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split: have it consistent, no vapor lock yet

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This commit is contained in:
Vince Weaver 2018-07-05 14:03:25 -04:00
parent 18aff6dcad
commit dcb65dc471
2 changed files with 104 additions and 16 deletions
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24
split_screen/calc_freq.c Normal file
View File

@ -0,0 +1,24 @@
#include <stdio.h>
int main(int argc, char **argv) {
int x,y,cycles,desired,range=10;
// desired=3116;
// desired=4152;
// desired=5196;
desired=4547;
printf("You want %d cycles\n",desired);
for(x=0;x<255;x++) {
for(y=0;y<255;y++) {
cycles=1+5*y+y*(5*x+1);
if (((cycles-desired)<range) && ((cycles-desired)>-range)) {
printf("Try X=%d Y=%d cycles=%d\n",
x,y,cycles);
}
}
}
return 0;
}

96
split_screen/credits.s
View File

@ -116,7 +116,25 @@ line_loop:
jsr wait_until_keypressed
;=====================================================
; attempt vapor lock
; by reading the "floating bus" we can see most recently
; written value of the display
; we look for $44 (which is the green grass on low-res)
;=====================================================
; See:
; Have an Apple Split by Bob Bishop
; Softalk, October 1982
vapor_lock_loop:
;=====================================================
;=====================================================
; Loop forever display loop
;=====================================================
;=====================================================
display_loop:
; each scan line 65 cycles
; 1 cycle each byte (40cycles) + 25 for horizontal
@ -137,12 +155,22 @@ display_loop:
; text
bit SET_TEXT ; 4
ldy #15 ; 2
; want 3120-4 = 3116 cycles
; inner loop = 2+(x*5)-1 = 5x+1
; outer loop = 2+(y*5+y*inner)-1 = 1+5y+y*(5x+1)
; 1+5y+5xy+y
; 1+6y+5xy
; 1+y(6+5x)
; Try X=11 Y=51 cycles=3112 (R 4)
lda #0 ; 2
lda #0 ; 2
ldy #51 ; 2
loop2:
; 5*255+2 = 197
ldx #39 ; 2
ldx #11 ; 2
loop1:
dex ; 2
bne loop1 ; 2nt/3
@ -150,16 +178,24 @@ loop1:
dey ; 2
bne loop2 ; 2nt/3
;=============================================
; hgr
bit HIRES ; 4
bit SET_GR ; 4
ldy #15 ; 2
; want 4160-8 = 4152 cycles
; 1+y(6+5x)
; Try X=91 Y=9 cycles=4150, R2
lda #0 ; 2
ldy #9 ; 2
loop3:
; 5*255+2 = 197
ldx #39 ; 2
ldx #91 ; 2
loop4:
dex ; 2
bne loop4 ; 2nt/3
@ -167,17 +203,25 @@ loop4:
dey ; 2
bne loop3 ; 2nt/3
;===========================================================================
; gr
bit LORES
bit LORES ; 4
ldy #15 ; 2
; want 5200 - 4 = 5196 cycles
; 1+y(6+5x)
; Try X=17 Y=57 cycles=5188, R8
lda #0 ; 2
lda #0 ; 2
lda #0 ; 2
lda #0 ; 2
ldy #57 ; 2
loop5:
; 5*255+2 = 197
ldx #39 ; 2
ldx #17 ; 2
loop6:
dex ; 2
bne loop6 ; 2nt/3
@ -185,6 +229,26 @@ loop6:
dey ; 2
bne loop5 ; 2nt/3
;========================================================================
; vertical blank
; want 4550-3 = 4547 cycles
; 1+y(6+5x)
; Try X=13 Y=64 cycles=4545 R2
lda #0 ; 2
ldy #64 ; 2
loop7:
ldx #13 ; 2
loop8:
dex ; 2
bne loop8 ; 2nt/3
dey ; 2
bne loop7 ; 2nt/3