| 1 | ; Project name : Assembly Library
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| 2 | ; Description : Functions for preventing CGA snow.
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| 3 |
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| 4 | ; Section containing code
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| 5 | SECTION .text
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| 6 |
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| 7 | ;--------------------------------------------------------------------
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| 8 | ; CgaSnow_IsCgaPresent
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| 9 | ; Parameters:
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| 10 | ; DS: BDA segment (zero)
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| 11 | ; Returns:
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| 12 | ; CF: Set if CGA detected
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| 13 | ; Cleared if CGA not detected
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| 14 | ; Corrupts registers:
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| 15 | ; AX
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| 16 | ;--------------------------------------------------------------------
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| 17 | ALIGN JUMP_ALIGN
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| 18 | CgaSnow_IsCgaPresent:
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| 19 | cmp WORD [BDA.wVidPort], CGA_STATUS_REGISTER - OFFSET_TO_CGA_STATUS_REGISTER
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| 20 | jne SHORT .CgaNotFound
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| 21 |
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| 22 | ; All standard CGA modes use 25 rows but only EGA and later store it to BDA.
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| 23 | cmp BYTE [BDA.bVidRows], 25
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| 24 | jge SHORT .CgaNotFound
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| 25 | stc
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| 26 | ret
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| 27 | ALIGN JUMP_ALIGN
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| 28 | .CgaNotFound:
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| 29 | clc
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| 30 | ret
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| 31 |
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| 32 |
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| 33 | ; CGA snow prevention must be kept optional to avoid unnecessary
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| 34 | ; overhead when building programs meant for non-CGA systems.
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| 35 | %ifdef ELIMINATE_CGA_SNOW
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| 36 |
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| 37 | ;--------------------------------------------------------------------
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| 38 | ; CgaSnow_Stosb
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| 39 | ; CgaSnow_Stosw
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| 40 | ; Parameters:
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| 41 | ; AL: Character to output
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| 42 | ; AH: Attribute to output (CgaSnow_StoswWithoutCgaSnow only)
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| 43 | ; DS: BDA segment (zero)
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| 44 | ; ES:DI: Ptr to video memory where to output
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| 45 | ; Returns:
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| 46 | ; DI: Incremented for next character
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| 47 | ; Corrupts registers:
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| 48 | ; AX, DX
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| 49 | ;--------------------------------------------------------------------
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| 50 | ALIGN JUMP_ALIGN
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| 51 | CgaSnow_Stosb:
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| 52 | call LoadCgaStatusRegisterAddressToDXifCgaPresent
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| 53 | jz SHORT .StosbWithoutWaitSinceUnknownPort
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| 54 |
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| 55 | mov ah, al
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| 56 | cli ; Interrupt request would mess up timing
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| 57 | WAIT_UNTIL_SAFE_CGA_WRITE
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| 58 | mov al, ah
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| 59 | .StosbWithoutWaitSinceUnknownPort:
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| 60 | stosb
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| 61 | sti
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| 62 | ret
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| 63 |
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| 64 | ALIGN JUMP_ALIGN
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| 65 | CgaSnow_Stosw:
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| 66 | push bx
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| 67 | call LoadCgaStatusRegisterAddressToDXifCgaPresent
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| 68 | jz SHORT .StoswWithoutWaitSinceUnknownPort
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| 69 |
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| 70 | xchg bx, ax
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| 71 | cli ; Interrupt request would mess up timing
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| 72 | WAIT_UNTIL_SAFE_CGA_WRITE
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| 73 | xchg ax, bx
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| 74 | .StoswWithoutWaitSinceUnknownPort:
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| 75 | stosw
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| 76 | sti
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| 77 | pop bx
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| 78 | ret
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| 79 |
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| 80 |
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| 81 | ;--------------------------------------------------------------------
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| 82 | ; CgaSnow_RepMovsb
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| 83 | ; Parameters:
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| 84 | ; CX: Number of characters to copy
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| 85 | ; DS: BDA segment (zero)
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| 86 | ; ES:SI: Ptr to video memory where to read from
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| 87 | ; ES:DI: Ptr to video memory where to write to
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| 88 | ; Returns:
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| 89 | ; SI, DI: Updated for next character
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| 90 | ; Corrupts registers:
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| 91 | ; AX, CX, DX
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| 92 | ;--------------------------------------------------------------------
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| 93 | ALIGN JUMP_ALIGN
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| 94 | CgaSnow_RepMovsb:
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| 95 | call LoadCgaStatusRegisterAddressToDXifCgaPresent
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| 96 | jz SHORT .RepMovsbWithoutWaitSinceUnknownPort
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| 97 |
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| 98 | .MovsbNextByte:
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| 99 | cli ; Interrupt request would mess up timing
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| 100 | WAIT_UNTIL_SAFE_CGA_WRITE
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| 101 | es movsb
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| 102 | sti
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| 103 | loop .MovsbNextByte
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| 104 | ret
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| 105 | .RepMovsbWithoutWaitSinceUnknownPort:
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| 106 | eSEG_STR rep, es, movsb
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| 107 | ret
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| 108 |
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| 109 |
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| 110 | ;--------------------------------------------------------------------
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| 111 | ; LoadCgaStatusRegisterAddressToDXifCgaPresent
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| 112 | ; Parameters:
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| 113 | ; DS: BDA segment (zero)
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| 114 | ; Returns:
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| 115 | ; DX: CGA Status Register Address
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| 116 | ; ZF: Set if CGA not present
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| 117 | ; Cleared if CGA present
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| 118 | ; Corrupts registers:
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| 119 | ; Nothing
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| 120 | ;--------------------------------------------------------------------
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| 121 | ALIGN JUMP_ALIGN
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| 122 | LoadCgaStatusRegisterAddressToDXifCgaPresent:
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| 123 | test BYTE [VIDEO_BDA.displayContext+DISPLAY_CONTEXT.bFlags], FLG_CONTEXT_CGA
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| 124 | jz SHORT .NoCgaDetected
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| 125 | mov dx, CGA_STATUS_REGISTER
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| 126 | ALIGN JUMP_ALIGN, ret
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| 127 | .NoCgaDetected:
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| 128 | ret
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| 129 |
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| 130 |
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| 131 | %endif ; ELIMINATE_CGA_SNOW
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