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_Stosb |
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18 | ; CgaSnow_Stosw |
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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_Stosb: |
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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_Stosw: |
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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_Scasb |
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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_Scasb: |
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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 | mov al, ah |
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80 | .ScasbWithoutWaitSinceUnknownPort: |
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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_RepMovsb |
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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_RepMovsb: |
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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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