[99] | 1 | ; Project name : XTIDE Universal BIOS
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[3] | 2 | ; Description : Functions for accessing DPT data.
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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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[150] | 8 | ; AccessDPT_GetDriveSelectByteToAL
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| 9 | ; Parameters:
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| 10 | ; DS:DI: Ptr to Disk Parameter Table
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| 11 | ; Returns:
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| 12 | ; AL: Drive Select Byte
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| 13 | ; Corrupts registers:
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| 14 | ; Nothing
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| 15 | ;--------------------------------------------------------------------
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| 16 | ALIGN JUMP_ALIGN
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| 17 | AccessDPT_GetDriveSelectByteToAL:
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| 18 | mov al, [di+DPT.wFlags]
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| 19 | and al, FLG_DRVNHEAD_LBA | FLG_DRVNHEAD_DRV
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| 20 | or al, MASK_DRVNHEAD_SET ; Bits set to 1 for old drives
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| 21 | ret
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| 22 |
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| 23 |
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| 24 | ;--------------------------------------------------------------------
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| 25 | ; AccessDPT_GetDeviceControlByteToAL
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| 26 | ; Parameters:
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| 27 | ; DS:DI: Ptr to Disk Parameter Table
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| 28 | ; Returns:
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| 29 | ; AL: Device Control Byte
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| 30 | ; Corrupts registers:
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| 31 | ; Nothing
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| 32 | ;--------------------------------------------------------------------
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| 33 | ALIGN JUMP_ALIGN
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| 34 | AccessDPT_GetDeviceControlByteToAL:
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| 35 | xor al, al
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[158] | 36 | test BYTE [di+DPT.bFlagsLow], FLGL_DPT_ENABLE_IRQ
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[150] | 37 | jnz SHORT .EnableDeviceIrq
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| 38 | or al, FLG_DEVCONTROL_nIEN ; Disable IRQ
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| 39 | .EnableDeviceIrq:
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| 40 | ret
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| 41 |
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[227] | 42 |
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[150] | 43 | ;--------------------------------------------------------------------
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[227] | 44 | ; AccessDPT_GetLCHStoAXBLBH
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[3] | 45 | ; Parameters:
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| 46 | ; DS:DI: Ptr to Disk Parameter Table
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| 47 | ; Returns:
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[227] | 48 | ; AX: Number of L-CHS cylinders
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| 49 | ; BL: Number of L-CHS heads
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| 50 | ; BH: Number of L-CHS sectors per track
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[3] | 51 | ; Corrupts registers:
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[227] | 52 | ; CX, DX
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[3] | 53 | ;--------------------------------------------------------------------
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[227] | 54 | AccessDPT_GetLCHStoAXBLBH:
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| 55 | ; Return LBA-assisted CHS if LBA addressing used
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[173] | 56 | test BYTE [di+DPT.bFlagsLow], FLG_DRVNHEAD_LBA
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[227] | 57 | jz SHORT .ConvertPchsToLchs
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[173] | 58 |
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[227] | 59 | call AccessDPT_GetLbaSectorCountToBXDXAX
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[324] | 60 | call AccessDPT_ConvertSectorCountFromBXDXAXtoLbaAssistedCHSinDXAXBLBH
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[227] | 61 | test dx, dx
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| 62 | jnz SHORT .LimitAXtoMaxLCHScylinders
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| 63 | cmp ax, MAX_LCHS_CYLINDERS
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[230] | 64 | jb SHORT .returnLCHS
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[227] | 65 | .LimitAXtoMaxLCHScylinders:
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| 66 | mov ax, MAX_LCHS_CYLINDERS
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| 67 | .returnLCHS:
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| 68 | ret
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[173] | 69 |
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[227] | 70 | .ConvertPchsToLchs:
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| 71 | mov ax, [di+DPT.wPchsCylinders]
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| 72 | mov bx, [di+DPT.wPchsHeadsAndSectors]
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[230] | 73 | ; Fall to AccessDPT_ShiftPCHinAXBLtoLCH
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[227] | 74 |
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| 75 |
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| 76 | ;--------------------------------------------------------------------
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| 77 | ; AccessDPT_ShiftPCHinAXBLtoLCH
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[173] | 78 | ; Parameters:
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[227] | 79 | ; AX: P-CHS cylinders (1...16383)
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| 80 | ; BL: P-CHS heads (1...16)
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[173] | 81 | ; Returns:
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[227] | 82 | ; AX: Number of L-CHS cylinders (1...1024)
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| 83 | ; BL: Number of L-CHS heads (1...255)
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[230] | 84 | ; CX: Number of bits shifted (4 at most)
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[173] | 85 | ; Corrupts registers:
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| 86 | ; Nothing
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| 87 | ;--------------------------------------------------------------------
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[227] | 88 | AccessDPT_ShiftPCHinAXBLtoLCH:
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[173] | 89 | xor cx, cx
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| 90 | .ShiftLoop:
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[227] | 91 | cmp ax, MAX_LCHS_CYLINDERS ; Need to shift?
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[231] | 92 | jbe SHORT .Return ; If not, return
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[173] | 93 | inc cx ; Increment shift count
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[227] | 94 | shr ax, 1 ; Halve cylinders
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| 95 | shl bl, 1 ; Double heads
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[231] | 96 | jnz SHORT .ShiftLoop ; Falls through only on the last (4th) iteration and only if BL was 16 on entry
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| 97 | dec bl ; DOS doesn't support drives with 256 heads so we limit heads to 255
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| 98 | ; We can save a byte here by using DEC BX if we don't care about BH
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| 99 | .Return:
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[173] | 100 | ret
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| 101 |
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[227] | 102 |
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[173] | 103 | ;--------------------------------------------------------------------
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[230] | 104 | ; AccessDPT_GetLbaSectorCountToBXDXAX
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| 105 | ; Parameters:
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| 106 | ; DS:DI: Ptr to Disk Parameter Table
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| 107 | ; Returns:
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| 108 | ; BX:DX:AX: 48-bit sector count
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| 109 | ; Corrupts registers:
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| 110 | ; Nothing
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| 111 | ;--------------------------------------------------------------------
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| 112 | AccessDPT_GetLbaSectorCountToBXDXAX:
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| 113 | mov ax, [di+DPT.twLbaSectors]
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| 114 | mov dx, [di+DPT.twLbaSectors+2]
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| 115 | mov bx, [di+DPT.twLbaSectors+4]
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| 116 | ret
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| 117 |
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| 118 |
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| 119 | ;--------------------------------------------------------------------
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[3] | 120 | ; Returns pointer to DRVPARAMS for master or slave drive.
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| 121 | ;
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| 122 | ; AccessDPT_GetPointerToDRVPARAMStoCSBX
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| 123 | ; Parameters:
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| 124 | ; DS:DI: Ptr to Disk Parameter Table
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| 125 | ; Returns:
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| 126 | ; CS:BX: Ptr to DRVPARAMS
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| 127 | ; Corrupts registers:
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| 128 | ; Nothing
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| 129 | ;--------------------------------------------------------------------
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| 130 | ALIGN JUMP_ALIGN
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| 131 | AccessDPT_GetPointerToDRVPARAMStoCSBX:
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[150] | 132 | eMOVZX bx, [di+DPT.bIdevarsOffset] ; CS:BX points to IDEVARS
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| 133 | add bx, BYTE IDEVARS.drvParamsMaster ; CS:BX points to Master Drive DRVPARAMS
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[158] | 134 | test BYTE [di+DPT.bFlagsLow], FLGL_DPT_SLAVE
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[150] | 135 | jz SHORT .ReturnPointerToDRVPARAMS
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| 136 | add bx, BYTE DRVPARAMS_size ; CS:BX points to Slave Drive DRVPARAMS
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| 137 | .ReturnPointerToDRVPARAMS:
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[3] | 138 | ret
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[200] | 139 |
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| 140 | ;--------------------------------------------------------------------
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| 141 | ; AccessDPT_GetUnshiftedAddressModeToALZF
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| 142 | ; Parameters:
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| 143 | ; DS:DI: Ptr to Disk Parameter Table
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| 144 | ; Returns:
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[230] | 145 | ; AL: Addressing Mode (L-CHS, P-CHS, LBA28, LBA48)
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[200] | 146 | ; unshifted (still shifted where it is in bFlagsLow)
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| 147 | ; ZF: Set based on value in AL
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| 148 | ; Corrupts registers:
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| 149 | ; AL
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| 150 | ;--------------------------------------------------------------------
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[230] | 151 | ;
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| 152 | ; Converted to a macro since only called in two places, and the call/ret overhead
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[200] | 153 | ; is not worth it for these two instructions (4 bytes total)
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| 154 | ;
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| 155 | %macro AccessDPT_GetUnshiftedAddressModeToALZF 0
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| 156 | mov al, [di+DPT.bFlagsLow]
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| 157 | and al, MASKL_DPT_ADDRESSING_MODE
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| 158 | %endmacro
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[324] | 159 |
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| 160 |
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| 161 | ;--------------------------------------------------------------------
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| 162 | ; LBA assist calculation:
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| 163 | ; this is how to fit a big drive into INT13's skimpy size requirements,
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| 164 | ; with a maximum of 8.4G available.
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| 165 | ;
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| 166 | ; total LBAs (as obtained by words 60+61)
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| 167 | ; divided by 63 (sectors per track) (save as value A)
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| 168 | ; Sub 1 from A
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| 169 | ; divide A by 1024 + truncate.
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| 170 | ; == total number of heads to use.
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| 171 | ; add 1
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| 172 | ; this value must be either 16, 32, 64, 128, or 256 (round up)
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| 173 | ; then take the value A above and divide by # of heads
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| 174 | ; to get the # of cylinders to use.
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| 175 | ;
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| 176 | ;
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| 177 | ; so a LBA28 drive will have 268,435,456 as maximum LBAs
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| 178 | ;
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| 179 | ; 10000000h / 63 = 410410h (total cylinders or tracks)
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| 180 | ; 410410h / 1024 = 1041h, which is way more than 256 heads, but 256 is max.
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| 181 | ; 410410h / 256 = 4104h cylinders
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| 182 | ;
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| 183 | ; there's a wealth of information at: http://www.mossywell.com/boot-sequence
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| 184 | ; they show a slightly different approach to LBA assist calulations, but
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| 185 | ; the method here provides compatibility with phoenix BIOS
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| 186 | ;
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| 187 | ; we're using the values from 60+61 here because we're topping out at 8.4G
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| 188 | ; anyway, so there's no need to use the 48bit LBA values.
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| 189 | ;
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| 190 | ; AccessDPT_ConvertSectorCountFromBXDXAXtoLbaAssistedCHStoDXAXBLBH:
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| 191 | ; Parameters:
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| 192 | ; BX:DX:AX: Total number of sectors
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| 193 | ; Returns:
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| 194 | ; DX:AX: Number of cylinders
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| 195 | ; BH: Number of sectors per track (always 63)
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| 196 | ; BL: Number of heads (16, 32, 64, 128 or 255)
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| 197 | ; Corrupts registers:
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| 198 | ; CX
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| 199 | ;--------------------------------------------------------------------
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| 200 | AccessDPT_ConvertSectorCountFromBXDXAXtoLbaAssistedCHSinDXAXBLBH:
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| 201 | push bp
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| 202 | push si
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| 203 |
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| 204 | ; Value A = Total sector count / 63
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| 205 | xor cx, cx
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| 206 | push cx ; Push zero for bits 48...63
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| 207 | push bx
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| 208 | push dx
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| 209 | push ax ; 64-bit sector count now in stack
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| 210 | mov cl, LBA_ASSIST_SPT
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| 211 | mov bp, sp ; SS:BP now points sector count
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| 212 | call Math_DivQWatSSBPbyCX ; Temporary value A now in stack
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| 213 |
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| 214 | ; BX = Number of heads = A / 1024
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| 215 | mov ax, [bp]
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| 216 | mov dx, [bp+2]
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| 217 | mov bx, [bp+4]
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| 218 | call Size_DivideSizeInBXDXAXby1024andIncrementMagnitudeInCX
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| 219 |
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| 220 | ; Heads must be 16, 32, 64, 128 or 256 (round up)
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| 221 | mov bx, 256 ; Max number of heads
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| 222 | test dx, dx ; 65536 or more heads?
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| 223 | jnz SHORT .GetNumberOfCylinders
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| 224 | mov cx, 128 ; Half BX for rounding up
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| 225 | .FindMostSignificantBitForHeadSize:
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| 226 | cmp ax, cx
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| 227 | jae SHORT .GetNumberOfCylinders
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| 228 | shr cx, 1
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| 229 | shr bx, 1 ; Halve number of heads
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| 230 | jmp SHORT .FindMostSignificantBitForHeadSize
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| 231 |
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| 232 | ; DX:AX = Number of cylinders = A / number of heads
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| 233 | .GetNumberOfCylinders:
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| 234 | mov cx, bx
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| 235 | call Math_DivQWatSSBPbyCX
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| 236 | mov ax, [bp]
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| 237 | mov dx, [bp+2] ; Cylinders now in DX:AX
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| 238 |
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| 239 | ; Return LBA assisted CHS
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| 240 | add sp, BYTE 8 ; Clean stack
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| 241 | sub bl, bh ; Limit heads to 255
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| 242 | mov bh, LBA_ASSIST_SPT
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| 243 | pop si
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| 244 | pop bp
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| 245 | ret
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