[90] | 1 | ; Project name : XTIDE Universal BIOS |
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[3] | 2 | ; Description : Int 19h BIOS functions (Boot Strap Loader). |
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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 | B_READ_RETRY_TIMES EQU 3 ; Number of times to retry |
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| 8 | |
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| 9 | |
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| 10 | ;-------------------------------------------------------------------- |
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| 11 | ; Boots if boot sector is successfully read from the drive. |
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| 12 | ; |
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| 13 | ; Int19h_TryToLoadBootSectorFromDL |
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| 14 | ; Parameters: |
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| 15 | ; DL: Drive to boot from (translated, 00h or 80h) |
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| 16 | ; DS: RAMVARS segment |
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| 17 | ; Returns: |
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| 18 | ; ES:BX: Ptr to boot sector (if successfull) |
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| 19 | ; CF: Set if boot sector loaded succesfully |
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| 20 | ; Cleared if failed to load boot sector |
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| 21 | ; Corrupts registers: |
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| 22 | ; AX, CX, DH, DI, (DL if failed to read boot sector) |
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| 23 | ;-------------------------------------------------------------------- |
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| 24 | ALIGN JUMP_ALIGN |
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| 25 | Int19h_TryToLoadBootSectorFromDL: |
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| 26 | call BootPrint_TryToBootFromDL |
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[95] | 27 | call LoadFirstSectorFromDriveDL |
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[3] | 28 | jc SHORT .FailedToLoadFirstSector |
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[61] | 29 | |
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| 30 | test dl, 80h |
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| 31 | jz SHORT .AlwaysBootFromFloppyDriveForBooterGames |
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[3] | 32 | cmp WORD [es:bx+510], 0AA55h ; Valid boot sector? |
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[61] | 33 | jne SHORT .FirstHardDiskSectorNotBootable |
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| 34 | .AlwaysBootFromFloppyDriveForBooterGames: |
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[95] | 35 | mov bx, g_szFound |
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| 36 | call BootPrint_BootSectorResultStringFromBX |
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[3] | 37 | stc |
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| 38 | ret |
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| 39 | .FailedToLoadFirstSector: |
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| 40 | call BootPrint_FailedToLoadFirstSector |
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| 41 | clc |
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| 42 | ret |
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[61] | 43 | .FirstHardDiskSectorNotBootable: |
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[95] | 44 | mov bx, g_szNotFound |
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| 45 | call BootPrint_BootSectorResultStringFromBX |
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[3] | 46 | clc |
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| 47 | ret |
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| 48 | |
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| 49 | ;-------------------------------------------------------------------- |
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[95] | 50 | ; LoadFirstSectorFromDriveDL |
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[3] | 51 | ; Parameters: |
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| 52 | ; DL: Drive to boot from (translated, 00h or 80h) |
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| 53 | ; Returns: |
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| 54 | ; AH: INT 13h error code |
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| 55 | ; ES:BX: Ptr to boot sector (if successfull) |
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| 56 | ; CF: Cleared if read successfull |
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| 57 | ; Set if any error |
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| 58 | ; Corrupts registers: |
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| 59 | ; AL, CX, DH, DI |
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| 60 | ;-------------------------------------------------------------------- |
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| 61 | ALIGN JUMP_ALIGN |
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[95] | 62 | LoadFirstSectorFromDriveDL: |
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[3] | 63 | LOAD_BDA_SEGMENT_TO es, bx ; ES:BX now points to... |
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| 64 | mov bx, BOOTVARS.rgbBootSect ; ...boot sector location |
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[95] | 65 | mov di, B_READ_RETRY_TIMES ; Initialize retry counter |
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[3] | 66 | ALIGN JUMP_ALIGN |
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| 67 | .ReadRetryLoop: |
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[28] | 68 | call .ResetBootDriveFromDL |
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| 69 | call .LoadFirstSectorFromDLtoESBX |
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[3] | 70 | jnc SHORT .Return |
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| 71 | dec di ; Decrement retry counter |
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| 72 | jnz SHORT .ReadRetryLoop ; Loop while retries left |
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| 73 | ALIGN JUMP_ALIGN |
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| 74 | .Return: |
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| 75 | ret |
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| 76 | |
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| 77 | ;-------------------------------------------------------------------- |
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[28] | 78 | ; .ResetBootDriveFromDL |
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[3] | 79 | ; Parameters: |
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| 80 | ; DL: Drive to boot from (translated, 00h or 80h) |
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| 81 | ; Returns: |
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| 82 | ; AH: INT 13h error code |
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| 83 | ; CF: Cleared if read successfull |
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| 84 | ; Set if any error |
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| 85 | ; Corrupts registers: |
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[28] | 86 | ; AL |
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[3] | 87 | ;-------------------------------------------------------------------- |
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| 88 | ALIGN JUMP_ALIGN |
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[28] | 89 | .ResetBootDriveFromDL: |
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| 90 | xor ax, ax ; AH=0h, Disk Controller Reset |
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| 91 | test dl, 80h ; Floppy drive? |
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[95] | 92 | eCMOVNZ ah, 0Dh ; AH=Dh, Reset Hard Disk (Alternate reset) |
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[3] | 93 | int INTV_DISK_FUNC |
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| 94 | ret |
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| 95 | |
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| 96 | ;-------------------------------------------------------------------- |
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[28] | 97 | ; Reads first sector (boot sector) from drive DL to ES:BX. |
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[3] | 98 | ; |
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[28] | 99 | ; .LoadFirstSectorFromDLtoESBX |
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[3] | 100 | ; Parameters: |
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| 101 | ; DL: Drive to boot from (translated, 00h or 80h) |
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[28] | 102 | ; ES:BX: Destination buffer for boot sector |
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[3] | 103 | ; Returns: |
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[28] | 104 | ; AH: INT 13h error code |
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| 105 | ; ES:BX: Ptr to boot sector |
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| 106 | ; CF: Cleared if read successfull |
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| 107 | ; Set if any error |
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[3] | 108 | ; Corrupts registers: |
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[28] | 109 | ; AL, CX, DH |
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[3] | 110 | ;-------------------------------------------------------------------- |
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| 111 | ALIGN JUMP_ALIGN |
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[28] | 112 | .LoadFirstSectorFromDLtoESBX: |
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| 113 | mov ax, 0201h ; Read 1 sector |
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| 114 | mov cx, 1 ; Cylinder 0, Sector 1 |
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| 115 | xor dh, dh ; Head 0 |
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[3] | 116 | int INTV_DISK_FUNC |
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| 117 | ret |
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| 118 | |
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| 119 | |
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| 120 | ;-------------------------------------------------------------------- |
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| 121 | ; Jumps to boot sector pointed by ES:BX. |
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| 122 | ; |
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| 123 | ; Int19h_JumpToBootSector |
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| 124 | ; Parameters: |
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| 125 | ; DL: Drive to boot from (translated, 00h or 80h) |
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| 126 | ; ES:BX: Ptr to boot sector |
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| 127 | ; Returns: |
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| 128 | ; Never returns |
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| 129 | ;-------------------------------------------------------------------- |
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| 130 | ALIGN JUMP_ALIGN |
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| 131 | Int19h_JumpToBootSector: |
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| 132 | push es ; Push boot sector segment |
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| 133 | push bx ; Push boot sector offset |
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| 134 | call Int19h_ClearSegmentsForBoot |
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| 135 | xor dh, dh ; Device supported by INT 13h |
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| 136 | retf |
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| 137 | |
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| 138 | ;-------------------------------------------------------------------- |
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| 139 | ; Clears DS and ES registers to zero. |
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| 140 | ; |
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| 141 | ; Int19h_ClearSegmentsForBoot |
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| 142 | ; Parameters: |
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| 143 | ; Nothing |
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| 144 | ; Returns: |
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| 145 | ; DS=ES: Zero |
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| 146 | ; Corrupts registers: |
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| 147 | ; AX |
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| 148 | ;-------------------------------------------------------------------- |
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| 149 | ALIGN JUMP_ALIGN |
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| 150 | Int19h_ClearSegmentsForBoot: |
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| 151 | xor ax, ax |
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| 152 | mov ds, ax |
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| 153 | mov es, ax |
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| 154 | ret |
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