diff options
Diffstat (limited to 'bootblocks/mbr.s')
| -rw-r--r-- | bootblocks/mbr.s | 301 |
1 files changed, 203 insertions, 98 deletions
diff --git a/bootblocks/mbr.s b/bootblocks/mbr.s index a5a3923..fdfadca 100644 --- a/bootblocks/mbr.s +++ b/bootblocks/mbr.s @@ -2,27 +2,32 @@ ! This is a 'Master Boot Record' following the MSDOS 'standards'. ! This BB successfully boots MSDOS or Linux. ! -! In addition it has the facility to load and execute a small program -! before the boot blocks are checked. +! In addition it can: +! Display a message configure at install time. +! Load and execute a small program before the boot blocks are checked. ! ! Or ! -! Space for 12 extra partitions in the 'DiskManager' form that Linux -! _does_ understand. +! Space for 12 extra partitions in the 'Old Disk Manager' form that Linux +! _does_ understand (unfortunatly there doesn't appear to be an fdisk that +! understands them.) ! -! NB: This needs as86 0.15.2 or later +! NB: This needs as86 0.16.0 or later ! Lowest available is $0500, MSDOS appears to use $0600 ... I wonder why? ORGADDR=$0500 +copyright=1 ! Add in the copyright message; if room. preboot=0 ! Include the pre-boot loader. -mbrkey=0 ! Option to choose the boot record base on keystroke +mbrkey=0 ! Option to choose the boot record based on keystroke message=1 ! Display boot message use512=0 ! Put the end marker at byte 510..512 +markptab=1 ! Put an end marker just below the partition table. diskman=0 ! Disk manager partitions, allows 16 partitions but ! don't overwrite this with a LILO BB. -linear=0 ! Use the linear addresses not the CHS ones +linear=1 ! Use the linear addresses not the CHS ones (if available) +useCHS=1 ! Disable CHS if you need space. partition_start=ORGADDR+0x1BE partition_size=0x10 @@ -36,6 +41,12 @@ partition_end=ORGADDR+0x1FE table_start=partition_start endif +export linear +export diskman +export useCHS +export mbrkey +export preboot + org ORGADDR cli ! Assume _nothing_! cld @@ -54,7 +65,7 @@ org ORGADDR cont: sti ! Let the interrupts back in. -! Next check for a pre-boot load or a keypress +! Next check for a pre-boot message, load or keypress if message call disp_message endif @@ -65,23 +76,39 @@ cont: call key_wait endif + if (linear|useCHS) + ! Now check the partition table, must use SI as pointer cause that's what the ! partition boot blocks expect. +! If we're using diskman and we're short of space check the partitions in +! physical order. (Order. 4,3,2,1,5,6,7,8,9,10,11,12,13,14,15,16) + + if (diskman&linear&useCHS) + + mov si,#partition_end +check_next: + sub si,#partition_size + cmp byte [si],#$80 ! Flag for activated partition + jz found_active + cmp si,#low_partition + jnz check_next + + else + +! Normal active partition check, (Order: 1,2,3,4) mov si,#partition_start check_active: cmp byte [si],#$80 ! Flag for activated partition jz found_active - if mbrkey=0 -bad_boot: - endif +try_next_part: add si,#partition_size cmp si,#partition_end jnz check_active - ! Check for Disk manager partitions in the order that Linux numbers them. - if diskman - cmp word ptr diskman_magic,#$55AA +! Check for Disk manager partitions in the order that Linux numbers them. + if diskman&~(linear&useCHS) + cmp word ptr diskman_magic,#$AA55 jnz no_diskman mov si,#partition_start check_next: @@ -93,26 +120,78 @@ check_next: no_diskman: endif + endif + if mbrkey=0 +bad_boot: + endif mov si,#no_bootpart ! Message & boot jmp no_boot +! Active partition found, boot it. found_active: + mov di,#6 ! Max retries, int doc says 3 ... double it + movb [$7DFE],#0 ! Clear magic for dosemu +retry: + +! If the BIOS has LBA extensions use them. if linear - call linearise + if useCHS + mov ah,#$41 + mov bx,#$55AA + mov dx,[si] ! dh = Drive head, dl = $80 ie HD drive 0 + push si ! Save SI on read. + if mbrkey + test dl,#$80 + jz do_CHS + endif + int $13 + jc do_CHS + cmp bx,#$AA55 + jnz do_CHS else - mov di,#6 ! Max retries, int list says 3 ... double it + mov dx,[si] ! dh = Drive head, dl = $80 ie HD drive 0 + push si ! Save SI + endif + mov bx,#disk_address + mov ax,[si+8] + mov [bx],ax + mov ax,[si+10] + mov [bx+2],ax + mov si,#disk_packet + mov ah,#$42 + int $13 + pop si + jc retry_error + j sector_loaded +disk_packet: + .byte $10 + .byte 0 + .word 1 + .word $7C00 + .word 0 +disk_address: + .long 0 + .long 0 + + if useCHS +do_CHS: + pop si + endif + endif + +if useCHS mov dx,[si] ! dh = Drive head, dl = $80 ie HD drive 0 mov cx,[si+2] ! cx = Sector & head encoded for int $13 ! bx is correct at $7C00 - endif -retry: - movb [$7DFE],#0 ! Clear magic for dosemu + mov ax,#$0201 ! Read 1 sector int $13 ! Disk read. jnc sector_loaded +endif ! Error, reset and retry +retry_error: xor ax,ax int $13 ! Disk reset @@ -125,11 +204,19 @@ retry: sector_loaded: mov di,#$7DFE ! End of sector loaded cmp [di],#$AA55 ! Check for magic - jnz bad_boot ! No? Try next partition. + if diskman + jnz bad_boot ! Can't try again, two places to return to. + else + jnz try_next_part ! No? Try next partition. + endif mov bp,si ! LILO says some BBs use bp rather than si jmpi #$7C00,#0 ! Go! + else + mov si,#no_bootpart ! Message & boot + endif !(linear|useCHS) + ! Fatal errors ........... if mbrkey bad_boot: @@ -138,9 +225,7 @@ no_boot: ! SI now has pointer to error message call puts mov si,#crlf call puts -tick: - call key_pause - j tick + j key_pause else @@ -169,36 +254,32 @@ press_end: endif no_bootpart: - .asciz "No active partition" + .asciz "Bad partition" disk_read_error: - .asciz "Disk read error" - -!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -! Instead of loading using the CHS data in the ptbl use the linear addr -! - if linear -linearise: - mov di,#6 ! Max retries, int list says 3 ... double it - mov dx,[si] ! dh = Drive head, dl = $80 ie HD drive 0 - mov cx,[si+2] ! cx = Sector & head encoded for int $13 - ! bx is correct at $7C00 - - fail! Todo ... - ret - endif + .asciz "Read error" !-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ! Choose the partition based on a pressed key ... if mbrkey +key_wait: + mov si,#Prompt + call puts + call wait_key + jnz key_pause + + mov si,#Unprompt ! Nothing has happened, return. + call puts + ret + key_pause: mov si,#Pause call puts - j wait_key -key_wait: - mov si,#Prompt - call puts +key_tick: + call wait_key + jz key_tick + j Got_key wait_key: mov di,#19 ! Wait for 18-19 ticks @@ -206,7 +287,7 @@ wait_key: next_loop: mov ah,#1 int $16 - jnz Got_key + jnz done_wait mov ah,#0 int $1A ! Get current tick cmp dx,si ! If changed DEC our counter. @@ -215,43 +296,39 @@ next_loop: dec di jnz next_loop - mov si,#Unprompt ! Nothing has happened, return. - call puts - -bad_key: +done_wait: ret Got_key: mov ah,#0 ! Clean the kbd buffer. int $16 + cmp al,#0x20 + jz key_tick - cmp al,#$20 - jz key_pause ! Recursion !? - + push ax mov Showkey,al mov si,#Showkey call puts - mov al,Showkey + pop ax ! ... Now we use our key ... ! 0 => Floppy ! 1 .. 4 => Hard disk partition. - mov di,#-1 - cmp al,#$20 - jz next_loop + if useCHS + cmp al,#'F + jz is_floppy + cmp al,#'f + jz is_floppy + endif - and ax,#0xF + cmp al,#'1 + jb key_pause + cmp al,#'4 + ja key_pause - jnz not_floppy - mov si,#floppy_part - br found_active - -not_floppy: + and ax,#0x7 dec ax - test ax,#0xC - jnz bad_key - mov cl,#4 shl ax,cl add ax,#partition_start @@ -259,8 +336,18 @@ not_floppy: ! Set active flag for disk interrupt. or byte [si],#$80 + br found_active + if useCHS +is_floppy: + mov si,#floppy_part br found_active + endif + + if message +disp_message: + mov si,#Banner + endif puts: lodsb @@ -276,11 +363,15 @@ EOS: ret Prompt: - .asciz "\rMBR 0-4: " + .asciz "\rMBR: " Unprompt: - .asciz "\r \r" + .asciz "\r \r" Pause: - .asciz "\rMBR 0-4> " + if useCHS + .asciz "\rMBR F1234> " + else + .asciz "\rMBR 1234> " + endif Showkey: .ascii " " crlf: @@ -291,33 +382,6 @@ floppy_part: endif !-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -! - if message -disp_message: - mov si,#Banner - - if mbrkey - br puts - else - -puts: - lodsb - cmp al,#0 - jz .EOS - push bx - mov bx,#7 - mov ah,#$E ! Can't use $13 cause that's AT+ only! - int $10 - pop bx - jmp puts -.EOS: - ret - endif -export Banner -Banner: - .asciz "" - endif -!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ! This is the pre-boot loader it uses CHS but that's ok for track 0 ! if preboot @@ -372,7 +436,34 @@ pre_boot_table: endif !-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +! + if message&~mbrkey +disp_message: + mov si,#Banner + +puts: + lodsb + cmp al,#0 + jz .EOS + push bx + mov bx,#7 + mov ah,#$E ! Can't use $13 cause that's AT+ only! + int $10 + pop bx + jmp puts +.EOS: + ret + endif + + if message +export Banner +Banner: + .blkb 16 ! 16 bytes for the message at least. + endif + +!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ! Now make sure this isn't too big! +end_of_code: if *>table_start fail! Partition table overlaps endif @@ -380,29 +471,43 @@ pre_boot_table: !-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ! The diskman magic number and empty DM partitions. if diskman - org ORGADDR+0xFC + org table_start public diskman_magic diskman_magic: .word 0xAA55 .blkb 12*partition_size-1 - .byte 0 endif !-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -! And finally a copyright message if there's room. +! And a copyright message if there's room. + if copyright if *<ORGADDR+0x180 org ORGADDR+0x180 .asciz "ELKS MBR " .asciz "Robert de Bath," .asciz "Copyright " -.asciz "1996-2002. " +.asciz "1996-2003. " org partition_start-1 .byte 0xFF endif + endif + +!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- +! Clear the sector to the bottom of the partition table. + if markptab + if *<partition_start-1 + org partition_start-1 + .byte 0xFF + endif + endif if use512 org ORGADDR+0x1FE .word 0xAA55 endif + if 1&~(useCHS|linear|preboot) + fail! Errm, you can't boot anything without 'linear' or 'useCHS' + endif + !THE END |