| 1 | ; File name : CgaSnow.asm
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| 2 | ; Project name : Assembly Library
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| 3 | ; Created date : 8.10.2010
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| 4 | ; Last update : 8.10.2010
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| 5 | ; Author : Tomi Tilli
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| 6 | ; Description : Functions for preventing CGA snow.
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| 7 |
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| 8 | ; Section containing code
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| 9 | SECTION .text
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| 10 |
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| 11 |
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| 12 | ; CGA snow preventing must be kept optional so unnecerrasy overhead
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| 13 | ; can be prevented when building program ment for non-CGA systems.
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| 14 | %ifdef ELIMINATE_CGA_SNOW
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| 15 |
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| 16 | ;--------------------------------------------------------------------
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| 17 | ; CgaSnow_StosbWithoutCgaSnow
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| 18 | ; CgaSnow_StoswWithoutCgaSnow
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| 19 | ; Parameters:
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| 20 | ; AL: Character to output
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| 21 | ; AH: Attribute to output (CgaSnow_StoswWithoutCgaSnow only)
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| 22 | ; DS: BDA segment (zero)
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| 23 | ; ES:DI: Ptr to video memory where to output
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| 24 | ; Returns:
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| 25 | ; DI: Incremented for next character
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| 26 | ; Corrupts registers:
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| 27 | ; AX, DX
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| 28 | ;--------------------------------------------------------------------
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| 29 | ALIGN JUMP_ALIGN
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| 30 | CgaSnow_StosbWithoutCgaSnow:
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| 31 | call LoadAndVerifyStatusRegisterFromBDA
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| 32 | jne SHORT .StosbWithoutWaitSinceUnknownPort
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| 33 |
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| 34 | mov ah, al
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| 35 | cli ; Interrupt request would mess up timing
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| 36 | WAIT_UNTIL_SAFE_CGA_WRITE
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| 37 | mov al, ah
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| 38 | .StosbWithoutWaitSinceUnknownPort:
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| 39 | stosb
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| 40 | sti
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| 41 | ret
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| 42 |
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| 43 | ALIGN JUMP_ALIGN
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| 44 | CgaSnow_StoswWithoutCgaSnow:
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| 45 | push bx
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| 46 | call LoadAndVerifyStatusRegisterFromBDA
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| 47 | jne SHORT .StoswWithoutWaitSinceUnknownPort
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| 48 |
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| 49 | xchg bx, ax
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| 50 | cli ; Interrupt request would mess up timing
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| 51 | WAIT_UNTIL_SAFE_CGA_WRITE
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| 52 | xchg ax, bx
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| 53 | .StoswWithoutWaitSinceUnknownPort:
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| 54 | stosw
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| 55 | pop bx
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| 56 | sti
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| 57 | ret
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| 58 |
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| 59 |
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| 60 | ;--------------------------------------------------------------------
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| 61 | ; CgaSnow_ScasbWithoutCgaSnow
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| 62 | ; Parameters:
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| 63 | ; AL: Byte for comparison
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| 64 | ; DS: BDA segment (zero)
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| 65 | ; ES:DI: Ptr to video memory where to output
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| 66 | ; Returns:
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| 67 | ; DI: Incremented for next character
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| 68 | ; Corrupts registers:
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| 69 | ; AX, DX
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| 70 | ;--------------------------------------------------------------------
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| 71 | ALIGN JUMP_ALIGN
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| 72 | CgaSnow_ScasbWithoutCgaSnow:
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| 73 | call LoadAndVerifyStatusRegisterFromBDA
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| 74 | jne SHORT .ScasbWithoutWaitSinceUnknownPort
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| 75 |
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| 76 | mov ah, al
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| 77 | cli ; Interrupt request would mess up timing
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| 78 | WAIT_UNTIL_SAFE_CGA_WRITE
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| 79 | .ScasbWithoutWaitSinceUnknownPort:
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| 80 | mov al, ah
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| 81 | scasb
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| 82 | sti
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| 83 | ret
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| 84 |
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| 85 |
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| 86 | ;--------------------------------------------------------------------
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| 87 | ; CgaSnow_RepMovsbWithoutCgaSnow
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| 88 | ; Parameters:
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| 89 | ; CX: Number of characters to copy
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| 90 | ; DS: BDA segment (zero)
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| 91 | ; ES:SI: Ptr to video memory where to read from
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| 92 | ; ES:DI: Ptr to video memory where to write to
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| 93 | ; Returns:
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| 94 | ; SI, DI: Updated for next character
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| 95 | ; Corrupts registers:
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| 96 | ; AX, CX, DX
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| 97 | ;--------------------------------------------------------------------
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| 98 | ALIGN JUMP_ALIGN
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| 99 | CgaSnow_RepMovsbWithoutCgaSnow:
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| 100 | call LoadAndVerifyStatusRegisterFromBDA
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| 101 | jne SHORT .RepMovsbWithoutWaitSinceUnknownPort
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| 102 |
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| 103 | .MovsbNextByte:
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| 104 | cli ; Interrupt request would mess up timing
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| 105 | WAIT_UNTIL_SAFE_CGA_WRITE
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| 106 | eSEG es
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| 107 | movsb
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| 108 | sti
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| 109 | loop .MovsbNextByte
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| 110 | ret
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| 111 | .RepMovsbWithoutWaitSinceUnknownPort:
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| 112 | eSEG_STR rep, es, movsb
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| 113 | ret
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| 114 |
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| 115 |
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| 116 | ;--------------------------------------------------------------------
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| 117 | ; LoadAndVerifyStatusRegisterFromBDA
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| 118 | ; Parameters:
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| 119 | ; DS: BDA segment (zero)
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| 120 | ; Returns:
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| 121 | ; DX: CGA Status Register Address
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| 122 | ; ZF: Set if CGA Base Port found in BDA
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| 123 | ; Corrupts registers:
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| 124 | ; Nothing
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| 125 | ;--------------------------------------------------------------------
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| 126 | ALIGN JUMP_ALIGN
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| 127 | LoadAndVerifyStatusRegisterFromBDA:
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| 128 | mov dx, [BDA.wVidPort]
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| 129 | add dl, OFFSET_TO_CGA_STATUS_REGISTER
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| 130 | cmp dx, CGA_STATUS_REGISTER
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| 131 | je SHORT .CheckIfEgaOrLater
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| 132 | ret
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| 133 |
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| 134 | ALIGN JUMP_ALIGN
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| 135 | .CheckIfEgaOrLater:
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| 136 | push ax
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| 137 | call DisplayPage_GetColumnsToALandRowsToAH
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| 138 | cmp ah, [BDA.bVidRows] ; Video rows stored only by EGA and later
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| 139 | lahf
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| 140 | xor ah, 1<<6 ; Invert ZF
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| 141 | sahf
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| 142 | pop ax
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| 143 | ret
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| 144 |
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| 145 |
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| 146 | %endif ; ELIMINATE_CGA_SNOW
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