; responsibility is to locate the booter partition, load the
; booter into memory, and jump to the booter's entry point.
; The booter partition can be a primary or a logical partition.
-; But the booter partition must reside within the 8GB limit
-; imposed by CHS addressing + translation.
;
; This boot loader can be placed at any of the following places:
-; * Master Boot Record (MBR)
-; * Boot sector of an extended partition
-; * Boot sector of a primary partition
-; * Boot sector of a logical partition
+; 1. Master Boot Record (MBR)
+; 2. Boot sector of an extended partition
+; 3. Boot sector of a primary partition
+; 4. Boot sector of a logical partition
;
; In order to coexist with a fdisk partition table (64 bytes), and
; leave room for a two byte signature (0xAA55) in the end, boot0 is
; restricted to 446 bytes (512 - 64 - 2). If boot0 did not have to
-; live in the MBR, then we would have 510 bytes to play with.
+; live in the MBR, then we would have 510 bytes to work with.
;
-; boot0 is always loaded by the BIOS or another first level booter
-; to 0:7C00h.
+; boot0 is always loaded by the BIOS or another booter to 0:7C00h.
;
; This code is written for the NASM assembler.
; nasm boot0.s -o boot0
-;--------------------------------------------------------------------------
-; Constants.
-DEBUG EQU 0 ; enable debugging output
+;
+; Set to 1 to enable obscure debug messages.
+;
+DEBUG EQU 0
+
+;
+; Set to 1 to support loading the booter (boot2) from a
+; logical partition.
+;
+EXT_PART_SUPPORT EQU 1
+
+;
+; Various constants.
+;
+kBoot0Segment EQU 0x0000
+kBoot0Stack EQU 0xFFF0 ; boot0 stack pointer
+kBoot0LoadAddr EQU 0x7C00 ; boot0 load address
+kBoot0RelocAddr EQU 0xE000 ; boot0 relocated address
+
+kMBRBuffer EQU 0x1000 ; MBR buffer address
+kExtBuffer EQU 0x1200 ; EXT boot block buffer address
-BOOTSEG EQU 0x0 ; our sole segment
-BOOTSP EQU 0xFFF0 ; stack pointer
-BOOTLOAD EQU 0x7C00 ; booter load address
-BOOTRELOC EQU 0xE000 ; booter is relocated here
-BOOTSIG EQU 0xAA55 ; booter signature
+kPartTableOffset EQU 0x1be
+kMBRPartTable EQU kMBRBuffer + kPartTableOffset
+kExtPartTable EQU kExtBuffer + kPartTableOffset
-BOOT2_SIZE EQU 88 ; load this many blocks for boot2
-BOOT2_ADDR EQU 0x3000 ; where to load boot2
+kBoot2Sectors EQU 112 ; sectors to load for boot2
+kBoot2Address EQU 0x0000 ; boot2 load address
+kBoot2Segment EQU 0x2000 ; boot2 load segment
-DRIVE_NUM EQU 0x80 ; "C" drive
-SECTOR_BYTES EQU 512 ; sector size in bytes
+kSectorBytes EQU 512 ; sector size in bytes
+kBootSignature EQU 0xAA55 ; boot sector signature
-BUF_MBR EQU 0x1000 ; memory buffer for MBR
-BUF_EXT EQU 0x1200 ; memory buffer for extended partition
+kPartCount EQU 4 ; number of paritions per table
+kPartTypeBoot EQU 0xab ; boot2 partition type
+kPartTypeExtDOS EQU 0x05 ; DOS extended partition type
+kPartTypeExtWin EQU 0x0f ; Windows extended partition type
+kPartTypeExtLinux EQU 0x85 ; Linux extended partition type
-TABLE_MAIN EQU BUF_MBR + 0x1be ; location of main partition table
-TABLE_EXT EQU BUF_EXT + 0x1be ; location of ext partition table
-ENTRY_SIZE EQU 16 ; size of each fdisk partition entry
-TYPE_BOOT EQU 0xab ; partition type we are looking for
-TYPE_EXT EQU 0x05 ; extended partition type
-TYPE_EXT_1 EQU 0x0f ; Windows extended partition
-TYPE_EXT_2 EQU 0x85 ; Linux extended partition
-EXT_LEVELS_MAX EQU 128 ; max extended partition levels
+%ifdef FLOPPY
+kDriveNumber EQU 0x00
+%else
+kDriveNumber EQU 0x80
+%endif
+
+;
+; In memory variables.
+;
+ebios_lba dd 0 ; starting LBA of the intial extended partition.
+read_func dw 0 ; pointer to the LBA or CHS read function
-; Disk parameters gathered through INT13/F8 call.
;
-max_sectors db 0 ; number of sectors per track
-max_heads db 0 ; number of heads
+; Format of fdisk partition entry.
+;
+; The symbol 'part_size' is automatically defined as an `EQU'
+; giving the size of the structure.
+;
+ struc part
+.bootid: resb 1 ; bootable or not
+.head: resb 1 ; starting head, sector, cylinder
+.sect: resb 1 ;
+.cyl: resb 1 ;
+.type: resb 1 ; partition type
+.endhead resb 1 ; ending head, sector, cylinder
+.endsect: resb 1 ;
+.endcyl: resb 1 ;
+.lba: resd 1 ; starting lba
+.sectors resd 1 ; size in sectors
+ endstruc
-; Parameters to our load function.
;
-chs_cx dw 0 ; cx register for INT13/F2 call
-chs_dx dw 0 ; dx register for INT13/F2 call
+; Macros.
+;
+%macro DebugCharMacro 1
+ mov al, %1
+ call print_char
+%endmacro
+%if DEBUG
+%define DebugChar(x) DebugCharMacro x
+%else
+%define DebugChar(x)
+%endif
;--------------------------------------------------------------------------
; Start of text segment.
SEGMENT .text
- ORG 0xE000 ; must match BOOTRELOC
+ ORG 0xE000 ; must match kBoot0RelocAddr
;--------------------------------------------------------------------------
-; Loaded at 0:7c00h.
+; Boot code is loaded at 0:7C00h.
;
start
- ; Set up the stack to grow down from BOOTSEG:BOOTSP.
+ ;
+ ; Set up the stack to grow down from kBoot0Segment:kBoot0Stack.
; Interrupts should be off while the stack is being manipulated.
;
- cli ; interrupts off
- mov ax, BOOTSEG ;
- mov ss, ax ; ss <- BOOTSEG
- mov sp, BOOTSP ; sp <- BOOTSP
- sti ; reenable interrupts
+ cli ; interrupts off
+ xor ax, ax ; zero ax
+ mov ss, ax ; ss <- 0
+ mov sp, kBoot0Stack ; sp <- top of stack
+ sti ; reenable interrupts
+
+ mov es, ax ; es <- 0
+ mov ds, ax ; ds <- 0
- ; Relocate the booter code from DS:SI to ES:DI,
- ; or from 0:7C00h to BOOTSEG:BOOTRELOC.
;
- mov es, ax ; es <- BOOTSEG
- xor ax, ax
- mov ds, ax ; ds <- 0
- mov si, BOOTLOAD ; si <- BOOTLOAD (source)
- mov di, BOOTRELOC ; di <- BOOTRELOC (destination)
+ ; Relocate boot0 code.
;
- cld ; auto-increment SI and/or DI registers
- mov cx, 256 ; copy 256 words (512 bytes)
- repnz movsw ; repeat string move (word) operation
+ mov si, kBoot0LoadAddr ; si <- source
+ mov di, kBoot0RelocAddr ; di <- destination
+ ;
+ cld ; auto-increment SI and/or DI registers
+ mov cx, kSectorBytes/2 ; copy 256 words
+ repnz movsw ; repeat string move (word) operation
; Code relocated, jump to start_reloc in relocated location.
;
- jmp BOOTSEG:start_reloc
+ jmp 0:start_reloc
;--------------------------------------------------------------------------
; Start execution from the relocated location.
;
-start_reloc
- mov ax, BOOTSEG
- mov ds, ax ; ds <- BOOTSEG
+start_reloc:
+
+ DebugChar('>')
- mov al, '=' ; indicate execution start
- call putchar
+ mov dl, kDriveNumber ; starting BIOS drive number
+
+.loop:
+
+%if DEBUG
+ mov al, dl
+ call print_hex
+%endif
- ; Get disk parameters (CHS) using INT13/F8 call.
;
- mov dl, DRIVE_NUM ; boot drive is drive C
- mov ah, 8 ; Read Disk Driver Parameter function
- int 0x13
- and cl, 0x3f ; sectors/track
- mov [max_sectors], cl
- mov [max_heads], dh
- jc error
-
- mov al, '>' ; indicate INT13/F8 success
- call putchar
-
- ; Since this code may not always reside in the MBR, we will always
- ; start by loading the MBR to BUF_MBR.
- ;
- mov WORD [chs_cx], 0x0001 ; cyl = 0, sect = 1
- mov BYTE [chs_dx + 1], 0 ; head = 0
- xor cx, cx ; skip 0 sectors
- mov ax, 1 ; read 1 sector
- mov bx, BUF_MBR ; load buffer
+ ; Clear various flags in memory.
+ ;
+ xor eax, eax
+ mov [ebios_lba], eax ; clear EBIOS LBA offset
+ mov WORD [read_func], read_chs ; assume CHS support
+
+ ;
+ ; Since this code may not always reside in the MBR, always start by
+ ; loading the MBR to kMBRBuffer.
+ ;
+ mov al, 1 ; load one sector
+ xor bx, bx
+ mov es, bx ; MBR load segment = 0
+ mov bx, kMBRBuffer ; MBR load address
+ mov si, bx ; pointer to fake partition entry
+ mov WORD [si], 0x0000 ; CHS DX: head = 0
+ mov WORD [si + 2], 0x0001 ; CHS CX: cylinder = 0, sector = 1
+
call load
- jc error
+ jc .next_drive ; MBR load error
- mov di, TABLE_MAIN ; argument for find_booter
- cmp WORD [di + 64], BOOTSIG ; correct signature found?
- jne error ; Oops! no signature!
- mov bl, TYPE_BOOT ; look for this partition type
- mov bh, 0 ; initial nesting level is 0
- call find_booter
+ ;
+ ; Check if EBIOS is supported for this hard drive.
+ ;
+ mov ah, 0x41 ; Function 0x41
+ mov bx, 0x55AA ; check signature
+; mov dl, kDriveNumber ; Drive number
+ int 0x13
-error
- mov si, load_error
- call message
-hang_1
- jmp hang_1
+ ;
+ ; If successful, the return values are as follows:
+ ;
+ ; carry = 0
+ ; ah = major version of EBIOS extensions (0x21 = version 1.1)
+ ; al = altered
+ ; bx = 0xAA55
+ ; cx = support bits. bit 0 must be set for function 0x42.
+ ;
+ jc .ebios_check_done
+ cmp bx, 0xAA55 ; check BX = 0xAA55
+ jnz .ebios_check_done
+ test cl, 0x01 ; check enhanced drive read support
+ mov WORD [read_func], read_lba ; use read_lba for reads
+ DebugChar('E') ; EBIOS supported
+.ebios_check_done:
+
+ ;
+ ; Look for the booter partition in the MBR partition table,
+ ; which is at offset kMBRPartTable.
+ ;
+ mov di, kMBRPartTable ; pointer to partition table
+ mov ah, 0 ; initial nesting level is 0
+ call find_boot ; will not return on success
+
+.next_drive:
+ inc dl ; next drive number
+ test dl, 0x4 ; went through all 4 drives?
+ jz .loop ; not yet, loop again
+
+ mov si, boot_error_str
+ call print_string
+
+hang:
+ jmp SHORT hang
;--------------------------------------------------------------------------
-; Locate the booter partition and load the booter.
+; Find the boot partition and load the booter from the partition.
;
; Arguments:
-; di - pointer to fdisk partition table.
-; bl - partition type to look for.
+; AH = recursion nesting level
+; DL = drive number (0x80 + unit number)
+; DI = pointer to fdisk partition table.
;
-; The following registers are modified:
-; ax, bh
+; Clobber list:
+; AX, BX, EBP
;
-find_booter
- push cx
+find_boot:
+ push cx ; preserve CX and SI
push si
- mov si, di ; si <- pointer to partition table
- mov cx, 4 ; 4 partition entries per table
-
-find_booter_pri
;
- ; Hunt for a fdisk partition type that matches the value in bl.
+ ; Check for boot block signature 0xAA55 following the 4 partition
+ ; entries.
;
-%IF DEBUG
- mov al, bh ; log partition type seen
- call putspace
- mov al, [si + 4]
- call display_byte
-%ENDIF
-
- cmp BYTE [si + 4], bl ; Is this the booter partition?
- je load_booter ; yes, load the booter
+ cmp WORD [di + part_size * kPartCount], kBootSignature
+ jne .exit ; boot signature not found
- add si, ENTRY_SIZE ; si <- next partition entry
- loop find_booter_pri ; loop while cx is not zero
+ mov si, di ; make SI a pointer to partition table
+ mov cx, kPartCount ; number of partition entries per table
- ; No primary (or perhaps logical) booter partition found in the
- ; current partition table. Restart and look for extended partitions.
+.loop:
;
- mov si, di ; si <- pointer to partition table
- mov cx, 4 ; 4 partition entries per table
+ ; First scan through the partition table looking for the boot
+ ; partition. Postpone walking the extended partition chain for
+ ; the second pass. Do not merge the two without changing the
+ ; buffering scheme used to store extended partition tables.
+ ;
+%if DEBUG
+ mov al, ah ; indent based on nesting level
+ call print_spaces
+ mov al, [si + part.type] ; print partition type
+ call print_hex
+%endif
+
+ cmp BYTE [si + part.type], kPartTypeBoot
+ jne .continue
-find_booter_ext
;
- ; Look for extended partition entries in the partition table.
+ ; Found boot partition, read boot2 image to memory.
;
-%IF DEBUG
- mov al, bh ; log partition type seen
- call putspace
- mov al, 'E'
- call putchar
- mov al, [si + 4]
- call display_byte
-%ENDIF
+ mov al, kBoot2Sectors
+ mov bx, kBoot2Segment
+ mov es, bx
+ mov bx, kBoot2Address
+ call load ; will not return on success
+ jc .continue ; load error, keep looking?
- cmp BYTE [si + 4], TYPE_EXT ; Is this an extended partition?
- je find_booter_ext_2 ; yes, load its partition table
+ ;
+ ; Jump to boot2. The drive number is already in register DL.
+ ;
+ ; The first sector loaded from the disk is reserved for the boot
+ ; block (boot0), adjust the jump location by adding a sector offset.
+ ;
+ jmp kBoot2Segment:kBoot2Address + kSectorBytes
- cmp BYTE [si + 4], TYPE_EXT_1 ; Is this an extended partition?
- je find_booter_ext_2 ; yes, load its partition table
-
- cmp BYTE [si + 4], TYPE_EXT_2 ; Is this an extended partition?
- je find_booter_ext_2 ; yes, load its partition table
+.continue:
+ add si, part_size ; advance SI to next partition entry
+ loop .loop ; loop through all partition entries
-find_booter_ext_1
+%if EXT_PART_SUPPORT
;
- ; si is not pointing to an extended partition entry,
- ; try the next entry in the partition table.
+ ; No primary (or logical) boot partition found in the current
+ ; partition table. Restart and look for extended partitions.
;
- add si, ENTRY_SIZE ; si <- next partition entry
- loop find_booter_ext ; loop while cx is not zero
+ mov si, di ; make SI a pointer to partition table
+ mov cx, kPartCount ; number of partition entries per table
- jmp find_booter_end ; give up
+.ext_loop:
-find_booter_ext_2
- cmp bh, EXT_LEVELS_MAX
- ja find_booter_end ; in too deep!
+ mov al, [si + part.type] ; AL <- partition type
- inc bh ; increment nesting level counter
+ cmp al, kPartTypeExtDOS ; Extended DOS
+ je .ext_load
- ; Prepare the arguments for the load function call to
- ; load the extended partition table into memory.
- ; Note that si points to the extended partition entry.
- ;
- mov ax, [si] ; DH/DL
- mov [chs_dx], ax
- mov ax, [si + 2] ; CH/CL
- mov [chs_cx], ax
- pusha
- xor cx, cx ; skip 0 sectors
- mov ax, 1 ; read 1 sector
- mov bx, BUF_EXT ; load to BUF_EXT
- call load
- popa
+ cmp al, kPartTypeExtWin ; Extended Windows(95)
+ je .ext_load
- jc find_booter_ext_3 ; bail out if load failed
+ cmp al, kPartTypeExtLinux ; Extended Linux
+ je .ext_load
- mov di, TABLE_EXT ; di <- pointer to new partition table
- cmp WORD [di + 64], BOOTSIG
- jne find_booter_ext_3 ; OhOh! no signature!
+.ext_continue:
+ ;
+ ; Advance si to the next partition entry in the extended
+ ; partition table.
+ ;
+ add si, part_size ; advance SI to next partition entry
+ loop .ext_loop ; loop through all partition entries
+ jmp .exit ; boot partition not found
- call find_booter ; recursion...
+.ext_load:
+ ;
+ ; Setup the arguments for the load function call to bring the
+ ; extended partition table into memory.
+ ; Remember that SI points to the extended partition entry.
+ ;
+ mov al, 1 ; read 1 sector
+ xor bx, bx
+ mov es, bx ; es = 0
+ mov bx, kExtBuffer ; load extended boot sector
+ call load
+ jc .ext_continue ; load error
-find_booter_ext_3
- dec bh ; decrement nesting level counter
+ ;
+ ; The LBA address of all extended partitions is relative based
+ ; on the LBA address of the extended partition in the MBR, or
+ ; the extended partition at the head of the chain. Thus it is
+ ; necessary to save the LBA address of the first extended partition.
+ ;
+ or ah, ah
+ jnz .ext_find_boot
+ mov ebp, [si + part.lba]
+ mov [ebios_lba], ebp
+
+.ext_find_boot:
+ ;
+ ; Call find_boot recursively to scan through the extended partition
+ ; table. Load DI with a pointer to the extended table in memory.
+ ;
+ inc ah ; increment recursion level
+ mov di, kExtPartTable ; partition table pointer
+ call find_boot ; recursion...
+ ;dec ah
- ; If we got here, then we know there isn't a booter
- ; partition linked from this partition entry.
+ ;
+ ; Since there is an "unwritten" rule that limits each partition table
+ ; to have 0 or 1 extended partitions, there is no point in looking for
+ ; any additional extended partition entries at this point. There is no
+ ; boot partition linked beyond the extended partition that was loaded
+ ; above.
+ ;
- test bh, bh ; if we are at level 0, then
- jz find_booter_ext_1 ; look for next extended partition entry
+%endif ; EXT_PART_SUPPORT
-find_booter_end
+.exit:
+ ;
+ ; Boot partition not found. Giving up.
+ ;
pop si
pop cx
ret
;--------------------------------------------------------------------------
-; Yeah! Found the booter partition. The first sector in this partition
-; is reserved for the boot sector code (us). So load the booter
-; starting from the second sector in the partition, then jump to the
-; start of the booter.
-;
-load_booter
- mov ax, [si] ; DH/DL
- mov [chs_dx], ax
- mov ax, [si + 2] ; CH/CL
- mov [chs_cx], ax
-
- mov cx, 1 ; skip the initial boot sector
- mov ax, BOOT2_SIZE ; read BOOT2_SIZE sectors
- mov bx, BOOT2_ADDR ; where to place boot2 code
- call load ; load it...
-
- xor edx, edx ; argument for boot2 (hard drive boot)
- jmp BOOTSEG:BOOT2_ADDR ; there is no going back now!
-
-;--------------------------------------------------------------------------
-; Load sectors from disk using INT13/F2 call. The sectors are loaded
-; one sector at a time to avoid any BIOS bugs, and eliminate
-; complexities with crossing track boundaries, and other gotchas.
+; load - Load one or more sectors from a partition.
;
; Arguments:
-; cx - number of sectors to skip
-; ax - number of sectors to read
-; bx - pointer to the memory buffer (must not cross a segment boundary)
-; [chs_cx][chs_dx] - CHS starting position
+; AL = number of 512-byte sectors to read.
+; ES:BX = pointer to where the sectors should be stored.
+; DL = drive number (0x80 + unit number)
+; SI = pointer to the partition entry.
;
; Returns:
-; CF = 0 success
-; CF = 1 error
-;
-; The caller must save any registers it needs.
-;
-load
- jcxz load_sectors
- call next_sector ; [chs_cx][chs_dx] <- next sector
- loop load
-
-load_sectors
- mov cx, ax ; cx <- number of sectors to read
-
-load_loop
- call read_sector ; load a single sector
- jc load_exit ; abort if carry flag is set
- add bx, SECTOR_BYTES ; increment buffer pointer
- call next_sector ; [chs_cx][chs_dx] <- next sector
- loop load_loop
- clc ; successful exit
-load_exit
+; CF = 0 success
+; 1 error
+;
+load:
+ push cx
+ mov cx, 5 ; number of times to retry
+
+.loop:
+ call [read_func] ; call either read_chs or read_lba
+ jnc .exit ; load success
+ loop .loop ; retry on error
+
+.exit:
+ pop cx
ret
;--------------------------------------------------------------------------
-; Read a single sector from the hard disk.
+; read_chs - Read sectors from a partition using CHS addressing.
;
; Arguments:
-; [chs_cx][chs_dx] - CHS starting position
-; bx - pointer to the sector memory buffer
-; (must not cross a segment boundary)
+; AL = number of 512-byte sectors to read.
+; ES:BX = pointer to where the sectors should be stored.
+; DL = drive number (0x80 + unit number)
+; SI = pointer to the partition entry.
;
; Returns:
-; CF = 0 success
-; CF = 1 error
-;
-; Caller's cx register is preserved.
+; CF = 0 success
+; 1 error
;
-read_sector
- push cx
- mov cx, 5 ; try 5 times to read the sector
-
-read_sector_1
- mov bp, cx ; save cx
+read_chs:
+ pusha ; save all registers
- mov cx, [chs_cx]
- mov dx, [chs_dx]
- mov dl, DRIVE_NUM ; drive number
- mov ax, 0x0201 ; Func 2, read 1 sector
- int 0x13 ; read sector
- jnc read_sector_ok ; CF = 0 indicates success
-
- mov al, '*' ; sector read error indicator
- call putchar
+ ;
+ ; Read the CHS start values from the partition entry.
+ ;
+ mov dh, [ si + part.head ] ; drive head
+ mov cx, [ si + part.sect ] ; drive sector + cylinder
- xor ax, ax ; Reset the drive and retry the read
- int 0x13
+ ;
+ ; INT13 Func 2 - Read Disk Sectors
+ ;
+ ; Arguments:
+ ; AH = 2
+ ; AL = number of sectors to read
+ ; CH = lowest 8 bits of the 10-bit cylinder number
+ ; CL = bits 6 & 7: cylinder number bits 8 and 9
+ ; bits 0 - 5: starting sector number (1-63)
+ ; DH = starting head number (0 to 255)
+ ; DL = drive number (80h + drive unit)
+ ; es:bx = pointer where to place sectors read from disk
+ ;
+ ; Returns:
+ ; AH = return status (sucess is 0)
+ ; AL = burst error length if ah=0x11 (ECC corrected)
+ ; carry = 0 success
+ ; 1 error
+ ;
+; mov dl, kDriveNumber
+ mov ah, 0x02 ; Func 2
+ int 0x13 ; INT 13
+ jnc .exit
- mov cx, bp
- loop read_sector_1 ; retry while cx is not zero
+ DebugChar('e') ; indicate INT13/F2 error
- stc ; set carry flag to indicate error
- pop cx
- ret
+ ;
+ ; Issue a disk reset on error.
+ ; Should this be changed to Func 0xD to skip the diskette controller
+ ; reset?
+ ;
+ xor ax, ax ; Func 0
+ int 0x13 ; INT 13
+ stc ; set carry to indicate error
-read_sector_ok
- mov al, '.' ; successful sector read indicator
- call putchar
- clc ; success, clear carry flag
- pop cx
+.exit:
+ popa
ret
;--------------------------------------------------------------------------
-; Given the current CHS position stored in [chs_cx][chs_dx], update
-; it so that the value in [chs_cx][chs_dx] points to the following
-; sector.
+; read_lba - Read sectors from a partition using LBA addressing.
;
; Arguments:
-; [chs_cx][chs_dx] - CHS position
-;
-; [max_sectors] and [max_heads] must be valid.
+; AL = number of 512-byte sectors to read (valid from 1-127).
+; ES:BX = pointer to where the sectors should be stored.
+; DL = drive number (0x80 + unit number)
+; SI = pointer to the partition entry.
;
-; Caller's ax and bx registers are preserved.
+; Returns:
+; CF = 0 success
+; 1 error
;
-next_sector
- push ax
- push bx
+read_lba:
+ pusha ; save all registers
+ mov bp, sp ; save current SP
- ; Extract the CHS values from the packed register values in memory.
;
- mov al, [chs_cx]
- and al, 0x3f ; al <- sector number (1-63)
+ ; Create the Disk Address Packet structure for the
+ ; INT13/F42 (Extended Read Sectors) on the stack.
+ ;
- mov bx, [chs_cx]
- rol bl, 2
- ror bx, 8
- and bx, 0x03ff ; bx <- cylinder number
+ ; push DWORD 0 ; offset 12, upper 32-bit LBA
+ push ds ; For sake of saving memory,
+ push ds ; push DS register, which is 0.
- mov ah, [chs_dx + 1] ; ah <- head number
+ mov ecx, [ebios_lba] ; offset 8, lower 32-bit LBA
+ add ecx, [si + part.lba]
+ push ecx
- inc al ; Increment CHS by one sector.
- cmp al, [max_sectors]
- jbe next_sector_done
+ push es ; offset 6, memory segment
- inc ah
- cmp ah, [max_heads]
- jbe next_sector_new_head
+ push bx ; offset 4, memory offset
- inc bx
+ xor ah, ah ; offset 3, must be 0
+ push ax ; offset 2, number of sectors
-next_sector_new_cyl
- xor ah, ah ; head number starts at 0
+ push WORD 16 ; offset 0-1, packet size
-next_sector_new_head
- mov al, 1 ; sector number starts at 1
+ ;
+ ; INT13 Func 42 - Extended Read Sectors
+ ;
+ ; Arguments:
+ ; AH = 0x42
+ ; DL = drive number (80h + drive unit)
+ ; DS:SI = pointer to Disk Address Packet
+ ;
+ ; Returns:
+ ; AH = return status (sucess is 0)
+ ; carry = 0 success
+ ; 1 error
+ ;
+ ; Packet offset 2 indicates the number of sectors read
+ ; successfully.
+ ;
+; mov dl, kDriveNumber
+ mov si, sp
+ mov ah, 0x42
+ int 0x13
+
+ jnc .exit
-next_sector_done
- ; Reassemble the CHS values back into the packed representation
- ; in memory.
+ DebugChar('E') ; indicate INT13/F42 error
+
+ ;
+ ; Issue a disk reset on error.
+ ; Should this be changed to Func 0xD to skip the diskette controller
+ ; reset?
;
- mov [chs_cx + 1], bl ; lower 8-bits of the 10-bit cylinder
- ror bh, 2
- or bh, al
- mov [chs_cx], bh ; cylinder & sector number
- mov [chs_dx + 1], ah ; head number
+ xor ax, ax ; Func 0
+ int 0x13 ; INT 13
+ stc ; set carry to indicate error
- pop bx
- pop ax
+.exit:
+ mov sp, bp ; restore SP
+ popa
ret
;--------------------------------------------------------------------------
; Write a string to the console.
;
; Arguments:
-; ds:si pointer to a NULL terminated string.
-;
-; The following registers are modified:
-; ax, bx, si
-;
-message
- mov bx, 1 ; bh=0, bl=1 (blue)
- cld ; increment SI after each lodsb call
-message_loop
- lodsb ; load a byte from DS:SI into al
- cmp al, 0 ; Is it a NULL?
- je message_done ; yes, all done
- mov ah, 0xE ; bios INT10 Func 0xE
- int 0x10 ; bios display a byte in tty mode
- jmp short message_loop
-message_done
+; DS:SI pointer to a NULL terminated string.
+;
+; Clobber list:
+; AX, BX, SI
+;
+print_string
+ mov bx, 1 ; BH=0, BL=1 (blue)
+ cld ; increment SI after each lodsb call
+.loop
+ lodsb ; load a byte from DS:SI into AL
+ cmp al, 0 ; Is it a NULL?
+ je .exit ; yes, all done
+ mov ah, 0xE ; INT10 Func 0xE
+ int 0x10 ; display byte in tty mode
+ jmp short .loop
+.exit
ret
+%if DEBUG
+
;--------------------------------------------------------------------------
; Write a ASCII character to the console.
;
; Arguments:
-; al contains the ASCII character printed.
-;
-putchar
- push bx
- mov bx, 1 ; bh=0, bl=1 (blue)
- mov ah, 0x0e ; bios int 10, function 0xe
- int 0x10 ; bios display a byte in tty mode
- pop bx
- ret
-
-%IF DEBUG
-;==========================================================================
-; DEBUG FUNCTION START
+; AL = ASCII character.
;
-; If DEBUG is set to 1, this booter will become too large for the MBR,
-; but it will still be less than 510 bytes, which is fine for a partition's
-; boot sector.
-;==========================================================================
+print_char
+ pusha
+ mov bx, 1 ; BH=0, BL=1 (blue)
+ mov ah, 0x0e ; bios INT 10, Function 0xE
+ int 0x10 ; display byte in tty mode
+ popa
+ ret
;--------------------------------------------------------------------------
; Write a variable number of spaces to the console.
;
; Arguments:
-; al number to spaces to display
+; AL = number to spaces.
;
-putspace
- push cx
+print_spaces:
+ pusha
xor cx, cx
- mov cl, al ; use cx as the loop counter
- mov al, ' ' ; character to print
-putspace_loop
- jcxz putspace_done
- call putchar
- loop putspace_loop
-putspace_done
- pop cx
+ mov cl, al ; use CX as the loop counter
+ mov al, ' ' ; character to print
+.loop:
+ jcxz .exit
+ call print_char
+ loop .loop
+.exit:
+ popa
ret
;--------------------------------------------------------------------------
-; Write the hex byte value to the console.
+; Write the byte value to the console in hex.
;
; Arguments:
-; al contains the byte to be displayed. e.g. if al is 0x3f, then 3F
-; will be displayed on screen.
+; AL = Value to be displayed in hex.
;
-display_byte
+print_hex:
push ax
ror al, 4
- call display_nibble ; display upper nibble
+ call print_nibble ; display upper nibble
pop ax
- call display_nibble ; display lower nibble
- ;
- mov ax, 10 ; display carriage return
- call putchar
- mov ax, 13
- call putchar
+ call print_nibble ; display lower nibble
+
+ mov al, 10 ; carriage return
+ call print_char
+ mov al, 13
+ call print_char
ret
-display_nibble
+print_nibble:
and al, 0x0f
add al, '0'
cmp al, '9'
- jna display_nibble_1
+ jna .print_ascii
add al, 'A' - '9' - 1
-display_nibble_1
- call putchar
+.print_ascii:
+ call print_char
ret
-;==========================================================================
-; DEBUG FUNCTION END
-;==========================================================================
-%ENDIF
+%endif ; DEBUG
;--------------------------------------------------------------------------
; NULL terminated strings.
;
-load_error db 10, 13, 'Load Error', 0
+boot_error_str db 10, 13, 'Boot Error', 0
;--------------------------------------------------------------------------
; Pad the rest of the 512 byte sized booter with zeroes. The last
; that the 'times' argument is negative.
pad_boot
- times 446-($-$$) db 0
+ times 446-($-$$) db 0
+
+%ifdef FLOPPY
+;--------------------------------------------------------------------------
+; Put fake partition entries for the bootable floppy image
+;
+part1bootid db 0x80 ; first partition active
+part1head db 0x00 ; head #
+part1sect db 0x02 ; sector # (low 6 bits)
+part1cyl db 0x00 ; cylinder # (+ high 2 bits of above)
+part1systid db 0xab ; Apple boot partition
+times 3 db 0x00 ; ignore head/cyl/sect #'s
+part1relsect dd 0x00000001 ; start at sector 1
+part1numsect dd 0x00000080 ; 64K for booter
+part2bootid db 0x00 ; not active
+times 3 db 0x00 ; ignore head/cyl/sect #'s
+part2systid db 0xa8 ; Apple UFS partition
+times 3 db 0x00 ; ignore head/cyl/sect #'s
+part2relsect dd 0x00000082 ; start after booter
+; part2numsect dd 0x00000abe ; 1.44MB - 65K
+part2numsect dd 0x000015fe ; 2.88MB - 65K
+%endif
pad_table_and_sig
times 510-($-$$) db 0
- dw BOOTSIG
+ dw kBootSignature
END
projects / apple / boot.git / blobdiff