Programmer Power Tools/Programmer Power Tools.iso/microcrn/issue_32.arc/DISK.FIG

Text File | 1979-12-31 | 4.8 KB | 196 lines

((Disk Figs 1,2, and A printouts go with this article))

((Disk Figure 1 - Program PC-DU))

; PC-DU, a program to read and write disk sectors
; Illustrates disk I/O using ROM-BIOS interrupt 13h
;
;
STACK    SEGMENT    PARA STACK 'STACK'
    DB    256 DUP (0) ; 256 bytes for the stack
STACK    ENDS
;
;
DATA    SEGMENT    PARA PUBLIC 'DATA'
BUFFER    DB    2048 DUP (0); Enough buffer space for 4 sectors
ERRMSG    DB    'Something isn't working ! '
SUCCES  DB    'Something is    working ! '
DATA    ENDS
;
;
CODE    SEGMENT    PARA PUBLIC 'CODE'
START    PROC    FAR
;
;
; Program prologue
;
    ASSUME    CS:CODE
    PUSH    DS    ; Save PSP Seg Addr
    MOV    AX,0
    PUSH    AX    ; Save Ret Addr offset (PSP + 0)
    MOV    AX,DATA
    MOV    DS,AX    ; Setup Data Seg
    ASSUME    DS:DATA
    MOV    ES,AX    ; Setup Extra Seg
    ASSUME    ES:DATA
;
;
; Read sectors from disk into memory
; In this example we'll read the 4 directory tracks --
; Side 0, Track 0, Sectors 4,5,6,7
;
;
    MOV    CX,3    ; Retry 3 times if necessary
RETRY:    PUSH    CX    ; Save retry count
    MOV    BX,OFFSET BUFFER; We'll read the sectors into
            ; a buffer
    MOV    DL,0    ; DL gets the drive (0=A;1=B)
    MOV    DH,0    ; DH gets the side(0 or 1)
    MOV    CH,0    ; CH gets the track(0-39)
    MOV    CL,4    ; CL gets the sector(1-8)
    MOV    AL,4    ; No. of sectors to read
    MOV    AH,2    ; Service call 2 = read
    INT    13h    ; BIOS disk I/O routine
    POP    CX    ; Restore retry count
    JNC    WRITSEC    ; Branch to write, if read ok
    MOV    AH,0    ; Otherwise, reset
    INT    13h
    LOOP    RETRY    ; Try again (up to 3 times)
ERROR:    MOV    BX,OFFSET ERRMSG
    CALL    DISPLAY ; Display the error message
    RET        ; Return control to DOS
;
;
; Write sectors back out to disk
;
WRITSEC:MOV    BX,OFFSET BUFFER; Here's the buffer where the
            ; read sectors are
    MOV    DL,0    ; DL gets the drive (0=A;1=B)
            ; Change this to 1 for a copy (see text)
    MOV    DH,0    ; DH gets the side(0 or 1)
    MOV    CH,0    ; CH gets the track(0-39)
    MOV    CL,4    ; CL gets the sector(1-8)
    MOV    AL,4    ; No. of sectors to write
    MOV    AH,3    ; Service call 3 = write
    INT    13h    ; BIOS disk I/O routine
    JNC    SUCCESS ; Branch to ok message, if ok
    JNC    ERROR    ; Else branch to error message
;
; Go get the message we want and display it
;
SUCCESS:MOV    BX,OFFSET SUCCES; Here's where the good message
            ; is
    CALL    DISPLAY    ; Display the good message
    RET        ; Return control to DOS
;
; Subroutine (or procedure) to set up display
;
DISPLAY    PROC    NEAR
    MOV    CX,26    ; Display 26 characters
DISP:    MOV    AL,[BX] ; Get next char to display
    CALL    DISPCHAR; Display char
    INC    BX    ; Point to next char
    LOOP    DISP    ; Loop 26 times (value of CX reg)
    MOV    AL,0DH    ; carriage return
    CALL    DISPCHAR;
    MOV    AL,0AH    ; line feed
    CALL    DISPCHAR
    RET        ; Return control to caller of DISPLAY
DISPLAY    ENDP
;
; Subroutine to actually display messages
;
DISPCHAR PROC    NEAR
    PUSH    BX      ; Save BX
    MOV    BX,0    ; Select display page 0
    MOV    AH,14    ; Function code for write
    INT    10H    ; Video interrupt
    POP    BX    ; Restore BX
    RET        ; Return control to caller of DISPCHAR
DISPCHAR ENDP
;
;
START    ENDP
CODE    ENDS
    END    START



((Disk Figure 2 - Turbo Pascal & external assembler shell))

program PC_DU;       {  Turbo Pascal & assembler shell:
                         for interactive PC-DU;
                         does not include retries for reads
                         or interactive details  }

TYPE
    Size_of_Sector = ARRAY[0..511] of BYTE; { set up buffer
                                               to hold 1 sector }

VAR
    Buffer : Size_of_Sector;
        Drive, Track, Side, Sector : integer;

function SECREAD(
    VAR    B : Size_of_Sector;
        Drive : integer;
        Track : integer;
        Side : integer;
        Sector : integer)
    : BYTE;

    external 'secread.com';  { Secread is an external assembly
                                  language subroutine  }

function SECWRIT(
    VAR    B : Size_of_Sector;
        Drive : integer;
        Track : integer;
        Side : integer;
        Sector : integer)
    : BYTE;

    external 'secwrit.com';  { Secwrite is an external assembly
                  language subroutine }

BEGIN
  IF SECREAD(Buffer,Drive,Track,Side,Sector)= 0 {If no error}
     THEN
        IF SECWRIT(Buffer,Drive,Track,Side,Sector)=0 {If no error}
            THEN  Writeln('success is ours!')
           ELSE write('Unable to read Track', Track,
                            'Side',Side, 'Sector',Sector);
END.

SECWRIT.ASM             ;subroutine to write 1 disk sector

code    segment    'code'
    assume    cs:code
;
SECWRIT    proc    near
    push    BP
    MOV    BP,SP
    PUSH    DS
    POP    ES
    MOV    BX,[BP+12]
    MOV    BL,[BP+10]
    MOV    CH,[BP+8]
    MOV    DH,[BP+6]
    MOV    CL,[BP+4]
    MOV    AL,1
    MOV    AH,3
    INT    19
    MOV    AL,AH
    POP    BP
    RET    10
SECREAD ENDP
code    ends
    end


((this is Disk Fig. A))

MOV    AH,0
INT    13H