I have this kernel with the shell, and I'm trying to put the time and date commands in it but can't seem to make it work. It shows no error while compiling but it doesn't do anything when I test it. Can anyone tell me what I'm doing wrong here?

Here's the code so far:

;*****************start of the kernel code***************
[org 0x000]
[bits 16]
[SEGMENT .text]

;START #####################################################
    mov ax, 0x0100                      ;location where kernel is loaded
    mov ds, ax
    mov es, ax
    
    cli
    mov ss, ax                          ;stack segment
    mov sp, 0xFFFF                      ;stack pointer at 64k limit
    sti

    push dx
    push es
    xor ax, ax
    mov es, ax
    cli
    mov word [es:0x21*4], _int0x21      ; setup interrupt service
    mov [es:0x21*4+2], cs
    sti
    pop es
    pop dx

    mov si, strWelcomeMsg   		; load message
    mov al, 0x01            		; request sub-service 0x01
    int 0x21

    call _shell                         ; call the shell
    
    int 0x19                ; reboot
;END #######################################################

_int0x21:
    _int0x21_ser0x01:       ;service 0x01
    cmp al, 0x01            ;see if service 0x01 wanted
    jne _int0x21_end        ;goto next check (now it is end)
    
_int0x21_ser0x01_start:
    lodsb                   ; load next character
    or  al, al              ; test for NUL character
    jz  _int0x21_ser0x01_end
    mov ah, 0x0E            ; BIOS teletype
    mov bh, 0x00            ; display page 0
    mov bl, 0x07            ; text attribute
    int 0x10                ; invoke BIOS
    jmp _int0x21_ser0x01_start
    _int0x21_ser0x01_end:
    jmp _int0x21_end

    _int0x21_end:
    iret

_shell:
    _shell_begin:
    					;move to next line
    call _display_endl
    					;display prompt
    call _display_prompt
    					;get user command
    call _get_command
               				;split command into components
    call _split_cmd
        				;check command & perform action
        				; empty command
_cmd_none:              
    mov si, strCmd0
    cmp BYTE [si], 0x00
    jne _cmd_ver                	;next command
    jmp _cmd_done
        
    					; display version
_cmd_ver:               
    mov si, strCmd0
    mov di, cmdVer
    mov cx, 4
    repe cmpsb
    jne _cmd_cls   	        	;next command
        
    call _display_endl
    mov si, strOsName               	;display version
    mov al, 0x01
    int 0x21
    call _display_space
    mov si, txtVersion              	;display version
    mov al, 0x01
    int 0x21
    call _display_space

    mov si, strMajorVer             
    mov al, 0x01
    int 0x21
    mov si, strMinorVer
    mov al, 0x01
    int 0x21
    jmp _cmd_done

_cmd_cls:               
    mov si, strCmd0
    mov di, cmdCls
    mov cx, 4
    repe cmpsb
    jne _cmd_date   	        	;next command
        

    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl
    call _display_endl

    mov bh, 0
    mov dl, 0
    mov dh, 00
    mov ah, 02
    int 10h
    jmp _cmd_done

_cmd_date:               
    mov si, strCmd0
    mov di, cmdDate
    mov cx, 4
    repe cmpsb
    jne _cmd_time   	        	;next command
        

    jmp overdata 

    overdata: 
        mov ah,4    
        int 1Ah    

        mov di,datestring  

        mov al,dh     
        call byte2hex 
        mov al,'-'   
        stosb         
        mov al,dl    
        call byte2hex
        mov al,'-'    
        stosb       
        mov ax,cx    
        call word2hex 
        mov al,'$'    
        stosb        

        mov dx,datestring     ;just like "Hello World!"
        mov ah,9      
        int 21h
        mov ah,4Ch   
        int 21h

    word2hex:
        mov bx,ax        
        shr ax,12         
        call nyb2hex     
        mov ax,bx        
        shr ax,8          
        call nyb2hex    
       mov ax,bx
    byte2hex:
        mov bx,ax   
        shr ax,4
        call nyb2hex
        mov ax,bx
    nyb2hex:
        and al,0Fh    
        cmp al,10     
                  
        ;sbb al,105  
        ;das         
        jc okdigit   
        add al,7     
    okdigit:
        add al,30h   
        ;int 029h     
        stosb         
        ret          

    jmp _cmd_done

_cmd_time: 
    mov si, strCmd0
    mov di, cmdTime
    mov cx, 4
    repe cmpsb
    jne _cmd_hlp

    jmp _WasteTime

    global _WasteTime
     
    _WasteTime:
        mov  bx, sp
        mov  bx, [ss:bx+02h]

        push si
        push di

        mov  ah, 00h
        int  1Ah
        
        mov  di, cx
        mov  si, dx

    .Waster:        
        mov  ah, 00h
        int  1Ah

        sub  dx, si
        sbb  cx, di

        cmp  cx, 0
        jne  .EndOfProc

        cmp  dx, bx
        jb   .Waster

    .EndOfProc:
        pop  di
        pop  si
        ret


    jmp _cmd_done

_cmd_hlp:
    mov si, strCmd0
    mov di, cmdHlp
    mov cx, 4
    repe cmpsb
    jne _cmd_abt   	        	;next command

    call _display_endl
    mov si, strHelp               	;display help
    mov al, 0x01
    int 0x21
    call _display_space
    mov si, txtHelp              	;display help
    mov al, 0x01
    int 0x21

    mov si, strCmdOne               	;display command
    mov al, 0x01
    int 0x21
    mov si, strCmdTwo             
    mov al, 0x01
    int 0x21
    mov si, strCmdThree
    mov al, 0x01
    int 0x21
    mov si, strCmdFour
    mov al, 0x01
    int 0x21
    mov si, strCmdFive             
    mov al, 0x01
    int 0x21
    mov si, strCmdSix
    mov al, 0x01
    int 0x21
    jmp _cmd_done


_cmd_abt:               
    mov si, strCmd0
    mov di, cmdAbt
    mov cx, 4
    repe cmpsb
    jne _cmd_exit   	        	;next command
        
    call _display_endl
    mov si, txtAbout               	;display about
    mov al, 0x01
    int 0x21
    call _display_space
    mov si, strAbout              	;display about
    mov al, 0x01
    int 0x21
    call _display_space

    mov si, strMajorAbt             
    mov al, 0x01
    int 0x21
    mov si, strMinorAbt
    mov al, 0x01
    int 0x21
    jmp _cmd_done

        				; exit shell
_cmd_exit:              
    mov si, strCmd0
    mov di, cmdExit
    mov cx, 5
    repe cmpsb
    jne _cmd_unknown            	;next command

    je _shell_end                   	;exit from shell


_cmd_unknown:
    call _display_endl
    mov si, msgUnknownCmd           	;unknown command
    mov al, 0x01
    int 0x21

_cmd_done:
    					;call _display_endl
    jmp _shell_begin
        
_shell_end:
    ret

_get_command:
        				;initiate count
    mov BYTE [cmdChrCnt], 0x00
    mov di, strUserCmd

_get_cmd_start:
    mov ah, 0x10            		;get character
    int 0x16

    cmp al, 0x00            		;check if extended key
    je _extended_key
    cmp al, 0xE0            		;check if new extended key
    je _extended_key

    cmp al, 0x08            		;check if backspace pressed
    je _backspace_key

    cmp al, 0x0D            		;check if Enter pressed
    je _enter_key

    mov bh, [cmdMaxLen]             	;check if maxlen reached
    mov bl, [cmdChrCnt]
    cmp bh, bl
    je _get_cmd_start
        				;add char to buffer, display it and start again
    mov [di], al                    	;add char to buffer
    inc di                              ;increment buffer pointer
    inc BYTE [cmdChrCnt]    		;inc count

    mov ah, 0x0E                    	;display character
    mov bl, 0x07
    int 0x10
    jmp _get_cmd_start

_extended_key:                  	;extended key - do nothing now
    jmp _get_cmd_start

_backspace_key:
    mov bh, 0x00                    	;check if count = 0
    mov bl, [cmdChrCnt]
    cmp bh, bl
    je _get_cmd_start          		;yes, do nothing
        
    dec BYTE [cmdChrCnt]    		;dec count
    dec di
        				;check if beginning of line
    mov ah, 0x03                	;read cursor position
    mov bh, 0x00
    int 0x10

    cmp dl, 0x00
    jne _move_back
    dec dh
    mov dl, 79
    mov ah, 0x02
    int 0x10

    mov ah, 0x09            		; display without moving cursor
    mov al, ' '
    mov bh, 0x00
    mov bl, 0x07
    mov cx, 1                       	; times to display
    int 0x10
    jmp _get_cmd_start

_move_back:
    mov ah, 0x0E            		; BIOS teletype acts on backspace!
    mov bh, 0x00
    mov bl, 0x07
    int 0x10
    mov ah, 0x09           		; display without moving cursor
    mov al, ' '
    mov bh, 0x00
    mov bl, 0x07
    mov cx, 1                       	; times to display
    int 0x10
    jmp _get_cmd_start

_enter_key:
    mov BYTE [di], 0x00
    ret

_split_cmd:
        				;adjust si/di
    mov si, strUserCmd
        				;mov di, strCmd0
        				;move blanks
_split_mb0_start:
    cmp BYTE [si], 0x20
    je _split_mb0_nb
    jmp _split_mb0_end

_split_mb0_nb:
    inc si
    jmp _split_mb0_start

_split_mb0_end:
    mov di, strCmd0

_split_1_start:                 	;get first string
    cmp BYTE [si], 0x20
    je _split_1_end
    cmp BYTE [si], 0x00
    je _split_1_end
    mov al, [si]
    mov [di], al
    inc si
    inc di
    jmp _split_1_start

_split_1_end:
    mov BYTE [di], 0x00
        				;move blanks
_split_mb1_start:
    cmp BYTE [si], 0x20
    je _split_mb1_nb
    jmp _split_mb1_end

_split_mb1_nb:
    inc si
    jmp _split_mb1_start

_split_mb1_end:
    mov di, strCmd1

_split_2_start:                 	;get second string
    cmp BYTE [si], 0x20
    je _split_2_end
    cmp BYTE [si], 0x00
    je _split_2_end
    mov al, [si]
    mov [di], al
    inc si
    inc di
    jmp _split_2_start

_split_2_end:
    mov BYTE [di], 0x00
			        	;move blanks
_split_mb2_start:
    cmp BYTE [si], 0x20
    je _split_mb2_nb
    jmp _split_mb2_end

_split_mb2_nb:
    inc si
    jmp _split_mb2_start

_split_mb2_end:
    mov di, strCmd2

_split_3_start:                 	;get third string
    cmp BYTE [si], 0x20
    je _split_3_end
    cmp BYTE [si], 0x00
    je _split_3_end
    mov al, [si]
    mov [di], al
    inc si
    inc di
    jmp _split_3_start

_split_3_end:
    mov BYTE [di], 0x00
        				;move blanks
_split_mb3_start:
    cmp BYTE [si], 0x20
    je _split_mb3_nb
    jmp _split_mb3_end

_split_mb3_nb:
    inc si
    jmp _split_mb3_start

_split_mb3_end:
    mov di, strCmd3


_split_4_start:                 	;get fourth string
    cmp BYTE [si], 0x20
    je _split_4_end
    cmp BYTE [si], 0x00
    je _split_4_end
    mov al, [si]
    mov [di], al
    inc si
    inc di
    jmp _split_4_start

_split_4_end:
    mov BYTE [di], 0x00
        				;move blanks
_split_mb4_start:
    cmp BYTE [si], 0x20
    je _split_mb4_nb
    jmp _split_mb4_end

_split_mb4_nb:
    inc si
    jmp _split_mb4_start

_split_mb4_end:
    mov di, strCmd4


_split_5_start:                 	;get last string
    cmp BYTE [si], 0x20
    je _split_5_end
    cmp BYTE [si], 0x00
    je _split_5_end
    mov al, [si]
    mov [di], al
    inc si
    inc di
    jmp _split_5_start

_split_5_end:
    mov BYTE [di], 0x00
    ret

_display_space:
    mov ah, 0x0E                        ; BIOS teletype
    mov al, 0x20
    mov bh, 0x00                        ; display page 0
    mov bl, 0x07                        ; text attribute
    int 0x10                            ; invoke BIOS
    ret

_display_endl:
    mov ah, 0x0E            		; BIOS teletype acts on newline!
    mov al, 0x0D
    mov bh, 0x00
    mov bl, 0x07
    int 0x10
    mov ah, 0x0E            		; BIOS teletype acts on linefeed!
    mov al, 0x0A
    mov bh, 0x00
    mov bl, 0x07
    int 0x10
    ret

_display_prompt:
    mov si, strPrompt
    mov al, 0x01
    int 0x21
    ret



[SEGMENT .data]
    strWelcomeMsg db  "Welcome to GeoLiz NaviOS", 0x00
    strPrompt     db  "==>", 0x00
    cmdMaxLen     db  255                     ;maximum length of commands

    strOsName     db  "GeoLiz", 0x00    ;OS details
    strMajorVer   db  "0", 0x00
    strMinorVer   db  ".7", 0x0D, 0x0A, 0x00

    strHelp       db  "List of ", 0x00    ;Help
    strCmdOne     db  "ver-Get version ", 0x0D, 0x0A, 0x00
    strCmdTwo     db  "exit-Reboot ", 0x0D, 0x0A, 0x00
    strCmdThree   db  "date-Get date today ", 0x0D, 0x0A, 0x00
    strCmdFour    db  "time-Get time now ", 0x0D, 0x0A, 0x00
    strCmdFive    db  "help-list commands ", 0x0D, 0x0A, 0x00
    strCmdSix     db  "abt-about creator", 0x0D, 0x0A, 0x00

    strAbout      db  "GeoLiz NaviOS", 0x0D, 0x0A, 0x00  ;about OS
    strMajorAbt   db  "Creators: Geo and Liz", 0x0D, 0x0A, 0x00
    strMinorAbt   db  " Created: Sept.20,2007", 0x0D, 0x0A, 0x00

    cmdVer        db  "ver", 0x00             ; internal commands
    cmdExit       db  "exit", 0x00
    cmdDate       db  "date", 0x00
    cmdTime       db  "time", 0x00
    cmdHlp        db  "help", 0x00
    cmdAbt        db  "abt", 0x00
    cmdCls        db  "cls", 0x00


    datestring times 0Eh db 0 

    txtVersion    db  "Version", 0x00 	;messages and other strings
    txtHelp       db  "Commands:", 0x0D, 0x0A, 0x00
    txtAbout      db  "About", 0x0D, 0x0A, 0x00
    msgUnknownCmd db  "Unknown command!", 0x00


[SEGMENT .bss]
    strUserCmd    resb    256             ;buffer for user commands
    cmdChrCnt     resb    1               ;count of characters
    strCmd0       resb    256             ;buffers for the command components
    strCmd1       resb    256
    strCmd2       resb    256
    strCmd3       resb    256
    strCmd4       resb    256

;********************end of the kernel code********************

You have several "int 0x21" calls in your code. These are DOS calls:

http://www.ctyme.com/intr/int-21.htm

Since DOS is not loaded (indeed, you are writing your own OS), then you cannot use these functions. You must restrict yourself to just the BIOS calls.

Nathan.