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https://github.com/deater/dos33fsprogs.git
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waterfall: back to where we were, but with jump table
use rts hack, as 65c02 jmp (ind) has 6 cycles vs 5 on NMOS. URGH
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@ -222,10 +222,10 @@ loopB:
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jmp display_loop
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jump_table:
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.word display_odd
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.word display_odd
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.word display_odd
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.word display_odd
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.word (display_odd-1)
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.word (display_even-1)
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.word (display_odd-1)
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.word (display_even-1)
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jump_addr:
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.word $00
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@ -245,35 +245,33 @@ jump_addr:
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; if odd 10 + 8 + display_odd + 3 (balance) = 21+display_odd
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; 3+6
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; between 10 + 8 + display_even = 18+display_even
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; jump_table
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; 39 + display_odd
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; 38 + display_odd
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; we have 3 (the jmp back)
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; = 3 cycles that need to be eaten by the vblank
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display_loop:
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; inc FRAME ; 5
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; lda FRAME ; 3
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; and #$10 ; 2
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; lsr ; 2
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; lsr ; 2
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; lsr ; 2
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; tay ; 2 ; 18
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; lda jump_table,y ; 4
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; sta jump_addr ; 4
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; lda jump_table+1,y ; 4
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; sta jump_addr+1 ; 4
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; jmp (jump_addr) ; 5 ; 39
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inc FRAME ; 5
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lda FRAME ; 3
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and #$10 ; 2
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;========== new code
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lsr ; 2
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lsr ; 2
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lsr ; 2
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tay ; 2 ; 18
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lda jump_table+1,y ; 4
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pha ; 3
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lda jump_table,y ; 4
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pha ; 3
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rts ; 6 ; 38
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;========== old code
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beq even
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; 2
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lda FRAME ; (nop) ; 3
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@ -281,7 +279,7 @@ display_loop:
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even:
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; 3
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nop ; (nop) ; 2
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jmp display_even ; 3
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jmp display_odd ; 3
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display_loop_return:
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@ -554,27 +552,23 @@ gr_offsets:
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; we come in already 21 cycles into things
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; so the first scanline is a loss (but that's OK)
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; first scanline: 39+ 2 (from ldy) so need to kill 65-41 = 24
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; second scanline, again kill so 65 killed
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; first scanline: comes in with 38
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; second+ scanline need to kill 65
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display_odd:
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odd_first_four_lines:
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; line 0
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; 18/ 21 / 39
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; 38
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ldy #4 ; 2
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asl DUMMY ; 6
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asl DUMMY ; 6
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asl DUMMY ; 6
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asl DUMMY ; 6
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asl DUMMY ; 6*
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asl DUMMY ; 6*
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asl DUMMY ; 6*
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lda YPOS ; 3**
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lda YPOS ; 3
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nop
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nop
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; line 1, 65 cycles
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@ -913,27 +907,30 @@ display_even:
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even_first_four_lines:
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; we do mockingboard here
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; we have 239 cycles (65*4 = 260 - 21 = 239)
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; we have 222 cycles (65*4 = 260 - 38 = 222)
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; 78+78+2+20 = 178
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; 239 - 178 = 61 to kill
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; come in with 18
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; 18
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; kill 142
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; 38
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; come in with 38
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; 222 - 100 = 122 to kill
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ldx #12 ; 2
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; kill 122
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ldx #10 ; 2
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dummy_loop:
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asl DUMMY ; 6
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dex ; 2
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bne dummy_loop ; 3
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; 9 left over
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; -1 exit loop
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; 11 left over
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nop ;2
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nop ;2
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nop ; 2
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lda XPOS ; 3
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lda XPOS ; 3
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lda XPOS ; 3
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; high = 5 + 12+ 3 = 20
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; medium = 5 + 9 + 6 = 20
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@ -944,7 +941,6 @@ dummy_loop:
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; cmp OLD_XPOS ; 3
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; beq skip_mb ;
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; 2
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; sta OLD_XPOS ; 3
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cmp #23 ; 2
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@ -1253,7 +1249,7 @@ ground_loop_even_done:
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nop ; 2
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jmp display_loop_return ; 3
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; rts ; 6
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.align $100
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