2019-03-25 09:51:37 +01:00
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org 0x7C00
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bpb:
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jmp _startup ; 2 bytes
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nop ; 1 byte
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.oem:
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2019-03-25 23:00:07 +01:00
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db "OEM " ; OEM
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2019-03-25 09:51:37 +01:00
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.bps:
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dw 0x200 ; bytes per sector
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.spc:
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db 1 ; sectors per cluster
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.rsectors:
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dw 2 ; number of reserved sectors
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2019-03-25 23:00:07 +01:00
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.fats:
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2019-03-25 09:51:37 +01:00
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db 2 ; number of file allocation tables
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.dirents:
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dw 2 ; Number of directory entries
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2019-03-25 23:00:07 +01:00
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.sectors:
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2019-03-25 09:51:37 +01:00
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dw 720 ; total number of sectors
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.mtd: ; media descriptor type
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db 0xFD ; 5.25-inch Double sided, 40 tracks per side, 9 sectors per track (360 KB)
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.spfat: ; sectors per fat
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dw 0
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.spt:
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dw 9 ; sectors per track
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2019-03-25 23:00:07 +01:00
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.heads:
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2019-03-25 09:51:37 +01:00
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dw 2 ; number of heads
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2019-03-25 23:00:07 +01:00
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.hidsecs:
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2019-03-25 09:51:37 +01:00
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dd 0 ; number of hidden sectors
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2019-03-25 23:00:07 +01:00
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.lrgsectors:
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2019-03-25 09:51:37 +01:00
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dd 0 ; large sector count
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times (0x3E - ($-$$)) nop
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_startup:
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2019-03-25 23:00:07 +01:00
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call printgeo
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2019-03-25 09:51:37 +01:00
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mov ah, 0x08
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mov dl, 0x00
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2019-03-25 23:00:07 +01:00
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int 0x13 ; required, QEMU detects 360kB as 1200kB with CHS 80 2 15
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jc .noadjust
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inc dh
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mov [bpb.heads], dh
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2019-03-25 09:51:37 +01:00
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mov ax, cx
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and ax, 0x003F
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2019-03-25 23:00:07 +01:00
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mov [bpb.spt], ax ; no adjustment because sectors are 1-indexed
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mov ax, cx
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xchg al, ah
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mov cl,6
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shr ah,cl
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inc ax ; convert from maximum number (0-based) to total number (1-based) of cylinders
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mul word [bpb.heads] ; number of tracks = number of cylinders * heads
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mul word [bpb.spt] ; number of sectors = number of tracks * sectors per track
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mov [bpb.sectors], ax
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.noadjust:
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call printgeo
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2019-03-25 09:51:37 +01:00
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.end:
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hlt
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jmp .end
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2019-03-25 23:00:07 +01:00
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printgeo:
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mov ax, [bpb.heads]
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call print16
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mov ax, [bpb.spt]
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call print16
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mov ax, [bpb.sectors]
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call print16
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mov al, 0x0A
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call printc
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mov al, 0x0D
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call printc
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ret
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; in bx sector number,
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; dl drive number
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; ds:di buffer
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; out al error code,
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; carry set if error
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loadblk:
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mov ax, bx
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div byte [bpb.spt]
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call print16
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; Temp = LBA / (Sectors per Track)
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; Sector = (LBA % (Sectors per Track)) + 1
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; Head = Temp % (Number of Heads)
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; Cylinder = Temp / (Number of Heads)
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ret
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2019-03-25 09:51:37 +01:00
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%include "print.asm"
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times (0x1FE - ($-$$)) nop
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dw 0xAA55
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