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