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change border color for a part of the screen
File: HBL.ASM
Intended for use with an Atari ST.
Author: Johan Sorensen, Lund, Sweden
This is a Public Domain horisontal blank routine source example.
Example of application: change border color for a part of the screen
The source code is not very well documented, but it may help some lost soul with his (or her) own programs, as I have gathered that the Atari ST:s interrupt structure is not all that simple to grasp for beginners.
Written originally for use with Metacomco macro assembler.
Observe that if you assemble this file in its original state, it will NOT work as a stand-alone program. This source-code is intended for you to modifify and include into other programs.
IERA: EQU $FFFA07
ISRA: EQU $FFFA0F
IMRA: EQU $FFFA13
IMRB: EQU $FFFA15
TBCR: EQU $FFFA1B
TBDR: EQU $FFFA21
TEXT
insthbl:
movem.l d1-d7/a0-a6,regsav
pea _insthbl
move.w #38,-(sp)
trap #14
addq.l #6,sp
movem.l regsav,d1-d7/a0-a6
rts
_insthbl:
bclr #5,IMRB ;disable 200 Hz clock
move.l $70,__savvbl+2
move.l #newvbl,$70
bsr.s vsync
bset #5,IMRB
rts
vsync:
move.l $466,d0 ;_frclock
vsyncl:
cmp.l $466,d0
beq.s vsyncl
rts
newvbl:
clr.b TBCR
move.l #newlrc,$120
move.b #50-4,TBDR
move.b #8,TBCR
bset #0,IMRA ;Interrupt mask register A
bset #0,IERA ;Interrupt enable register A
move.b #4,TBDR
move.l __savvbl+2,$70
__savvbl:
jmp $fc0634
newlrc:
move.b #20-4,TBDR
move.l #newlrc1,$120
bclr #5,IMRB
bclr #0,ISRA
rte
newlrc1:
move.w #$642,$ffff8240
move.b #4,TBDR
move.l #newlrc2,$120
bset #5,IMRB
bclr #0,ISRA
rte
newlrc2:
move.b #200-20-4,TBDR
move.l #newlrc3,$120
bclr #5,IMRB
bclr #0,ISRA
rte
newlrc3:
clr.w $ffff8240
move.b #4,TBDR
move.l #newlrc,$120
bset #5,IMRB
bclr #0,ISRA
rte
END
