325 lines
6.2 KiB
NASM
325 lines
6.2 KiB
NASM
org 0x700
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cseg equ 0x0
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jmp init
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%include "bpb.inc"
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%include "farptr.inc"
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; dflags bitfields
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DRVLOG equ 0x01 ; bit 0 (1) - drive logged in (see drvnum)
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DRVRST equ 0x02 ; bit 1 (2) - controller configured
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DRVEXT equ 0x04 ; bit 2 (4) - EBIOS supported
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DIRTY equ 0x08 ; bit 3 (8) - dskbuf dirty
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; initial setup for disk i/o
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; copy previously set DPT to our data area
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dinit xor ax, ax
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mov es, ax
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les bx, [es:4*0x1E]
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mov dx, dpt
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mov cx, 11
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call lodfar
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; set interrupt vector
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mov es, cx
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mov word [es:4*0x1E], dpt
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mov word [es:4*0x1E+2], ds
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ret
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align 16
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; IBM Interrupt Sharing Protocol structure
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i13isp jmp short int13i
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dw 0,0xFFFF
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dw 0x424B
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db 0
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iret
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align 16
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; Entry point when user program calls int13h
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; TODO: flush buffer and log out drive
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int13i call int13
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iret
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; Wrapper around int 13h
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int13 pushf
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call far [i13isp+2]
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; TODO: on error: reset & retry
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; TODO: record errors
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; TODO: multi-track reading
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; TODO: handle DMA boundaries
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ret
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; get drive parameters
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; read BIOS int13h/AH=8 values
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; DPT data gets copied over our dpt
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; CHS data gets inserted into our bpb
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getprm test byte [dskflag], 4
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jnz .ret
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; do the query
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mov ah, 8
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mov dl, [biosnum]
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call int13
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; bail out if error
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jc .ret
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; ignore CHS values if odd
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test cl, cl
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jz .nochs
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; get and store sector number
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and cx, 0x3F
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mov word [bpb+BPBSPT], cx
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; get and store number of heads
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xchg dl, dh
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and dx, 0xFF
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inc dx
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mov [bpb+BPBNOS], dx
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; test if DPT ptr is non-zero
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.nochs mov ax, es
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or ax, di
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test ax, ax
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jz .ret
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; copy BIOS dpt table over ours
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mov dx, dpt
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mov bx, di
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mov cx, 11
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call lodfar
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.ret ret
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; select a drive for io
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; IN dl drive number
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; dont do anything if drive already selected
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select cmp dl, [drvnum]
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je logfdd.ret
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; clear out current contents
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push dx
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call flush
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mov ax, 0xFFFF
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mov [dskseek], ax
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mov [dskseek+2], ax
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mov byte [dskflag], 0
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pop dx
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; set current drive number
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mov [dsknum], dl
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; fork off if hdd
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cmp dl, 2
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jnc loghdd
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logfdd mov [biosnum], dl
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; assume some default values
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xor ax, ax
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mov word [bpb+BPBHS], ax
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mov word [bpb+BPBHS+2], ax
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mov word [bpb+BPBNOS], 2 ; 5 1/4" 360kB
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mov word [bpb+BPBSPT], 9
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; reset dpt to defaults
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call getprm
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; load boot sector
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xor ax, ax
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xor dx, dx
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call mapabs
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; copy bios parameter block
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; TODO: guess from first byte of FAT if BPB invalid
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call rstseg
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mov si, dskbuf+BPBOFF
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mov di, bpb
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mov cx, BPBSIZ
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rep movsb
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; copy SPT to DPT
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mov al, [bpb+BPBSPT]
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mov [dpt+4], al
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.ret ret
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loghdd sub dl, 2
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cmp dl, 4
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jnc logerr
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push dx
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mov dl, 0x80
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mov byte [biosnum], dl
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; test for ebios extensions
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mov ah, 0x41
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mov bx, 0x55AA
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call int13
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sbb bx, 0xAA55
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jnz .chs
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; enable ebios and assume controller is configured
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or byte [dflags], DRVCTL | DRVEXT
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; get chs data (needed or we cant load vbr)
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.chs call getprm
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; read mbr
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xor ax, ax
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xor dx, dx
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call mapabs
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; get partition number
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pop bx
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xor bh, bh
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mov cl, 4
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sal bx, cl
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; bail out if no partition
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cmp byte [dskbuf+0x1be+bx+4], 0
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je logerr
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; load partition offset
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mov ax, [dskbuf+0x1be+bx+8]
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mov dx, [dskbuf+0x1be+bx+8+2]
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; save to to stack
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push dx
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push ax
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; load vbr
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call mapabs
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; copy bpb
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mov si, dskbuf+BPBOFF
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mov di, bpb
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mov cx, BPBSIZ
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rep movsb
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; fix CHS data
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call getprm
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; fix partition offset
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pop word [bpb+BPBHS]
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pop word [bpb+BPBHS+2]
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;pop [bpb+BPBNOS]
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;pop [bpb+BPBSPT]
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ret
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logerr stc
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ret
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; map sector into dskbuf
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; skip doing a read if sector number matches
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; IN dx:ax absolute sector number
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map cmp ax, [drvseek]
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jne .do
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cmp dx, [drvseek+2]
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jne .do
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ret
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; flush previous contents
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.do push ax
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push dx
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call flush
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pop dx
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pop ax
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; set sector number
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mov [drvseek], ax
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mov [drvseek+2], dx
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; issue read cmd
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mov ch, 2
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jmp diskio
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; mark dskbuf as containing unwritten changes
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dirty or word [cs:dflags], DIRTY
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l002 ret
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; flush buffer if dirty
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flush test word [cs:dflags], DIRTY
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jz l002
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; issue write cmd
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mov ch, 3
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; Do disk I/O
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; IN ch 2 = read
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; 3 = write
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; Sector number is read from [drvseek]
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diskio mov cl, 1 ; read len
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; DS := ES := CS
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call rstseg
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; check if ebios supported
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test word [dflags], DRVEXT
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jz .noext
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; set up regs for ebios call
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mov ax, cx
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or ah, 0x40
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mov si, dap
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jmp .do
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; check if we can skip controller reset
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.noext test word [dflags], DRVRST
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jnz .norst
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; do controller reset
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mov dl, [biosnum]
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mov ah, 0
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call int13
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or word [dflags], DRVRST
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; put linear sector num into dx:ax
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.norst mov ax, [drvseek]
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mov dx, [drvseek+2]
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; dx:ax = linear count
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div word [drvspc]
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; TODO: is it possible to get an overflow here?
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xchg ax, dx
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; dx = cylinder, ax = head * spt + sector
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div byte [drvspt]
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; dx = cylinder, al = head, ah = sector
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xchg dl, dh
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ror dl, 1
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ror dl, 1
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or dl, ah
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inc dx
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; al: head number
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; dh bit 0-7: cylinder bits 0-7
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; dl bit 0-5: sector bits 0-5
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; dl bit 6-7: cylinder bits 8-9
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; shuffle values around for bios
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xchg ax, cx
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xchg cx, dx
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xchg dh, dl
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mov bx, dskbuf
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.do mov dl, [biosnum]
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; ah: subfunction selected via cx previously
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; al: 1 = reading 1 sector
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; cx: sector and cylinder number
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; dh: head number
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; dl: drive number
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; bx: offset to disk buffer
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call int13
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jc .err
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; clear dirty flag on success
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and word [dflags], ~DIRTY
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clc
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ret
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; assume controller is misconfigured
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.err and word [dflags], ~DRVRST
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; exit with carry flag set
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stc
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ret
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init mov ax, cs
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; boot failure if loaded wrong
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cmp ax, cseg
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je $+4
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int 0x18
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halt hlt
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jmp halt
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dap db 0x10, 0
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dw 1
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dw dskbuf, cseg
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drvseek dw 0,0,0,0
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; bit 0 (1) - drive logged in (see drvnum)
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; bit 1 (2) - controller configured
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; bit 2 (4) - EBIOS supported
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; bit 3 (8) - dskbuf dirty
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dflags dw 0
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section .bss
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; drive currently logged in
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drvnum resb 1
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; number, just for bios
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biosnum resb 1
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; DPT tables for 4 floppy drives
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dpt resb 4*14
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; Information for logged in drive
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drvss resb 1 ; sector size, 2^(7+n) bytes
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drvcs resb 1 ; cluster size, 2^(7+n) bytes
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alignb 4
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drvspt resb 2 ; sectors per track
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drvspc resb 2 ; sectors per cylinder
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drvoff resb 4 ; partition offset
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drvend resb 4 ; first sector after the partition
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drvfat resb 4 ; offset to fat table
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drvrd resb 4 ; offset of root directory
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drvcla resb 4 ; offset to cluster area
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drvfn resb 2 ; sectors per fat table
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; disk buffer for I/O operations
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alignb 2
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dskbuf resb 1024
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