| [48] | 1 | ; Project name : Assembly Library
|
|---|
| 2 | ; Description : Functions for preventing CGA snow.
|
|---|
| 3 |
|
|---|
| 4 | ; Section containing code
|
|---|
| 5 | SECTION .text
|
|---|
| 6 |
|
|---|
| [50] | 7 | ;--------------------------------------------------------------------
|
|---|
| 8 | ; CgaSnow_IsCgaPresent
|
|---|
| 9 | ; Parameters:
|
|---|
| 10 | ; DS: BDA segment (zero)
|
|---|
| 11 | ; Returns:
|
|---|
| 12 | ; CF: Set if CGA detected
|
|---|
| 13 | ; Cleared if CGA not detected
|
|---|
| 14 | ; Corrupts registers:
|
|---|
| 15 | ; AX
|
|---|
| 16 | ;--------------------------------------------------------------------
|
|---|
| 17 | ALIGN JUMP_ALIGN
|
|---|
| 18 | CgaSnow_IsCgaPresent:
|
|---|
| 19 | cmp WORD [BDA.wVidPort], CGA_STATUS_REGISTER - OFFSET_TO_CGA_STATUS_REGISTER
|
|---|
| 20 | jne SHORT .CgaNotFound
|
|---|
| [52] | 21 |
|
|---|
| 22 | ; All standard CGA modes use 25 rows but only EGA and later store it to BDA.
|
|---|
| 23 | cmp BYTE [BDA.bVidRows], 25
|
|---|
| 24 | jge SHORT .CgaNotFound
|
|---|
| [50] | 25 | stc
|
|---|
| 26 | ret
|
|---|
| 27 | ALIGN JUMP_ALIGN
|
|---|
| 28 | .CgaNotFound:
|
|---|
| 29 | clc
|
|---|
| 30 | ret
|
|---|
| [48] | 31 |
|
|---|
| [50] | 32 |
|
|---|
| [162] | 33 | ; CGA snow prevention must be kept optional to avoid unnecessary
|
|---|
| 34 | ; overhead when building programs meant for non-CGA systems.
|
|---|
| [48] | 35 | %ifdef ELIMINATE_CGA_SNOW
|
|---|
| 36 |
|
|---|
| 37 | ;--------------------------------------------------------------------
|
|---|
| [49] | 38 | ; CgaSnow_Stosb
|
|---|
| 39 | ; CgaSnow_Stosw
|
|---|
| [48] | 40 | ; Parameters:
|
|---|
| 41 | ; AL: Character to output
|
|---|
| 42 | ; AH: Attribute to output (CgaSnow_StoswWithoutCgaSnow only)
|
|---|
| 43 | ; DS: BDA segment (zero)
|
|---|
| 44 | ; ES:DI: Ptr to video memory where to output
|
|---|
| 45 | ; Returns:
|
|---|
| 46 | ; DI: Incremented for next character
|
|---|
| 47 | ; Corrupts registers:
|
|---|
| 48 | ; AX, DX
|
|---|
| 49 | ;--------------------------------------------------------------------
|
|---|
| 50 | ALIGN JUMP_ALIGN
|
|---|
| [49] | 51 | CgaSnow_Stosb:
|
|---|
| [50] | 52 | call LoadCgaStatusRegisterAddressToDXifCgaPresent
|
|---|
| 53 | jz SHORT .StosbWithoutWaitSinceUnknownPort
|
|---|
| [48] | 54 |
|
|---|
| 55 | mov ah, al
|
|---|
| 56 | cli ; Interrupt request would mess up timing
|
|---|
| 57 | WAIT_UNTIL_SAFE_CGA_WRITE
|
|---|
| 58 | mov al, ah
|
|---|
| 59 | .StosbWithoutWaitSinceUnknownPort:
|
|---|
| 60 | stosb
|
|---|
| 61 | sti
|
|---|
| 62 | ret
|
|---|
| 63 |
|
|---|
| 64 | ALIGN JUMP_ALIGN
|
|---|
| [49] | 65 | CgaSnow_Stosw:
|
|---|
| [48] | 66 | push bx
|
|---|
| [50] | 67 | call LoadCgaStatusRegisterAddressToDXifCgaPresent
|
|---|
| 68 | jz SHORT .StoswWithoutWaitSinceUnknownPort
|
|---|
| [48] | 69 |
|
|---|
| 70 | xchg bx, ax
|
|---|
| 71 | cli ; Interrupt request would mess up timing
|
|---|
| 72 | WAIT_UNTIL_SAFE_CGA_WRITE
|
|---|
| 73 | xchg ax, bx
|
|---|
| 74 | .StoswWithoutWaitSinceUnknownPort:
|
|---|
| 75 | stosw
|
|---|
| [162] | 76 | sti
|
|---|
| [48] | 77 | pop bx
|
|---|
| 78 | ret
|
|---|
| 79 |
|
|---|
| 80 |
|
|---|
| 81 | ;--------------------------------------------------------------------
|
|---|
| [49] | 82 | ; CgaSnow_RepMovsb
|
|---|
| [48] | 83 | ; Parameters:
|
|---|
| 84 | ; CX: Number of characters to copy
|
|---|
| 85 | ; DS: BDA segment (zero)
|
|---|
| 86 | ; ES:SI: Ptr to video memory where to read from
|
|---|
| 87 | ; ES:DI: Ptr to video memory where to write to
|
|---|
| 88 | ; Returns:
|
|---|
| 89 | ; SI, DI: Updated for next character
|
|---|
| 90 | ; Corrupts registers:
|
|---|
| 91 | ; AX, CX, DX
|
|---|
| 92 | ;--------------------------------------------------------------------
|
|---|
| 93 | ALIGN JUMP_ALIGN
|
|---|
| [49] | 94 | CgaSnow_RepMovsb:
|
|---|
| [50] | 95 | call LoadCgaStatusRegisterAddressToDXifCgaPresent
|
|---|
| 96 | jz SHORT .RepMovsbWithoutWaitSinceUnknownPort
|
|---|
| [48] | 97 |
|
|---|
| 98 | .MovsbNextByte:
|
|---|
| 99 | cli ; Interrupt request would mess up timing
|
|---|
| 100 | WAIT_UNTIL_SAFE_CGA_WRITE
|
|---|
| 101 | eSEG es
|
|---|
| 102 | movsb
|
|---|
| 103 | sti
|
|---|
| 104 | loop .MovsbNextByte
|
|---|
| 105 | ret
|
|---|
| 106 | .RepMovsbWithoutWaitSinceUnknownPort:
|
|---|
| 107 | eSEG_STR rep, es, movsb
|
|---|
| 108 | ret
|
|---|
| 109 |
|
|---|
| 110 |
|
|---|
| 111 | ;--------------------------------------------------------------------
|
|---|
| [50] | 112 | ; LoadCgaStatusRegisterAddressToDXifCgaPresent
|
|---|
| [48] | 113 | ; Parameters:
|
|---|
| 114 | ; DS: BDA segment (zero)
|
|---|
| 115 | ; Returns:
|
|---|
| 116 | ; DX: CGA Status Register Address
|
|---|
| [50] | 117 | ; ZF: Set if CGA not present
|
|---|
| 118 | ; Cleared if CGA present
|
|---|
| [48] | 119 | ; Corrupts registers:
|
|---|
| 120 | ; Nothing
|
|---|
| 121 | ;--------------------------------------------------------------------
|
|---|
| 122 | ALIGN JUMP_ALIGN
|
|---|
| [50] | 123 | LoadCgaStatusRegisterAddressToDXifCgaPresent:
|
|---|
| 124 | test BYTE [VIDEO_BDA.displayContext+DISPLAY_CONTEXT.bFlags], FLG_CONTEXT_CGA
|
|---|
| 125 | jz SHORT .NoCgaDetected
|
|---|
| 126 | mov dx, CGA_STATUS_REGISTER
|
|---|
| 127 | ALIGN JUMP_ALIGN, ret
|
|---|
| 128 | .NoCgaDetected:
|
|---|
| [48] | 129 | ret
|
|---|
| 130 |
|
|---|
| 131 |
|
|---|
| 132 | %endif ; ELIMINATE_CGA_SNOW
|
|---|
