| 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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