[comp.sys.atari.st] STe Hardware scroll

micro@imada.dk (Claus Pedersen) (07/10/90)

Hi;

Does anyone know why the STe hardware scroll, won't work in monocrome mode?
-or even better how to fix it (software!!!) :-)

The problem is that this simple program don't work :
	vbl:
	    movem.l d0-d1, -(a7)

	    move #LineLen - N_Planes, D1
	    move Offset, d0
	    addq #1, d0
	    and #%1111, d0
	    move d0, Offset
	    bne no_fng
	    addq #N_Planes, D1
	no_fng:
	    move d1, LINEWID
	    move d0, HSCROLL
	    
	    movem.l (a7)+, d0-d1
	    rte

it's installed as the only program on the vbl, and all other interupts is 
disabled...
N_Planes is 1 for mono, and 4 for Low res...
The program is shortned a bit for the sake of readability (it won't scroll
more than 15 pixels). But it ilustrates the point: the screen moves to the left 
(physical) when HSCROLL becomes 0 (i think it's HSCROLL that triggers the jump).

PS it works fine in low res and the scroll in mono works, if HSCROLL don't
become 0 (which means that LINEWID is constant LineLen - N_Planes). 


- Klaus (micro@imada.dk)