122 lines
4.0 KiB
PHP
122 lines
4.0 KiB
PHP
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;*******************************************************
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;
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; Floppy16.inc
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; Floppy drive interface routines
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;
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; OS Development Series
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;*******************************************************
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%ifndef __FLOPPY16_INC_67343546FDCC56AAB872_INCLUDED__
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%define __FLOPPY16_INC_67343546FDCC56AAB872_INCLUDED__
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bits 16
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bpbOEM db "My OS "
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bpbBytesPerSector: DW 512
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bpbSectorsPerCluster: DB 1
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bpbReservedSectors: DW 1
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bpbNumberOfFATs: DB 2
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bpbRootEntries: DW 224
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bpbTotalSectors: DW 2880
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bpbMedia: DB 0xf0 ;; 0xF1
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bpbSectorsPerFAT: DW 9
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bpbSectorsPerTrack: DW 18
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bpbHeadsPerCylinder: DW 2
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bpbHiddenSectors: DD 0
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bpbTotalSectorsBig: DD 0
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bsDriveNumber: DB 0
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bsUnused: DB 0
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bsExtBootSignature: DB 0x29
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bsSerialNumber: DD 0xa0a1a2a3
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bsVolumeLabel: DB "MOS FLOPPY "
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bsFileSystem: DB "FAT12 "
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datasector dw 0x0000
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cluster dw 0x0000
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absoluteSector db 0x00
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absoluteHead db 0x00
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absoluteTrack db 0x00
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;************************************************;
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; Convert CHS to LBA
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; LBA = (cluster - 2) * sectors per cluster
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;************************************************;
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ClusterLBA:
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sub ax, 0x0002 ; zero base cluster number
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xor cx, cx
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mov cl, BYTE [bpbSectorsPerCluster] ; convert byte to word
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mul cx
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add ax, WORD [datasector] ; base data sector
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ret
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;************************************************;
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; Convert LBA to CHS
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; AX=>LBA Address to convert
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;
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; absolute sector = (logical sector / sectors per track) + 1
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; absolute head = (logical sector / sectors per track) MOD number of heads
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; absolute track = logical sector / (sectors per track * number of heads)
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;
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;************************************************;
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LBACHS:
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xor dx, dx ; prepare dx:ax for operation
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div WORD [bpbSectorsPerTrack] ; calculate
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inc dl ; adjust for sector 0
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mov BYTE [absoluteSector], dl
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xor dx, dx ; prepare dx:ax for operation
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div WORD [bpbHeadsPerCylinder] ; calculate
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mov BYTE [absoluteHead], dl
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mov BYTE [absoluteTrack], al
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ret
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;************************************************;
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; Reads a series of sectors
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; CX=>Number of sectors to read
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; AX=>Starting sector
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; ES:EBX=>Buffer to read to
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;************************************************;
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ReadSectors:
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.MAIN:
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mov di, 0x0005 ; five retries for error
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.SECTORLOOP:
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push ax
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push bx
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push cx
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call LBACHS ; convert starting sector to CHS
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mov ah, 0x02 ; BIOS read sector
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mov al, 0x01 ; read one sector
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mov ch, BYTE [absoluteTrack] ; track
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mov cl, BYTE [absoluteSector] ; sector
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mov dh, BYTE [absoluteHead] ; head
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mov dl, BYTE [bsDriveNumber] ; drive
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int 0x13 ; invoke BIOS
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jnc .SUCCESS ; test for read error
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xor ax, ax ; BIOS reset disk
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int 0x13 ; invoke BIOS
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dec di ; decrement error counter
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pop cx
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pop bx
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pop ax
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jnz .SECTORLOOP ; attempt to read again
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int 0x18
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.SUCCESS:
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pop cx
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pop bx
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pop ax
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add bx, WORD [bpbBytesPerSector] ; queue next buffer
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inc ax ; queue next sector
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loop .MAIN ; read next sector
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ret
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%endif ;__FLOPPY16_INC_67343546FDCC56AAB872_INCLUDED__
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