diff options
Diffstat (limited to 'bootblocks/bootlist.s')
| -rw-r--r-- | bootblocks/bootlist.s | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/bootblocks/bootlist.s b/bootblocks/bootlist.s new file mode 100644 index 0000000..889842a --- /dev/null +++ b/bootblocks/bootlist.s @@ -0,0 +1,256 @@ +! This bootsector is modified by the installer to have a list of sectors at +! offset 256. + +! Table format is a list of dwords. Each dword has a partition offest in +! the low 24 bits and a count in the high. +! +! Prob better to make it: HH DD MM LL rather than DD HH MM LL +! as this matches the BIOS better +! +! Note: +! Stack top is at abs location 64k. +! + +BOOTSEG = 0x07c0 +LOADSEG = 0x07e0 ! Just after boot sector. + +public linear +linear = 1 ! Is linear processing done ? + +public floppy +floppy = 0 *linear ! Allow for floppy drive ? +public reloc +reloc = 1 *linear ! Auto configure of bootpart. + +macro locn + if *-start>?1 + fail + endif + .blkb ?1 + start-* +mend + +use16 +entry start + +org $7b00 + +! temporary space + +n_cyl: .blkw 1 +n_secs: .blkw 1 +t_drive: .blkb 1 +t_sector: .blkb 1 +t_secs: .blkw 1 + +org $7c00 +start: + j code + +runit: + jmpi 0,0 ! This instruction is altered by the installer + +public execaddr ! Via this label. +execaddr = *-4 + +public bootpart +bootpart: + .data4 0x80000011 +code: + + if reloc + mov cx,[si+8] ! Fetch the linear address of part from DS:SI + mov dh,[si+10] ! DL is drive number + xchg dl,dh ! Into normal form. + endif + + xor ax,ax + mov ds,ax + mov ss,ax + mov sp,ax + + if reloc + mov [bootpart],cx + mov [bootpart+2],dx + endif + +! ASSUME ds=ss= 0 (cs should also be zero) + + mov ax,#LOADSEG + mov es,ax + + mov si,#table +load_addrs: + cld + + if linear + lodsw + mov cx,ax + add cx,[bootpart] + lodsw + mov dx,[bootpart+2] + adc dl,al + mov al,ah + else + lodsw + mov cx,ax + lodsw + mov dx,ax + lodsb + endif + + test al,al + jz runit + +loadem: + xor bx,bx + push ax + call cread + jc failed + pop ax + mov cl,#5 + sal ax,cl + mov bx,es + add ax,bx + mov es,ax + j load_addrs + +! Humm, something goes wrong, not much we can do ... +! Let`s squeak then try again +failed: + mov ax,#$0E45 + mov bx,#7 + int $10 + pop ax + + j loadem + +cread: + ! This function is like BIOS 1302 but it`s linear. + ! It's taken, almost, intact from LILO. + + ! DH is drive, DL:CX is linear address, AL is count. + ! ES:BX is load address, beware of DMA limitations + + ! All registers except AX and flags are preserved. + + mov t_secs,al ! save number of sectors +lnread: push cx ! keep linear address + push dx + xchg dl,dh + + if linear + if floppy + test dl,#0x80 ! Floppy is physical only. + jz lrd + endif + + push bx ! BX is used as scratch + push cx ! LSW + push dx ! MSW with drive + mov ah,#8 ! get drive geometry (do not clobber ES:DI) + push es + push di + int 0x13 + pop di + pop es + mov bl,dh ! BL <- #heads + pop dx ! get MSW + + jnc int_ok ! error -> quit + + pop cx ! discard stack contents + pop bx + pop dx + pop cx + ret ! (carry is already set) +int_ok: + mov t_drive,dl ! save drive + mov dl,dh ! linear address into DX:AX + xor dh,dh + mov bh,dh ! (clear BH too) + pop ax + push cx ! compute #cyls-1 + xchg ch,cl + rol ch,1 + rol ch,1 + and ch,#3 + mov n_cyl,cx ! save #cyls-1 + pop cx + and cx,#0x3f ! CX <- #secs + mov n_secs,cx + div cx ! AX <- track, DX <- sector + inc dl + mov t_sector,dl + xor dx,dx ! divide by #heads + inc bx + div bx ! AX <- cylinder, DX <- head + mov dh,dl ! set up DX (head:drive) + mov dl,t_drive + cmp ax,n_cyl ! valid cylinder number ? + ja linerr3 ! no -> error + xchg ah,al ! build cylinder number + ror al,1 + ror al,1 + or al,t_sector + mov cx,ax + pop bx ! restore BX + and ax,#0x3f ! read beyond end of track ? + add ax,t_secs + cmp ax,n_secs + jna intrk ! no -> go on + mov al,n_secs ! read to end of track + sub al,t_sector + inc al + jmp lrd ! read it +intrk: mov al,t_secs ! read all sectors + + endif + +lrd: push ax ! save AX and BX + push bx + + mov ah,#2 ! + int 0x13 ! read sectors + + pop bx ! restore AX and BX and the linear address + pop ax + pop dx + pop cx + + if linear + + jc linerr ! error -> quit + sub t_secs,al ! adjust sector count + jz lindone ! zero -> done + xor ah,ah ! increase linear address + add cx,ax + adc dh,#0 + xchg ah,al ! move BX + add ah,ah + add bx,ax + jc interr ! crossing segment boundaries -> error + br lnread ! process remaining sectors + +linerr3:pop bx ! pop BX and linear address + pop dx + pop cx +interr: xor ax,ax ! zero indicates internal error + + else + jnc lindone + endif + +linerr: stc ! error + ret +lindone:clc ! no error + ret ! done + + +!-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- + +public table +table: +! .long 0x80000012 +! .byte 1 +! .long 0x07e00000 +! .byte 0 |