shows a "thumbs up" path in the Live Memory View...
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Tue Sep 12, 2017 4:58 pm
by zsolt
Hi,
dr beep wrote: ↑Sun Sep 10, 2017 10:22 pm
sirmorris wrote: ↑Sun Sep 10, 2017 6:59 pm
Also,
Code: Select all
L0237: LD B,(HL) ; (7) Note. Harmless Nonsensical Timing weight.
Is exactly it
So the fix should be LD H, (HL)
Why is this the solution?
This is same memory reading.
Zsolt
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Tue Sep 12, 2017 6:25 pm
by dr beep
zsolt wrote: ↑Tue Sep 12, 2017 4:58 pm
Hi,
dr beep wrote: ↑Sun Sep 10, 2017 10:22 pm
sirmorris wrote: ↑Sun Sep 10, 2017 6:59 pm
Also,
Code: Select all
L0237: LD B,(HL) ; (7) Note. Harmless Nonsensical Timing weight.
Is exactly it
So the fix should be LD H, (HL)
Why is this the solution?
This is same memory reading.
Zsolt
The timing must be the same, but B gets a value that is not allowed.
CP (HL) might work too, but it does effect the Z-flag where LD H,(HL) has no effect on flags but still use 7 tstates in 1 command and 1 byte.
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Tue Sep 12, 2017 8:56 pm
by Andy Rea
Just for fun....
regards Andy .
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Tue Sep 12, 2017 10:14 pm
by olofsen
Thanks
I think I'll have it running all night on real hardware - it works quite well even with monitor switched off and eyes closed
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Tue Sep 12, 2017 10:15 pm
by Andy Rea
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Wed Sep 13, 2017 12:39 am
by zsolt
dr beep wrote: ↑Tue Sep 12, 2017 6:25 pm
The timing must be the same, but B gets a value that is not allowed.
OK, it is time-correct, but does not solve the original "problem":
sirmorris wrote:
* Yes, the ZX81 appears to have a pet - a restless red 'ant' (escaped from the classic game?) which relentlessly patrols RAM from the end to the start. It's (most likely) a read instruction in the display routine.
(if it is a real problem)
Andy, what should I see there?
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Wed Sep 13, 2017 12:55 am
by 1024MAK
Well, it's been in the ROM since 1981...
Mark
Re: Charlie's Red Ant - a ROM instruction that reads throughout memory
Posted: Wed Sep 13, 2017 1:03 am
by sirmorris
It's not a problem! It's a pet!