To disk.asm we will add first entry and next entry. These functions return directory entries. The main routine is next entry. First entry clears a couple variables then drops into next entry.
;-------------------------------------------------------
; Get first directory match
; Input:
; None
; Output:
; ES:BX Points to directory entry
;-------------------------------------------------------
dskfirstentry:
mov [diroffset], word 0 ; Clear offset for new read
mov [ldrsectorload], word 0
; drops into next entry
;-------------------------------------------------------
; Get next directory match
; Input:
; None
; Output:
; ES:BX Points to directory entry
;-------------------------------------------------------
dsknextentry:
push ax
push cx
push dx
push di
xor bx, bx ; es:bx = scratch area
mov es, bx
dsknextentrynext:
cmp [dircurrent], word 0 ; check if root directory
jnz dsknextentryfile ; if not process as file
mov ax, 32 ; Calc size of root
mul word [rootdirents]
mov bx,[bytespersec]
add ax, bx
cmp [diroffset], ax ; check if we are past the end
jge dsknextentryerror ; we have reached the end
jmp dsknextentrydone
dsknextentryfile:
; *** this needs to be written when we can change directory ***
; calulate which cluster to read
; crawl fat for current cluster
; calulate which sector of cluster
dsknextentrydone:
mov ax, [diroffset] ; read sector = diroffset / BYTES PER SECTOR
xor dx, dx
div word [bytespersec]
push dx ; dx should equal index into sector
add ax, [root] ; add directory base
cmp [ldrsectorload], ax ; Check if this sector is already in scratch
jz dsknextentryskprd ; If it is don't load it again
mov [ldrsectorload], ax ; Set current loaded FAT sector
mov bx, 00500h
xor dx, dx
call calcchs ; Calc chs
jc dsknextentryerrorpop
call readsec ; read sector
jc dsknextentryerrorpop
dsknextentryskprd:
pop bx ; restore index
add bx, 00500h
cmp [es:bx], byte 0 ; check if entry is blank
jz dsknextentryerror ; if so we reached the end
mov di, bx
call dskcmpmatch ; see if it matches our match string
jnc dsknextentryexit
add [diroffset], word 32 ; point to next dir entry
jmp dsknextentrynext
dsknextentryexit:
add [diroffset], word 32 ; point to next dir entry
pop di
pop dx
pop cx
pop ax
clc
ret
dsknextentryerrorpop:
pop dx
dsknextentryerror:
pop di
pop dx
pop cx
pop ax
stc
ret
Next we will add match blank this creates a blank match string of all question marks to compare to.
;-------------------------------------------------------
; Build blank match string
; Input:
; es:di = Buffer
; Output:
; matchname = Match Name
;-------------------------------------------------------
dskmatchblank:
push cx
push si
mov cx, 11
mov si, matchname
dskmatchblanknext:
mov [ds:si], byte '?'
inc si
loop dskmatchblanknext
pop si
pop cx
ret
matchname: db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
After that we will add compare match. this will match a directory entry to our generated match name.
;-------------------------------------------------------
; Compare match string
; Input:
; es:di = Directory entry
; Output:
; Carry Set = not match
; Carry Clear = match
;-------------------------------------------------------
dskcmpmatch:
mov si, matchname
mov cx, 00Bh
dskcmpmatchnext:
mov al, [si]
inc si
cmp al, '?'
jz dskcmpmatchauto
cmp [es:di], al
jnz dskcmpmatchfail
dskcmpmatchauto:
inc di
loop dskcmpmatchnext
clc
ret
dskcmpmatchfail:
stc
ret
Then we will finish it off with a couple of variables.
diroffset: dw 0 dircurrent: dw 0
;=======================================================
; Disk - disk.asm
; -----------------------------------------------------
; Written in NASM
; Written by Marcus Kelly
; -----------------------------------------------------
; Copyright 2021 Marcus Kelly
;=======================================================
;-------------------------------------------------------
; Convert current drive to drive letter
; Input:
; None
; Output:
; AL = Drive Letter
;-------------------------------------------------------
dskdriveletter:
mov al, [drivenumber]
test al, byte 080h
jz dskdriveletternoadj
sub al, 078h
dskdriveletternoadj:
add al, 'A'
ret
;-------------------------------------------------------
; Get first directory match
; Input:
; None
; Output:
; ES:BX Points to directory entry
;-------------------------------------------------------
dskfirstentry:
mov [diroffset], word 0 ; Clear offset for new read
mov [ldrsectorload], word 0
; drops into next entry
;-------------------------------------------------------
; Get next directory match
; Input:
; None
; Output:
; ES:BX Points to directory entry
;-------------------------------------------------------
dsknextentry:
push ax
push cx
push dx
push di
xor bx, bx ; es:bx = scratch area
mov es, bx
dsknextentrynext:
cmp [dircurrent], word 0 ; check if root directory
jnz dsknextentryfile ; if not process as file
mov ax, 32 ; Calc size of root
mul word [rootdirents]
mov bx,[bytespersec]
add ax, bx
cmp [diroffset], ax ; check if we are past the end
jge dsknextentryerror ; we have reached the end
jmp dsknextentrydone
dsknextentryfile:
; *** this needs to be written when we can change directory ***
; calulate which cluster to read
; crawl fat for current cluster
; calulate which sector of cluster
dsknextentrydone:
mov ax, [diroffset] ; read sector = diroffset / BYTES PER SECTOR
xor dx, dx
div word [bytespersec]
push dx ; dx should equal index into sector
add ax, [root] ; add directory base
cmp [ldrsectorload], ax ; Check if this sector is already in scratch
jz dsknextentryskprd ; If it is don't load it again
mov [ldrsectorload], ax ; Set current loaded FAT sector
mov bx, 00500h
xor dx, dx
call calcchs ; Calc chs
jc dsknextentryerrorpop
call readsec ; read sector
jc dsknextentryerrorpop
dsknextentryskprd:
pop bx ; restore index
add bx, 00500h
cmp [es:bx], byte 0 ; check if entry is blank
jz dsknextentryerror ; if so we reached the end
mov di, bx
call dskcmpmatch ; see if it matches our match string
jnc dsknextentryexit
add [diroffset], word 32 ; point to next dir entry
jmp dsknextentrynext
dsknextentryexit:
add [diroffset], word 32 ; point to next dir entry
pop di
pop dx
pop cx
pop ax
clc
ret
dsknextentryerrorpop:
pop dx
dsknextentryerror:
pop di
pop dx
pop cx
pop ax
stc
ret
;-------------------------------------------------------
; Build blank match string
; Input:
; es:di = Buffer
; Output:
; matchname = Match Name
;-------------------------------------------------------
dskmatchblank:
push cx
push si
mov cx, 11
mov si, matchname
dskmatchblanknext:
mov [ds:si], byte '?'
inc si
loop dskmatchblanknext
pop si
pop cx
ret
matchname: db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
;-------------------------------------------------------
; Compare match string
; Input:
; es:di = Directory entry
; Output:
; Carry Set = not match
; Carry Clear = match
;-------------------------------------------------------
dskcmpmatch:
mov si, matchname
mov cx, 00Bh
dskcmpmatchnext:
mov al, [si]
inc si
cmp al, '?'
jz dskcmpmatchauto
cmp [es:di], al
jnz dskcmpmatchfail
dskcmpmatchauto:
inc di
loop dskcmpmatchnext
clc
ret
dskcmpmatchfail:
stc
ret
diroffset: dw 0
dircurrent: dw 0
In demoos.asm we will add a new command string
dirstr: db "DIR", 0
Now we will add a veriable to keep track of the sector we are on in the directory.
seccount: dw 0
Then we will add the directory list code
;-------------------------------------------------------
; Directory List
; Input:
; None
; Output:
; None
;-------------------------------------------------------
dir:
push ax ; Save registers
push bx
push cx
push dx
push es
call vol ; Print volume information
call crlf
call dskmatchblank ; create a blank match string
call dskfirstentry ; get first entry
jc dirdone
dirnext:
mov cx, 0000Bh ; Name length
dirname:
mov ah, 002h ; Service stdout
mov dl, [es:bx] ; Get filename character
inc bx ; Point to next character
int 021h ; Print the character we got
loop dirname ; Get next character, dec cx
call crlf
call dsknextentry
jc dirdone
loop dirnext
dirdone:
pop es ; Restore registers
pop dx
pop cx
pop bx
pop ax
ret
Add the code to check if it is the DIR command to main.
mov si, dirstr ; Point to command text
call cmpcmd ; Compare
jc cmdndir ; Carry set if not equal
call dir ; Call function
jmp main ; We're done checking
cmdndir:
Then we will replace:
version: db 00Dh, 00Ah, "DEMO OS V0.13" ; Message to be printed
db 00Dh, 00Ah, '$'
with
version: db 00Dh, 00Ah, "DEMO OS V0.14" ; Message to be printed
db 00Dh, 00Ah, '$'
;=======================================================
; Demo OS - demoos.asm
; -----------------------------------------------------
; Written in NASM
; Written by Marcus Kelly
; -----------------------------------------------------
; Copyright 2021 Marcus Kelly
;=======================================================
%include "loader.asm"
start:
call intinit ; Initialize interrupts
push ds ; Save DS
mov ax, 00FFFh ; Set first MCB
mov [mcbfirst], ax ; Save first MCB
mov ds, ax
mov bx, 07000h ; Size to initialize
call meminit ; Initialize memory
pop ds ; Restore DS
call ver
main:
call crlf ; Print carriage return / line feed
mov ah, 002h ; Service standard output
call driveletter ; Print drive letter
mov dl, al
int 021h
mov dl, ':' ; Print ':'
int 021h
mov dl, '\' ; Print '\'
int 021h
mov dl, '>' ; Print '>'
int 021h
mov dl, ' ' ; Print Space
int 021h
mov ax, es
mov ah, 00Ah ; Service string input
mov dx, buffer ; Set dx to our buffer
int 021h
call crlf ; Print carriage return / line feed
mov di, buffer+2 ; Point to the string we typed
mov si, verstr ; Point to command text
call cmpcmd ; Compare
jc cmdnver ; Carry set if not equal
call ver ; Call function
jmp main ; We're done checking
cmdnver:
mov si, clsstr ; Point to command text
call cmpcmd ; Compare
jc cmdncls ; Carry set if not equal
call cls ; Call function
jmp main ; We're done checking
cmdncls:
mov si, echostr ; Point to command text
call cmpcmd ; Compare
jc cmdnecho ; Carry set if not equal
call echo ; Call function
jmp main ; We're done checking
cmdnecho:
mov si, mcbstr ; Point to command text
call cmpcmd ; Compare
jc cmdnmcb ; Carry set if not equal
call mcb ; Call function
jmp main ; We're done checking
cmdnmcb:
mov si, allocstr ; Point to command text
call cmpcmd ; Compare
jc cmdnalloc ; Carry set if not equal
call alloc ; Call function
jmp main ; We're done checking
cmdnalloc:
mov si, freestr ; Point to command text
call cmpcmd ; Compare
jc cmdnfree ; Carry set if not equal
call free ; Call function
jmp main ; We're done checking
cmdnfree:
mov si, resizestr ; Point to command text
call cmpcmd ; Compare
jc cmdnresize ; Carry set if not equal
call resize ; Call function
jmp main ; We're done checking
cmdnresize:
mov si, volstr ; Point to command text
call cmpcmd ; Compare
jc cmdnvol ; Carry set if not equal
call vol ; Call function
jmp main ; We're done checking
cmdnvol:
mov si, dirstr ; Point to command text
call cmpcmd ; Compare
jc cmdndir ; Carry set if not equal
call dir ; Call function
jmp main ; We're done checking
cmdndir:
mov ah, 009h ; Service Print String
mov dx, invalid ; Invalid command
int 021h ; Our Service
call crlf ; New line
jmp main ; Repeat forever
;-------------------------------------------------------
; Compare Command
; Input:
; DS:SI = Command String
; ES:DI = Buffer String
; Output:
; Carry set if not equal
; Carry clear if equal
;-------------------------------------------------------
cmpcmd:
push ax ; Save registers
push si
push di
cmpcmdnext:
mov al, [es:di] ; Load char from command line
inc di ; Point to next character
call toup ; Convert to uppercase
mov ah, [ds:si] ; Load char to test against
inc si ; Point to next character
cmp ah, al ; Compare both characters
jz cmpcmdnext ; If they are the same check next
dec si ; Adjust to point to last char
dec di
cmp [ds:si], byte 0 ; Our test command end should be 0
jnz cmpcmdne ; If it isn't not our command
cmp [es:di], byte ' ' ; Our input cmd might be space
jz cmpcmde ; If it is this is our command
cmp [es:di], byte 00Dh ; Our input cmd might be CR
jz cmpcmde ; If it is this is our command
jmp cmpcmdne ; Otherwise not our command
cmpcmde:
pop di ; Restore registers
pop si
pop ax
clc ; Clear carry for match
ret ; Return from subroutine
cmpcmdne:
pop di ; Restore registers
pop si
pop ax
stc ; Set carry if not a match
ret ; Return from subroutine
;-------------------------------------------------------
; Version Command
; Input:
; None
; Output:
; AX, DX are Destroyed
;-------------------------------------------------------
ver:
mov ah, 009h ; Service string output
mov dx, version ; dx is set to offset version
int 021h ; Call the service
ret
;-------------------------------------------------------
; Clear Screen Command
; Input:
; None
; Output:
; AX is Destroyed
;-------------------------------------------------------
cls:
mov ah, 00Fh ; Get video mode
int 010h
mov ah, 000h ; Set video mode
int 010h ; this automatically clears the screen
ret
;-------------------------------------------------------
; Echo Command
; Input:
; None
; Output:
; None
;-------------------------------------------------------
echo:
push ax ; Save registers
push dx
push di
xor ah, ah ; Clear upper part of ax
mov al, [buffer+1] ; Get count from buffer
mov di, buffer+2 ; Get start of buffer
add di, ax ; Add for end of buffer
mov al, '$' ; Place '$' at end for printing
mov [di], al
mov ah, 009h ; Service print string
mov dx, buffer+7 ; Get start of string to print
int 021h ; 7 to exclude echo
call crlf
pop di ; Restore regsiters
pop dx
pop ax
ret ; Return from subroutine
;-------------------------------------------------------
; Memory Control Block Command
; Input:
; None
; Output:
; AX is Destroyed
;-------------------------------------------------------
mcb:
push ax ; Save Registers
push dx
push ds
call crlf ; Print CR / LF
mov ax, [mcbfirst] ; DS = first mcb
mov ds, ax
mcbnext:
mov ax, ds ; Print arena segment
call hexwordout
mov ah, 002h
mov dl, ' ' ; Print space
int 021h
mov ah, 002h ; Print signature
mov dl, [ds:memarena.signature]
push dx ; Save signature
int 021h
mov ah, 002h
mov dl, ' ' ; Print space
int 021h
mov ax, [ds:memarena.owner] ; Print owner
call hexwordout
mov ah, 002h
mov dl, ' ' ; Print space
int 021h
mov ax, [ds:memarena.size] ; Print size
call hexwordout
mov ah, 002h
mov dl, ' ' ; Print space
int 021h
xor si, si ; Print name
mov cx, 8
mcbnextname:
mov dl, [ds:si+memarena.name] ; Read name byte
mov ah, 002h ; Print name byte
int 021h
inc si ; Increment name byte
loop mcbnextname ; Get next name byte
pop dx ; Restore signature
cmp dl, 'Z' ; Compare to end arena
jz mcbdone ; if yes were done
call memarenanext ; Get next arena
jc mcbdone ; failed were done
call crlf ; Print CR / LF for next arena
jmp mcbnext ; Next arena
mcbdone:
call crlf ; Print CR / LF
pop ds ; Restore registers
pop dx
pop ax
ret ; Return from subroutine
;-------------------------------------------------------
; Memory Allocate Command
; Input:
; Command line hex number
; Output:
; None
;-------------------------------------------------------
alloc:
push ax ; Save registers
push bx
push si
mov si, buffer+8 ; Get buffer + 8 point to hex input
call hexwordin ; Get hex input
mov bx, ax ; Allocate input size
mov ah, 048h ; Service Allocate
int 021h
jc allocerror
call crlf ; Print CR / LF
call hexwordout ; Show allocated page start
call crlf ; Print CR / LF
allocerror:
pop si ; Restore registers
pop bx
pop ax
ret ; Return from subroutine
;-------------------------------------------------------
; Memory Free Command
; Input:
; Command line hex number
; Output:
; None
;-------------------------------------------------------
free:
push ax ; Save registers
push si
push es
mov si, buffer+7 ; Get buffer + 8 point to hex input
call hexwordin ; Get hex input
mov es, ax ; Free page
mov ah, 049h ; Service Free
int 021h
jc freeerror
freeerror:
pop es
pop si ; Restore registers
pop ax
ret ; Return from subroutine
;-------------------------------------------------------
; Memory Resize Command
; Input:
; Command line hex number
; Output:
; None
;-------------------------------------------------------
resize:
push ax ; Save registers
push si
push es
mov si, buffer+9 ; Get buffer + 8 point to hex input
call hexwordin ; Get hex input
mov es, ax ; Free page
mov si, buffer+14
call hexwordin ; Get hex input
mov bx, ax
mov ah, 04Ah ; Service Resize
int 021h
jc resizeerror
resizeerror:
pop es
pop si ; Restore registers
pop ax
ret ; Return from subroutine
;-------------------------------------------------------
; Volume Info Command
; Input:
; None
; Output:
; None
;-------------------------------------------------------
vol:
push ax ; Save registers
push bx
push cx
push dx
push di
push es
; read boot sector into scratch
xor ax, ax ; Point to scratch area
mov es, ax
mov bx, 00500h
xor dx, dx ; AX = 0
call calcchs ; Calculate CHS
jc volerror
call readsec ; Read sector
jc volerror
; print data from boot sector
mov ah, 009h ; Print string
mov dx, volname
int 021h
mov ah, 002h ; drive letter
call driveletter
mov dl, al
int 021h
mov ah, 009h ; Print string
mov dx, volname2
int 021h
mov di, bx ; Print volume label
add di, 0002Bh
mov cx, 11
vollabelnext:
mov dl, [es:di]
inc di
call stdout
loop vollabelnext
mov ah, 009h ; Print string
mov dx, volserial
int 021h
mov di, bx ; Print serial first part
add di, 00029h
mov ax, [es:di]
call hexwordout
mov ah, 002h ; Print -
mov dl, '-'
int 021h
mov di, bx ; Print serial second part
add di, 027h
mov ax, [es:di]
call hexwordout
call crlf ; Print crlf
volerror:
pop es ; Restore registers
pop di
pop dx
pop cx
pop bx
pop ax
ret ; Return from subroutine
;-------------------------------------------------------
; Directory List
; Input:
; None
; Output:
; None
;-------------------------------------------------------
dir:
push ax ; Save registers
push bx
push cx
push dx
push es
call vol ; Print volume information
call crlf
call dskmatchblank ; create a blank match string
call dskfirstentry ; get first entry
jc dirdone
dirnext:
mov cx, 0000Bh ; Name length
dirname:
mov ah, 002h ; Service stdout
mov dl, [es:bx] ; Get filename character
inc bx ; Point to next character
int 021h ; Print the character we got
loop dirname ; Get next character, dec cx
call crlf
call dsknextentry
jc dirdone
loop dirnext
dirdone:
pop es ; Restore registers
pop dx
pop cx
pop bx
pop ax
ret
%include "io.asm"
%include "int.asm"
%include "mem.asm"
%include "disk.asm"
;-------------------------------------------------------
; Data Area
;-------------------------------------------------------
verstr: db "VER", 0
clsstr: db "CLS", 0
echostr: db "ECHO", 0
mcbstr: db "MCB", 0
allocstr: db "ALLOC", 0
freestr: db "FREE", 0
resizestr: db "RESIZE", 0
volstr: db "VOL", 0
dirstr: db "DIR", 0
version: db 00Dh, 00Ah, "DEMO OS V0.14" ; Message to be printed
db 00Dh, 00Ah, '$'
invalid: db 00Dh, 00Ah, "Invalid Command" ; Message to be printed
db '$'
volname: db 0x0D, 0x0A, " Volume in drive $"
volname2: db " is $"
volserial: db 0x0D, 0x0A, " Volume Serial Number is $"
buffer: db 64 ; Buffer for string input
db 0
db 0, 0, 0, 0, 0, 0, 0, 0
db 0, 0, 0, 0, 0, 0, 0, 0
db 0, 0, 0, 0, 0, 0, 0, 0
db 0, 0, 0, 0, 0, 0, 0, 0
db 0, 0, 0, 0, 0, 0, 0, 0
db 0, 0, 0, 0, 0, 0, 0, 0
db 0, 0, 0, 0, 0, 0, 0, 0
db 0, 0, 0, 0, 0, 0, 0, 0
mcbfirst: dw 0
seccount: dw 0
Now lets build our disk. If you are running the previous tutorial in VirtualBox Remember to remove the disk or close virtual box before assembling the disk image.
> nasm demoos.asm -o demoos.bin > nasm osdisk.asm -o osdisk.img
Your osdisk.img can now be loaded with VirtualBox. The result should be as follows:
DEMO OS V0.14 A:\> dir Volume in drive A is DEMO OS DSK Volume Serial Number is 2394-C726 DEMOOS BIN A:\>Disk: VOL | Index | Disk: COM Loader