Re: [cc65-devel] c64 - getting seemingly random chars on screen

[Michael P. <mp...@bl...>]

On 2021-03-02 17:44, Michael Parson wrote:
> On Tue, 2 Mar 2021, gr...@gm... wrote:
>> I'd use watchpoints on the entire screen, like
>> 
>> . watch store 0400 07e7
>> . x
>> 
>> (assuming your screen memory is at 0400)
>> 
>> then when the first wrong character pops up break into the monitor
>> again, and you'll see a list of writes to the screen. find out which
>> one wrote the wrong character, and you know where it happens.
> 
> Thanks, I'll give that a shot.

Took a few tries, but here's where it happens:

#1 (Stop on store 057c)  006 020
.C:222d  91 D1       STA ($D1),Y    - A:4A X:09 Y:14 SP:ee ..-....C   
84639134
.C:222f  AD 86 02    LDA $0286      - A:4A X:09 Y:14 SP:ee ..-....C   
84639134

Right when the piece I clicked on turned red, I also got a red 'I'

222d is in the middle of the subroutine starting at 2229:

.C:2229  05 C7       ORA $C7
.C:222b  A4 D3       LDY $D3
.C:222d  91 D1       STA ($D1),Y
.C:222f  AD 86 02    LDA $0286
.C:2232  91 F3       STA ($F3),Y
.C:2234  60          RTS

Which, according to the generated label file, is '.putchar'

There should only be 1 character being put to the screen at that time,
the red version of whatever character I clicked on, which is happening,
just that the extra & erroneous character shows up too.

-- 
Michael Parson
Pflugerville, TX