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waterfall: back to where we were, but with jump table

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use rts hack, as 65c02 jmp (ind) has 6 cycles vs 5 on NMOS.  URGH
This commit is contained in:
Vince Weaver 2018-08-03 16:29:12 -04:00
parent f7c66da81f
commit 0bcb7e3934
1 changed files with 43 additions and 47 deletions
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90
waterfall/waterfall.s
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@ -222,10 +222,10 @@ loopB:
jmp display_loop
jump_table:
.word display_odd
.word display_odd
.word display_odd
.word display_odd
.word (display_odd-1)
.word (display_even-1)
.word (display_odd-1)
.word (display_even-1)
jump_addr:
.word $00
@ -245,35 +245,33 @@ jump_addr:
; if odd 10 + 8 + display_odd + 3 (balance) = 21+display_odd
; 3+6
; between 10 + 8 + display_even = 18+display_even
; jump_table
; 39 + display_odd
; 38 + display_odd
; we have 3 (the jmp back)
; = 3 cycles that need to be eaten by the vblank
display_loop:
; inc FRAME ; 5
; lda FRAME ; 3
; and #$10 ; 2
; lsr ; 2
; lsr ; 2
; lsr ; 2
; tay ; 2 ; 18
; lda jump_table,y ; 4
; sta jump_addr ; 4
; lda jump_table+1,y ; 4
; sta jump_addr+1 ; 4
; jmp (jump_addr) ; 5 ; 39
inc FRAME ; 5
lda FRAME ; 3
and #$10 ; 2
;========== new code
lsr ; 2
lsr ; 2
lsr ; 2
tay ; 2 ; 18
lda jump_table+1,y ; 4
pha ; 3
lda jump_table,y ; 4
pha ; 3
rts ; 6 ; 38
;========== old code
beq even
; 2
lda FRAME ; (nop) ; 3
@ -281,7 +279,7 @@ display_loop:
even:
; 3
nop ; (nop) ; 2
jmp display_even ; 3
jmp display_odd ; 3
display_loop_return:
@ -554,27 +552,23 @@ gr_offsets:
; we come in already 21 cycles into things
; so the first scanline is a loss (but that's OK)
; first scanline: 39+ 2 (from ldy) so need to kill 65-41 = 24
; second scanline, again kill so 65 killed
; first scanline: comes in with 38
; second+ scanline need to kill 65
display_odd:
odd_first_four_lines:
; line 0
; 18/ 21 / 39
; 38
ldy #4 ; 2
asl DUMMY ; 6
asl DUMMY ; 6
asl DUMMY ; 6
asl DUMMY ; 6
asl DUMMY ; 6*
asl DUMMY ; 6*
asl DUMMY ; 6*
lda YPOS ; 3**
lda YPOS ; 3
nop
nop
; line 1, 65 cycles
@ -913,27 +907,30 @@ display_even:
even_first_four_lines:
; we do mockingboard here
; we have 239 cycles (65*4 = 260 - 21 = 239)
; we have 222 cycles (65*4 = 260 - 38 = 222)
; 78+78+2+20 = 178
; 239 - 178 = 61 to kill
; come in with 18
; 18
; kill 142
; 38
; come in with 38
; 222 - 100 = 122 to kill
ldx #12 ; 2
; kill 122
ldx #10 ; 2
dummy_loop:
asl DUMMY ; 6
dex ; 2
bne dummy_loop ; 3
; 9 left over
; -1 exit loop
; 11 left over
nop ;2
nop ;2
nop ; 2
lda XPOS ; 3
lda XPOS ; 3
lda XPOS ; 3
; high = 5 + 12+ 3 = 20
; medium = 5 + 9 + 6 = 20
@ -944,7 +941,6 @@ dummy_loop:
; cmp OLD_XPOS ; 3
; beq skip_mb ;
; 2
; sta OLD_XPOS ; 3
cmp #23 ; 2
@ -1253,7 +1249,7 @@ ground_loop_even_done:
nop ; 2
jmp display_loop_return ; 3
; rts ; 6
.align $100