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Forums > C64 Coding > keep top 2 rows of screen from vertical scrolling
2021-07-19 03:09
TheWarCriminal

Registered: May 2011
Posts: 16
keep top 2 rows of screen from vertical scrolling

I lost my code from years ago that would keep the top 2 rows of the character screen (1024+80) from vertical scrolling with no flickering. I used it for the BBS I was creating back then. With recent devs in CBASE not performing how I would like it too I have started back recoding that BBS but I need 2 very important things. First off is a no vertical scroll on the top 2 rows. I know CBASE has one but it flickers and is compiled. Would like one in ML or someone point me in a starting direction. The 2nd one is a date ML routine. I know how to check the time and convert it into a readable format but the timer does not hold a date so it keeps resetting at 24hr. Since I am coding this BBS for WinVice is there a way to get the info from the emulated RTC?

I know this sounds like I have no clue what I am doing but when you have been away from c64 coding for 3 decades you loose the knowledge. Just getting reacquainted with BASIC V2 is a hazzle when you are so used to VB.NET behind code. One oh the things that constantly get me is the string setup: BASIC V2 is string$ where as VB.NET is $string. Which ever company decided to screw around with the context should have left it alone.

Any help would be appreciated in this. (I have searched the forums here, Google and Internet Archive c64 Books)
 
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2021-07-21 07:54
ChristopherJam

Registered: Aug 2004
Posts: 1174
As for the reverse not working, you can replace the inner loop
with

SHOWTEXT
    lda #$00
    sta TEXTP

GTEXT
    lda TEXTP
    cmp #$01+79
    beq EXITTEXT
    ldx TEXTP
    lda TEXTm,x
    clc
    adc #192
    sta TEXTOUTPUT,x
    inc TEXTP
    jmp GTEXT

EXITTEXT


Note the "#" before the 192, and the CLC on the line before.

You can also save a few instructions by doing this:
SHOWTEXT
    lda #$00
    sta TEXTP

GTEXT
    ldx TEXTP
    cpx #$01+79
    beq EXITTEXT
    lda TEXTm,x
    clc
    adc #192
    sta TEXTOUTPUT,x
    inc TEXTP
    jmp GTEXT

EXITTEXT


or, shorter again
SHOWTEXT
    ldx #$00
    stx TEXTP

GTEXT
    cpx #$01+79
    beq EXITTEXT
    lda TEXTm,x
    clc
    adc #192
    sta TEXTOUTPUT,x
    inx
    jmp GTEXT

EXITTEXT


then you can drop TEXTP altogether, and move the comparison to the end, and you can almost certainly replace the clc/adc with an EOR, cutting it down to
SHOWTEXT
    ldx #$00
GTEXT
    lda TEXTm,x
    eor #192
    sta TEXTOUTPUT,x
    inx
    cpx #80
    bne GTEXT


Hope that helps.
2021-07-21 10:03
Krill

Registered: Apr 2002
Posts: 1974
If that dubious ADC is intended to invert characters defined as screen codes and copied directly to screen memory, shouldn't it rather be EOR #$80? :)
2021-07-21 11:42
ChristopherJam

Registered: Aug 2004
Posts: 1174
I'm guessing it's also meant to be converting from some other rep to screencodes?

Also, best way to avoid the flicker at the top is probably to clone the kernal routines then patch them to remove the first two rows from the area updated by the scroll code..
2021-07-21 11:44
Groepaz

Registered: Dec 2001
Posts: 9973
Don't forget to patch the HOME location too
2021-07-21 12:35
Krill

Registered: Apr 2002
Posts: 1974
Quoting Groepaz
Don't forget to patch the HOME location too
Or just have prints all ordinary on 40x25, but with a split that would optionally display a hires bitmap in the top two rows (no $d800 issue). Or, well, border sprites!
2021-07-21 12:40
Groepaz

Registered: Dec 2001
Posts: 9973
Oh yeah, border sprites with RS232 NMI going on \o/
2021-07-21 12:47
ChristopherJam

Registered: Aug 2004
Posts: 1174
Quoting Krill
Quoting Groepaz
Don't forget to patch the HOME location too
Or just have prints all ordinary on 40x25, but with a split that would optionally display a hires bitmap in the top two rows (no $d800 issue).


Yes, I think Silver Dream already mentioned raster splits.

(much as you already mentioned stealing the kernal routine - though I was thinking more, disable ROM and patch the kernal routine, so scroll is still triggered by character printing as usual)

Nice idea using hires bitmap to avoid d800 issues though!

I'm still unclear as to whether he wants to do smooth scrolling or just the usual row resolution scrolling.
2021-07-21 12:51
Krill

Registered: Apr 2002
Posts: 1974
Quoting ChristopherJam
though I was thinking more, disable ROM and patch the kernal routine, so scroll is still triggered by character printing as usual
Somebody mentioned memory being tight, so i guess hooking into the CHROUT vector and doing some interception and custom scroll etc. seems more feasible than hogging 8 KB for pretty much the same functionality. =)
2021-07-21 12:54
Krill

Registered: Apr 2002
Posts: 1974
Quoting Groepaz
Oh yeah, border sprites with RS232 NMI going on \o/
Same problem as with a raster split, no? But can be turned off for transfers.

And i guess you wouldn't really use actual NMI but poll the flag from mainline thread instead (for maximum transfer speed)?
2021-07-21 13:46
Silver Dream !

Registered: Nov 2005
Posts: 73
Quoting ChristopherJam
(much as you already mentioned stealing the kernal routine - though I was thinking more, disable ROM and patch the kernal routine, so scroll is still triggered by character printing as usual)
That was actually the very first suggestion I came with. The question is whether RAM under KERNAL is to be used for something else than a KERNAL copy. Hooking through IBSOUT as suggested by Krill is more complex but surely uses less than 8KiB needed for KERNAL patching.

Quote:
Nice idea using hires bitmap to avoid d800 issues though!
Yes, although also rather pricey both in terms of memory and cpu usage.

Quote:
I'm still unclear as to whether he wants to do smooth scrolling or just the usual row resolution scrolling.
Good that it's not only me who has doubts on the actual OP's goal :-)
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