Date   : Wed, 31 Aug 1994 11:25:04 +0000
From   : lamcw <lamcw@...>
Subject: IT'S STARTING TO WORK...

hello again,


lamcw (me) wrote:

;the files copied over okay. well, arcadians may run without any hitches
;but i reckon i just got lucky. i tried WHITE KNIGHT chess program but it
;crashes during its move computation...

sussed it out last night. i was not allowing for 'wraparound' in my addressing
modes. i.e.
   LDX#2
   STA &FF,X

must put the byte in to zero page location &01. Similarly
   LDX#2
   STA &FFFF,X .

wraparound needs to be considered for all the indexed addressing modes.once i'd
done this, WHITE KNIGHT worked fine. the REVS screen is now not-such-a-mess!

*********

David Alan Gilbert <gilbertd@...> wrote:

;> REVS (ha ha) ... wow the screen is a MESS!

;Well it will do won't it - its got to do scrolling - have you allowed changes to
;screen start address?


yes i have. this whole business about changing modes half way down the screen
should not present too much of a problem. it's a case of 'plot as you execute'.
everytime you execute an opcode, process a pixel(s) - just like a real beeb.
when you've reached the 'last' pixel, send the whole picture to the screen.

i also don't believe very precise timing of instructions is required. but it
helps to be reasonably accurate of course.



chris lam.