[4f508e6] | 1 | | ------------------------------------------------------------------------------
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| 2 | | vbank.s -- VSDD bank switching control functions
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| 3 | | Version 3 -- 1989-12-19 -- D.N. Lynx Crowe
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| 4 |
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| 5 | | unsigned
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| 6 | | vbank(b)
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| 7 | | unsigned b;
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| 8 |
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| 9 | | Set VSDD Data Segment bank to b.
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| 10 | | Return old bank select value.
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| 11 |
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| 12 |
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| 13 | | vfwait()
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| 14 |
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| 15 | | Wait for a FRAMESTOP update to transpire.
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| 16 | | ------------------------------------------------------------------------------
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[f40a309] | 17 | .xdef _vbank
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| 18 | .xdef _vfwait
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[4f508e6] | 19 |
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[f40a309] | 20 | .xref _v_regs
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[4f508e6] | 21 |
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[f40a309] | 22 | .text
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[4f508e6] | 23 |
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| 24 | B = 8
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| 25 |
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| 26 | OLDB = d6
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| 27 | NEWB = d7
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| 28 |
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| 29 | VSDD_R5 = 10
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| 30 | VSDD_R11 = 22
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| 31 |
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| 32 | VT_BASE = 128 | word offset of VSDD Access Table
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| 33 |
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| 34 | VT_1 = VT_BASE+300 | high time
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| 35 | VT_2 = VT_BASE+2 | low time
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| 36 |
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[f40a309] | 37 | .page
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[4f508e6] | 38 | | ------------------------------------------------------------------------------
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| 39 | | vbank(b) -- change VSDD Data Segment bank to b. Return old bank.
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| 40 | | Assumes a 128K byte window, sets S15..S11 to zero.
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| 41 | | ------------------------------------------------------------------------------
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| 42 |
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| 43 |
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| 44 | _vbank: link a6,#0 | link stack frames
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| 45 | movem.l d5-d7,-(sp) | preserve registers
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| 46 | move.w _v_regs+VSDD_R5,OLDB | get v_regs[5]
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| 47 | lsr.w #6,OLDB | extract BS bits
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| 48 | move.w OLDB,d0 | ...
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| 49 | andi.w #2,d0 | ...
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| 50 | move.w OLDB,d1 | ...
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| 51 | lsr.w #2,d1 | ...
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| 52 | andi.w #1,d1 | ...
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| 53 | or.w d1,d0 | ...
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| 54 | move.w d0,OLDB | ...
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| 55 | cmp.w B(a6),OLDB | see if they're what we want
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| 56 | bne L2 | jump if not
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| 57 |
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| 58 | move.w B(a6),d0 | setup to return b
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[f40a309] | 59 | bra L1
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[4f508e6] | 60 |
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| 61 | L2: move.w B(a6),NEWB | get bank bits from b
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| 62 | lsl.w #6,NEWB | shift bits from b into BS bits
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| 63 | move.w NEWB,d0 | ...
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| 64 | andi.w #128,d0 | ...
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| 65 | lsl.w #2,NEWB | ...
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| 66 | andi.w #256,NEWB | ...
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| 67 | or.w NEWB,d0 | ...
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| 68 | move.w d0,_v_regs+VSDD_R5 | set v_regs[5] with new BS bits
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| 69 |
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| 70 | vw1b: cmp.w #VT_1,_v_regs+VSDD_R11 | wait for FRAMESTOP
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| 71 | bcc vw1b | ...
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| 72 |
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| 73 | vw2b: cmp.w #VT_1,_v_regs+VSDD_R11 | ...
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| 74 | bcs vw2b | ...
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| 75 |
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| 76 | vw3b: cmp.w #VT_1,_v_regs+VSDD_R11 | ...
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| 77 | bcc vw3b | ...
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| 78 |
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| 79 | vw4b: cmp.w #VT_2,_v_regs+VSDD_R11 | ...
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| 80 | bcs vw4b | ...
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| 81 |
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| 82 | move.w OLDB,d0 | setup to return OLDB
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| 83 |
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| 84 | L1: tst.l (sp)+ | fixup stack
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| 85 | movem.l (sp)+,OLDB-NEWB | restore registers
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| 86 | unlk a6 | unlink stack frames
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| 87 | rts | return to caller
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| 88 |
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[f40a309] | 89 | .page
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[4f508e6] | 90 |
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| 91 | | ------------------------------------------------------------------------------
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| 92 | | vfwait() -- Wait for a FRAMESTOP update to transpire.
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| 93 | | ------------------------------------------------------------------------------
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| 94 |
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| 95 | _vfwait: link a6,#0 | link stack frames
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| 96 |
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| 97 | vw1a: cmp.w #VT_1,_v_regs+VSDD_R11 | wait for FRAMESTOP
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| 98 | bcc vw1a | ...
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| 99 |
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| 100 | vw2a: cmp.w #VT_1,_v_regs+VSDD_R11 | ...
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| 101 | bcs vw2a | ...
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| 102 |
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| 103 | vw3a: cmp.w #VT_1,_v_regs+VSDD_R11 | ...
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| 104 | bcc vw3a | ...
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| 105 |
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| 106 | vw4a: cmp.w #VT_2,_v_regs+VSDD_R11 | ...
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| 107 | bcs vw4a | ...
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| 108 |
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| 109 | unlk a6 | unlink stack frames
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| 110 | rts | return to caller
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| 111 |
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[f40a309] | 112 | .end
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