576 lines
17 KiB
NASM
576 lines
17 KiB
NASM
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;++
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;
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;Module Name:
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;
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; fatnec98.asm
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;
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;Abstract:
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;
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; The ROM in NEC PC-9800 starts the boot process by performing a hardware
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; initialization and a verification of all external devices. If all goes
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; well, it will then load from the boot drive the sector from track 0, head 0,
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; sector 1. This sector is placed at physical address 1FC00h or 1FE00h.
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; This start address is decided by boot device.
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;
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; The code in this sector is responsible for locating NTLDR and
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; for placing the directory sector with this information at DirSeg:0.
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; After loading in this sector, it reads in the entirety of the BIOS at
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; BiosSeg:0 and does a long jump to the entry point at BiosSeg:0.
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;
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; There are no error message during execution of this code.
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; In case of NTLDR does not exist or BIOS read error, will sound beep.
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;
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; At the beginning of the boot sector, there is a table which describes the
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; structure of the media. This is equivalent to the BPB with some
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; additional information describing the physical layout of the driver (heads,
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; tracks, sectors)
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;
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;Author:
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;
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;
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;Environment:
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;
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; Real mode
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; FAT file system
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;
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;Revision History:
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;
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; 6/12/97 Tochizawa(NEC) support booting from 1.44MB FD
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;
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;--
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page ,132
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title boot - NTLDR FAT loader
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name fatboot
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.8086
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DIR_ENT struc
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Filename db 11 dup(?)
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Attribute db ?
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Reserved db 10 dup(?)
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Time dw 2 dup(?)
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StartCluster dw ?
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FileSize dd ?
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DIR_ENT ends
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;
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; This is the structure used to pass all shared data between the boot sector
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; and NTLDR.
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;
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SHARED struc
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ReadClusters dd ? ; function pointer
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ReadSectors dd ? ; function pointer
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SectorBase dd ? ; starting sector
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SHARED ends
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DoubleWord struc
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lsw dw ?
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msw dw ?
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DoubleWord ends
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SectorSize equ 512 ; sector size
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HiRes equ 00001000b
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DAFloppy equ 00010000b ; floppy bit in DA
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DASCSI equ 00100000b ; SCSI bit in DA
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SYS_PORT equ 37h
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BootSeg segment at 1fc0h
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BootSeg ends
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SysSeg segment at 0040h
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org 100h
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BIOS_FLAG label byte
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org 184h
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BootDrive98 label byte
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SysSeg ends
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DirSeg segment at 1000h
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DirSeg ends
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NtLdrSeg segment at 2000h
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NtLdrSeg ends
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BootCode segment ;would like to use BootSeg here, but LINK flips its lid
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ASSUME CS:BootCode,DS:NOTHING,ES:NOTHING,SS:NOTHING
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public FATBOOT
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FATBOOT proc far
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jmp short Start
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nop
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;
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; THE FOLLOWING DATA CONFIGURES THE BOOT PROGRAM
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; FOR ANY TYPE OF DRIVE OR HARDFILE
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;
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; Note that this data is just a place-holder here. The actual values will
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; be filled in by FORMAT or SYS. When installing the boot sector, only the
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; code following the BPB (from Start to the end) should be copied into the
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; first sector.
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;
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OsName db "MSWIN"
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OsVersion db "4.1"
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BPB label byte
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BytesPerSector dw SectorSize ; Size of a physical sector
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SectorsPerCluster db 8 ; Sectors per allocation unit
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ReservedSectors dw 4 ; Number of reserved sectors
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Fats db 2 ; Number of fats
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DirectoryEntries dw 0c00h ; Number of directory entries
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Sectors dw 0 ; No. of sectors - no. of hidden sectors
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Media db 0F8H ; Media byte
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FatSectors dw 70h ; Number of fat sectors
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SectorsPerTrack dw 23h ; Sectors per track
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Heads dw 7 ; Number of surfaces
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HiddenSectors dd 0f5h ; Number of hidden sectors
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SectorsLong dd 369c4h ; Number of sectors iff Sectors = 0
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;
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; The following byte is NOT part of the BPB but is set by SYS and format
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; We should NOT change its position.
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;
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; keep order of DriveNumber and CurrentHead!
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DriveNumber db 80h ; Physical drive number (0 or 80h)
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CurrentHead db 0 ; Unitialized
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Signature db 41 ; Signature Byte for bootsector
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BootID dd 0 ; Boot ID field.
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Boot_Vol_Label db "NO NAME "
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Boot_System_ID db 'FAT12 ' ;
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;
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; We need a shred data area with ntldr/setupldr.
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; But we don't have memory for using data area. Because bootcode size is 512KB.
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; There is nothing for it but to use this area.
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;
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NtldrSharedData label dword
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Start:
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assume DS:nothing,ES:nothing
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xor ax, ax ; Setup the stack to a known good spot
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mov ss, ax
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mov sp, 7c00h
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push cs
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pop ds
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assume DS:BootCode
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mov ax, SysSeg
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mov es, ax
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assume ES:SysSeg
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mov al, BootDrive98
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mov DriveNumber, al ; boot drive
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push si ; save partition info
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; We need some intialization.
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mov si, BytesPerSector ; keep it in reg
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test al, DAFloppy
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jnz Flg00
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; Boot is from hard disk.
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; Our BPB tells us BytesPerSector, but it is a logical value
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; that may differ from the physical value.
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; We need SectorShiftFactor that is used to convert logical sector address
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; to phisical sector address.
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mov ah, 84h ; ROM BIOS sense command
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xor bx, bx ; initialize bx to 0
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int 1Bh ;
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jc Flg01
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test bx, bx ; physical sector length returned ?
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jnz Flg02 ; if not,
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Flg01:
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mov bx, 256 ; we assume 256 bytes per sector
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Flg02:
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mov ax, si ; BytesPerSector
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xor dx, dx
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div bx
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mov NtldrSharedData.SectorShiftFactor, ax
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mov ax, 32*1024 ; 32KB
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; xor dx, dx ; dx must be 0 here.
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div si ; BytesPerSector
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mov NtldrSharedData.LogicalSectorsIn32KByte, al
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Flg00:
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; The system is now prepared for us to begin reading. First, determine
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; logical sector numbers of the start of the directory and the start of the
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; data area.
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;
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; We read all the directory entries into DirSeg.
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; It might be more than 64KB if hard disk.
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mov ax, size DIR_ENT
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mul DirectoryEntries ; (dx:ax) = # of bytes in directory
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dec si ; (si) = BytesPerSector -1
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add ax, si
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adc dx, 0
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inc si ; (si) = BytesPerSector
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div si ; (ax) = # of sectors in directory
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mov cx, ax ; save it in cx for later
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mov al, Fats
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xor ah, ah ; (ax) = # of FATs
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mul FatSectors ; (ax) = # of FAT sectors
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add ax, ReservedSectors ; (ax) = sector # directory starts
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adc dx, 0
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; save it in "Arguments" for later 'Read'
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mov NtldrSharedData.Arguments.SectorBase.lsw, ax
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mov NtldrSharedData.Arguments.SectorBase.msw, dx
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add ax, cx ; next sector after directory
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mov NtldrSharedData.ClusterBase, ax ; save it for later use
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Rpt00:
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push cx ; (cx) = # of sectors in directory
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push si ; (si) = BytesPerSector
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mov bx, DirSeg
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mov es, bx
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assume es:DirSeg
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xor bx, bx ; (es:bx) -> directory segment
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; NTLDR is supposed to occupy 1st 512 entries
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; in the root directory.
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xor dx, dx
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mov ax, (512*32) ; (dx:ax) = 4000h
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div si ; (si) = BytesPerSector
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;
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; DoRead does a RETF, but LINK pukes if we do a FAR call in a /tiny program.
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;
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; (ax) = # of sectors to read
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;
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push ax
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push cs ; make retern frame
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call DoRead ; read directory
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pop ax
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jc BootErr$he
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; Now we scan for the presence of NTLDR
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xor bx, bx ; offset
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mov cx, 512 ; # of entries to search (only 512)
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Rpt01:
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mov di, bx ; (es:di) = filespec in directory entry
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push cx
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mov cx, 11 ; (cx) = filespec size
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mov si, offset LOADERNAME ; (ds:si) = filespec we are searching
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repe cmpsb
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pop cx
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je @F ; if matches, exit loop
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add bx, size DIR_ENT ; else next entry
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loop Rpt01
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@@:
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test cx, cx
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pop si
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pop cx
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jnz Rpt02
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add NtldrSharedData.Arguments.SectorBase.lsw, ax
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adc NtldrSharedData.Arguments.SectorBase.msw, 0
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sub cx, ax
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ja Rpt00
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jmp BootErr$bnf
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Rpt02:
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; We have found NTLDR
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; We read it into NtLdrSeg.
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mov dx, es:[bx].StartCluster ; (dx) = starting cluster number
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mov ax, 1 ; (ax) = sectors to read
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cmp BytesPerSector, 256
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jne @F
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inc ax ; We need to read 2 sectors
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@@:
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;
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; Now, go read the file
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;
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mov bx, NtLdrSeg
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mov es, bx
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assume es:NtLdrSeg
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xor bx, bx ; (es:bx) -> start of NTLDR
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;
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; LINK barfs if we do a FAR call in a TINY program, so we have to fake it
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; out by pushing CS.
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;
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push dx ; save starting cluster number
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push cs ; make retern frame
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call ClusterRead
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pop bx ; (bx) = Starting Cluster Number
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jc BootErr$he
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;
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; NTLDR requires:
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; BX = Starting Cluster Number of NTLDR
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; DL = INT 1B drive number we booted from <- DA/UA in 98
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; DS:SI -> the boot media's BPB
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; DS:DI -> argument structure
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; 1000:0000 - entire DIR is loaded
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; On PC-9801 we have one more parameter...
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; (bp) = partition info
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;
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lea si, BPB ; ds:si -> BPB
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lea di, NtldrSharedData.Arguments ; ds:di -> Arguments
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mov ax,ds
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mov NtldrSharedData.Arguments.ReadClusters.msw, ax
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mov NtldrSharedData.Arguments.ReadClusters.lsw, offset ClusterRead
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mov NtldrSharedData.Arguments.ReadSectors.msw, ax
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mov NtldrSharedData.Arguments.ReadSectors.lsw, offset DoRead
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mov dl, DriveNumber ; dl = boot drive
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pop bp ; partition info
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;
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; FAR JMP to 2000:0003. This is hand-coded, because I can't figure out
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; how to make MASM do this for me. By entering NTLDR here, we skip the
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; initial jump and execute the FAT-specific code to load the rest of
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; NTLDR.
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;
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db 0EAh ; JMP FAR PTR
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dw 3 ; 2000:3
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dw 02000h
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FATBOOT endp
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;
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; BootErr - print error message and hang the system.
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;
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BootErr proc
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BootErr endp
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; BootError - print error message and hang the system.
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;
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BootError proc
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assume DS:BootCode,ES:nothing
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;
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; Am I display message that is reason of the ERROR ?
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; Ofcourse. but no room available.
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BootErr$bnf:
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BootErr$he:
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mov al, 06h
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out 37h, al
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jmp $
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BootError endp
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;
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; ClusterRead - read AL sectors into ES:BX starting from
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; cluster DX
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;
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ClusterRead proc
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push ax ; (TOS) = # of sectors to read
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dec dx
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dec dx ; adjust for reserved clusters 0 and 1
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mov al, SectorsPerCluster
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xor ah, ah
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mul dx ; DX:AX = starting sector number
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add ax, NtldrSharedData.ClusterBase ; adjust for FATs, root dir, boot sec.
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adc dx, 0
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mov NtldrSharedData.Arguments.SectorBase.lsw, ax
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mov NtldrSharedData.Arguments.SectorBase.msw, dx
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pop ax ; (al) = # of sectors to read
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;
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; Now we've converted the cluster number to a SectorBase, so just fall
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; through into DoRead
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;
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ClusterRead endp
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|
|
|
||
|
|
;
|
||
|
|
; DoRead - read AL sectors into ES:BX starting from sector
|
||
|
|
; SectorBase.
|
||
|
|
;
|
||
|
|
DoRead proc
|
||
|
|
xor ah, ah
|
||
|
|
cmp ax, 0
|
||
|
|
jnz @F
|
||
|
|
|
||
|
|
inc ah ; read 256 Sectors
|
||
|
|
@@:
|
||
|
|
push si
|
||
|
|
push di
|
||
|
|
push bp
|
||
|
|
|
||
|
|
mov si, ax
|
||
|
|
mov bp, bx
|
||
|
|
mov cx, NtldrSharedData.Arguments.SectorBase.lsw ; Starting sector
|
||
|
|
mov dx, NtldrSharedData.Arguments.SectorBase.msw ; Starting sector
|
||
|
|
|
||
|
|
; (dx:cx) = logical sector # relative to partition
|
||
|
|
; (si) = # of sectors to read
|
||
|
|
; (es:bp) = read buffer
|
||
|
|
|
||
|
|
Rpt03:
|
||
|
|
push dx
|
||
|
|
push cx
|
||
|
|
|
||
|
|
; [sp] = logical sector number LSW
|
||
|
|
; [sp+2] = logical sector number MSW
|
||
|
|
|
||
|
|
mov al, DriveNumber
|
||
|
|
|
||
|
|
test al, DAFloppy
|
||
|
|
jz Flg03
|
||
|
|
|
||
|
|
; We are reading floppy disk.
|
||
|
|
; We don't care about DMA boundary, as no PC-9801 DOS floppy disk
|
||
|
|
; has more than 2048 directory entries, we never read
|
||
|
|
; more than 64 KB.
|
||
|
|
|
||
|
|
push ax
|
||
|
|
mov ax, cx ; (dx:ax) = lsn
|
||
|
|
mov bx, SectorsPerTrack
|
||
|
|
div bx ; (dx) = sector # (0-based)
|
||
|
|
; (ax) = cylinder # * # of heads + head #
|
||
|
|
div byte ptr Heads ;(ah) = head address
|
||
|
|
; (al) = cylinder address
|
||
|
|
mov dh, ah
|
||
|
|
mov cl, al
|
||
|
|
mov al, byte ptr BytesPerSector + 1 ; convert Bytes/Sector to
|
||
|
|
xor ch, ch ; SectorLengthID
|
||
|
|
whl00: ; Bytes/Sect | ID (ch)
|
||
|
|
cmp al, 0
|
||
|
|
jz @f
|
||
|
|
|
||
|
|
inc ch ; 128 -> 0
|
||
|
|
shr al, 1 ; 256 -> 1
|
||
|
|
jmp short whl00 ; 512 -> 2
|
||
|
|
@@: ; 1024 -> 3
|
||
|
|
pop ax
|
||
|
|
|
||
|
|
sub bl, dl ; sectors in THIS track
|
||
|
|
inc dl ; sector # (1-based)
|
||
|
|
|
||
|
|
; We have prepared following ROM BIOS parameters
|
||
|
|
; (al) = drive
|
||
|
|
; (cl) = cylinder address
|
||
|
|
; (ch) = sector size
|
||
|
|
; (dl) = sector address
|
||
|
|
; (dh) = head address
|
||
|
|
; (es:bp) -> buffer
|
||
|
|
;
|
||
|
|
; And we have some more.
|
||
|
|
; (bl) = # of sectors we can read with 1 time ROM call
|
||
|
|
; (si) = # of sectors we need to read
|
||
|
|
;
|
||
|
|
jmp short Flg04
|
||
|
|
|
||
|
|
Flg03:
|
||
|
|
; We are reading hard disk.
|
||
|
|
; We don't care about DMA boundary
|
||
|
|
; as length we read is 64KB max.
|
||
|
|
;
|
||
|
|
|
||
|
|
and al, 7FH ; drive #
|
||
|
|
mov bx,NtldrSharedData.SectorShiftFactor
|
||
|
|
|
||
|
|
Rpt04: ; logical sector address to
|
||
|
|
shr bx, 1
|
||
|
|
jc @F
|
||
|
|
|
||
|
|
shl cx, 1 ; physical sector address
|
||
|
|
rcl dx, 1
|
||
|
|
jmp short Rpt04
|
||
|
|
@@:
|
||
|
|
add cx, HiddenSectors.lsw
|
||
|
|
adc dx, HiddenSectors.msw ; (dx:cx) -> relative to drive
|
||
|
|
mov bl, NtldrSharedData.LogicalSectorsIn32KByte
|
||
|
|
; sectors we can read (32KB)
|
||
|
|
; this is not optimum on performance
|
||
|
|
|
||
|
|
; We have prepared following ROM BIOS parameters
|
||
|
|
; (al) = drive
|
||
|
|
; (dx:cx) = relative sector number
|
||
|
|
; (es:bp) -> buffer
|
||
|
|
;
|
||
|
|
; And we have some more.
|
||
|
|
; (bl) = # of sectors we can read with 1 time ROM call
|
||
|
|
; (si) = # of sectors we need to read
|
||
|
|
;
|
||
|
|
Flg04:
|
||
|
|
|
||
|
|
xor bh, bh
|
||
|
|
|
||
|
|
cmp si, bx
|
||
|
|
jnb @F
|
||
|
|
|
||
|
|
mov bx, si
|
||
|
|
@@:
|
||
|
|
push bx ; # of sectors we are reading this call
|
||
|
|
push dx
|
||
|
|
xchg ax, bx
|
||
|
|
mul BytesPerSector
|
||
|
|
xchg ax, bx
|
||
|
|
pop dx
|
||
|
|
push bx ; # of bytes.
|
||
|
|
|
||
|
|
; [sp] = # of bytes to read
|
||
|
|
; [sp+2] = # of sectors
|
||
|
|
; [sp+4] = logical sector number LSW
|
||
|
|
; [sp+6] = logical sector number MSW
|
||
|
|
|
||
|
|
mov ah, 01010110b ; read
|
||
|
|
int 1BH
|
||
|
|
|
||
|
|
pop di ; # of bytes
|
||
|
|
pop bx ; # of sectors
|
||
|
|
pop cx ; lsn (LSW)
|
||
|
|
pop dx ; lsn (MSW)
|
||
|
|
|
||
|
|
jc @F ; return Carry
|
||
|
|
|
||
|
|
; prepare for next call
|
||
|
|
|
||
|
|
add cx, bx ; advance lsn
|
||
|
|
adc dx, 0 ;
|
||
|
|
add bp, di ; advance offset
|
||
|
|
sub si, bx ; decrement # of sectors
|
||
|
|
jnz Rpt03 ; CarryFlag is Clear
|
||
|
|
@@:
|
||
|
|
|
||
|
|
pop bp
|
||
|
|
pop di
|
||
|
|
pop si
|
||
|
|
retf
|
||
|
|
DoRead endp
|
||
|
|
|
||
|
|
LOADERNAME DB "NTLDR "
|
||
|
|
|
||
|
|
; .errnz ($-FATBOOT) GT 510,<FATAL PROBLEM: boot sector is too large>
|
||
|
|
|
||
|
|
org 510
|
||
|
|
db 55h, 0aah
|
||
|
|
|
||
|
|
BootCode ends
|
||
|
|
|
||
|
|
;Unitialized variables go here--beyond the end of the boot sector in free memory
|
||
|
|
UninitializedWork struc
|
||
|
|
ClusterBase dw ? ; first sector of cluster # 2
|
||
|
|
SectorShiftFactor dw ?
|
||
|
|
LogicalSectorsIn32KByte db ?
|
||
|
|
Arguments db (size SHARED) dup (?) ; structure passed to NTLDR
|
||
|
|
UninitializedWork ends
|
||
|
|
|
||
|
|
END FATBOOT
|