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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. :mrgreen:

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 :D
So the fix should be LD H, (HL)
Why is this the solution? :o 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 :D
So the fix should be LD H, (HL)
Why is this the solution? :o 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.... :lol:
REDSINC.P
(2.11 KiB) Downloaded 251 times
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
did i forget to mention it works very well on eightyone V1.7 :mrgreen: :mrgreen: :mrgreen:

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!