Workstate on disk I/O rework
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79a86bad49
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19
boot/mbr.asm
19
boot/mbr.asm
@ -1,6 +1,7 @@
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cpu 8086
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%define seg 0x060
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%define seg 0
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%define off 0x700
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org 0x7C00 - (seg << 4)
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@ -16,24 +17,12 @@ init: cli
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.retry: mov ax, 0x0208
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mov cx, 2
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mov dh, 0
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mov bx, 0x100
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mov bx, off
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int 0x13
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jc .retry
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xor di, di
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mov ax, 0x18CD
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stosw
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int 0x12
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mov cl, 6
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shl ax, cl
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stosw
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mov al, 2
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stosb
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mov ax, 0x18CD
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stosw
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jmp seg:0x100
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jmp seg:off
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times (0x1BE - ($-$$)) db 0
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151
src/@rdos.asm
151
src/@rdos.asm
@ -1,15 +1,15 @@
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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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; drive actually selected for I/O
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dsknum db 0xFF
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dap db 0x10, 0
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dw 1
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dapbuf dw dskbuf, 0
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dskseek dw 0,0,0,0
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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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@ -23,8 +23,6 @@ dinit xor ax, ax
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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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; set segment addr in DAP
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mov [dapbuf+2], cs
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ret
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align 16
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@ -36,6 +34,8 @@ i13isp jmp short int13i
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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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@ -86,7 +86,7 @@ getprm test byte [dskflag], 4
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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, [dsknum]
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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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@ -140,7 +140,7 @@ loghdd sub dl, 2
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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 [dskflag], (2+4)
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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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@ -181,74 +181,68 @@ logerr stc
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ret
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; map sector into dskbuf
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; sector number from partition start
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; IN dx:ax sector number
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map add ax, [bpb+BPBHS]
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add dx, [bpb+BPBHS+2]
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; absolute sector count
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; skip doing a read if sector number matches
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; IN dx:ax sector number
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mapabs cmp ax, [dskseek]
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jne l003
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cmp dx, [dskseek+2]
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je l002
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; flush and read other sector
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l003 push ax
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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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; store the sector number
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mov [dskseek], ax
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mov [dskseek+2], dx
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jmp _read
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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 byte [cs:dskflag], 1 ; dirty
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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 byte [cs:dskflag], 1
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flush test word [cs:dflags], DIRTY
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jz l002
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; low level read and write
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; call again to retry, no input registers
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; read or write is configured in cx
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_write mov ch, 3
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db 0x3D ; cmp ax, imm16: causes next 2 bytes to be skipped
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_read mov ch, 2
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mov cl, 1 ; read len
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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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mov ax, cs
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mov ds, ax
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mov es, ax
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call rstseg
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; check if ebios supported
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test byte [dskflag], 4
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jz .l00
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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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.l00 test byte [dskflag], 2
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jnz .l01
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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 byte [dskflag], 2
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; put sectors per cylinder into bx
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.l01 mov ax, [bpb+BPBSPT]
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mul word [bpb+BPBNOS]
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mov bx, ax
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or word [dflags], DRVRST
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; put linear sector num into dx:ax
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mov ax, [dskseek]
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mov dx, [dskseek+2]
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; dx:ax = linear count, bx = sectors / cylinder
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div bx
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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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mov bl, [bpb+BPBSPT]
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div byte bl
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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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@ -274,34 +268,57 @@ _read mov ch, 2
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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 byte [dskflag], 0xFE
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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 byte [dskflag], 0xFD
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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, 0x0e38
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int 0x10
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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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section .bss
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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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; bios drive we end up using
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biosnum resb 1
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; bit 0 (1) - dirty flag for dskbuf
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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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dskflag resb 1
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; bit 3 (8) - dskbuf dirty
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dflags dw 0
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dpt resb 11
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section .bss
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bpb resb BPBSIZ
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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 512
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dskbuf resb 1024
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