Implement map-like sector access for floppy drives
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@ -31,8 +31,17 @@ print_banner: mov si, banner
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call dskrst
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mov bx, testfcb
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call fcbfst
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mov dl, [defdrv]
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call logdrv
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xor ax, ax
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xor dx, dx
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call maprd
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inc word [dskbuf+0x82]
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call dirty
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call flush
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hlt: hlt
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jmp hlt
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183
kernel/drive.asm
183
kernel/drive.asm
@ -1,10 +1,25 @@
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; code for disk i/o
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; from outside, only the following methods are meant to be called:
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; - logdrv: select drive DL to operate on
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; - map*: map sector DX:AX into dskbuf
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; - dirty: inform that dskbuf has been written to
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; access is done by accessing dskbuf directly
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section .bss
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; drive actually selected for I/O
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dsknum: resb 1
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; bios drive we end up using
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biosnum: resb 1
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; current sector number
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; absolute, ignores partition
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dskseek: resd 1
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; bit 0 - dirty flag for dskbuf
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dskflag: resb 1
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; disk buffer for I/O operations
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dskbuf: resb 512
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@ -13,69 +28,6 @@ bpb: resb BPBSIZ4
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section .text
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ret: ret
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; Convert drive number into DL for int 13h
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; A=0, B=1, C=0x80
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; IN dl dos drive number
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; OUT dl bios drive number
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getdl: cmp dl, 2
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jc ret
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mov dl, 0x80
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ret
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; Ask BIOS for drive parameters
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; IN dl dos drive number
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; OUT CX,DH chs data
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; ES:DI DPT if floppy
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qrychs: mov ah, 8
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les di, [0x1E*4]
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int 0x13
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jc .defs
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test cl, cl
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jz .defs
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ret
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.defs: mov cx, 0x2709 ; max track = 39, max sec = 9
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mov dh, 1 ; 2 heads
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ret
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; select drive
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; IN dl drive number
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dsksel: cmp dl, byte [dsknum]
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je ret
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call dskrst
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call getdl
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push dx
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call qrychs
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; store CHS data in BPB
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xor ax, ax
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mov al, cl
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mov [bpb+BPBSPT], ax
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mov al, dh
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inc ax
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mov [bpb+BPBNOS], ax
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; get dpt from bios if not hdd
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pop dx
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test dl, 0x80
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jnz .nodpt
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push dx
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mov dx, dpt
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mov bx, di
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mov cx, DPTSIZE
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call lod
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mov ax, [bpb+BPBSPT]
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mov [dpt+DPTSPT], al
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pop dx
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.nodpt:
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ret
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dskrst: call flush
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mov ax, 0xFFFF
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mov [dsknum], al
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@ -83,5 +35,108 @@ dskrst: call flush
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mov [dskseek+2], ax
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ret
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; log in drive
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; currently only supports 18 sectors 2 heads floppies
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; IN dl drive number
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logdrv: mov [biosnum], dl
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xor ax, ax
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xor dx, dx
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call read
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; copy bios parameter block
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lea si, [dskbuf+BPBOFF]
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mov di, bpb
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mov cx, BPBSIZ4
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rep movsb
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; make sure partition offset is force zero
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xor ax, ax
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mov [bpb+BPBHS], ax
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mov [bpb+BPBHS+2], ax
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ret
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calchs: mov bx, (18*2)
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; dx:ax = linear count, bx = sectors / cylinder
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div bx
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xchg ax, dx
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; dx = cylinder, ax = head * spt + sector
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mov bl, 18
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div byte bl
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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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mov cx, dx
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mov dh, al
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mov dl, [biosnum]
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mov bx, dskbuf
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ret
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mapclu: ; counting from begin of cluster area
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mov bx, [bpb+BPBRDE]
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mov cl, 4
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shr bx, cl ; 32 bytes per entry
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add ax, bx
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adc dx, 0
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maprd: ; counting from beginning of dir
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; add fat table sizes
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xor ch, ch
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mov cl, byte [bpb+BPBFN]
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.loop: add ax, [bpb+BPBFS]
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adc dx, 0
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loop .loop
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mapfat: ; counting from beginning of FAT
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; add reserved sector count
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add ax, [bpb+BPBRSC]
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adc dx, 0
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map: ; count from partition start
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;add ax, [BPBHS]
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;add dx, [BPBHS+2]
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; absolute sector count
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mapabs: call read
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ret
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; hard read, absolute disk offset
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; TODO: retries on error
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; IN dx:ax
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read: ; flush previous data if necessary
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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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; do the actual read
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; TODO: error handling & retries
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call calchs
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mov ax, 0x0201
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int 0x13
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ret
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; mark dskbuf as containing unwritten changes
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dirty: or byte [dskflag], 1 ; dirty
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ret
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; flush buffer if dirty
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flush: ret
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flush: test byte [dskflag], 1
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jz .ret
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; load sector number
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mov ax, [dskseek]
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mov dx, [dskseek+2]
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; do the write
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; TODO: error handling & retries
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call calchs
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mov ax, 0x0301
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int 0x13
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; remove dirty flag
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and byte [dskflag], 0xFE
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.ret: ret
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@ -17,7 +17,7 @@ setdrv: mov dl, [es:bx+fcb.drive] ; A=1
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mov [es:bx+fcb.drive], dl ; A=1
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; now set as current i/o drive
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.nofix: dec dl ; A=0 for dsksel
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jmp dsksel
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jmp logdrv
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; FCB open
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fcbopn: ; call fcbfst
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