Power-Programmierung/CD1.mdf/assemblr/library/sampler0/resident.asm

Assembly Source File | 1987-08-30 | 10.9 KB | 399 lines

; This code illustrates how to install and deinstall a TSR and under what
; circumstances the body of a TSR should be given control.
;
; The hot keys in this example are the Alt + Left Shift keys.  This hot key
; combination is defined in the variable hot_keys and can be changed to suit
; the user by changing the bit pattern.
;
; This example is intended to illustrate the recommendations made in the
; following articles:
;
;    "DOS: Terminate and Stay Resident", M. Steven Baker
;    Programmer's Journal, Nov/Dec 1986, pages 26 - 30
;
;    "Coding Guidelines for Resident Programs", Graham Pearson
;    Programmer's Journal, Mar/Apr 1987, pages 34 - 38
;
;
; The author can be reached at the following address:
;    Kudos Software,  9111 Cadawac Road,  Houston, Texas 77074
;    Tel: [phone]

;******************************************************************************

DELAY_COUNT    EQU    36        ;Timer counts between hot key triggers
                    ;36 ticks = approx. 2 seconds

; Locations of BIOS Data needed by the resident program

bios_data    segment at 40H
    org        17H        ;Keyboard status flags
    kbd_status    dw    ?
    org        6CH        ;Timer count - low word. This rolls
    low_timer    dw    ?    ;around 0FFFFH once per hour
bios_data    ends

;------------------------------------------------------------------------------

code        segment
    assume    cs:code, ds:nothing, es:nothing, ss:nothing
    org    100H            ;Define starting point for .COM file

entry_point:
    jmp    install         ;Skip over the code to be made resident

;------------------------------------------------------------------------------

    hot_keys    dw    01010B    ;Hot key bits -> Alt + Left Shift

    this_time    dw    ?    ;Most-recent time hot keys detected
    trig_time    dw    ?    ;Last time resident code was triggered

    dos_busy    label    dword    ;Pointer to "DOS is busy" flag
    dos_busy_off    dw    ?    ;These values are initialized during
    dos_busy_seg    dw    ?    ;the "install" process

    criterr_flag    dw    ?    ;Used by diverted INT 24H

;------------------------------------------------------------------------------

; Replacement for INT 24H - critical DOS error

diverted_int24:

    mov    cs:criterr_flag,0FFFFH    ;Switch error flag ON
    xor    al,al            ;Tell DOS to ignore the error
    iret                ;Return to DOS

    int_24_vect    label    dword
    int_24_off    dw    ?    ;These values are initialized each time
    int_24_seg    dw    ?    ;the TSR body takes control

;------------------------------------------------------------------------------

; Replacement for INT 9 - keyboard hardware interrupt

diverted_int9:

    pushf                ;Simulate an INT 9 to pass through the
    call_int9    db    09AH    ;original BIOS interrupt handler
    int_9_vect    label    dword
    int_9_off    dw    ?    ;These values are initialized during
    int_9_seg    dw    ?    ;the "install" process

    push    ds            ;Save all registers used by this
    push    bx            ;section of code
    lds    bx,dos_busy        ;See if DOS is busy
    cmp    byte ptr [bx],0
    pop    bx            ;Restore all registers
    pop    ds
    jz    get_bios_data        ;Zero means DOS is not busy

dos_is_busy:
    iret                ;Return control to interrupted process

;------------------------------------------------------------------------------

; Replacement for INT 28 - generated by DOS, esp. during keyboard I/O functions

diverted_int28:

    pushf                ;Simulate an INT 28H to pass through
    call_int28    db    09AH    ;the original DOS interrupt handler
    int_28_vect    label    dword
    int_28_off    dw    ?    ;These values are initialized during
    int_28_seg    dw    ?    ;the "install" process

;------------------------------------------------------------------------------

get_bios_data:

    sti                ;Restore interrupts
    push    ds            ;Save all registers used by this
    push    bx            ;section of code

    mov    bx,bios_data        ;Retrieve BIOS Data values
    mov    ds,bx
    assume    ds:bios_data

    mov    bx,low_timer        ;Retrieve and save timer count
    mov    cs:this_time,bx
    mov    bx,kbd_status        ;Retrieve keyboard status bits

    push    cs            ;Point DS to our code segment
    pop    ds
    assume    ds:code

chk_keys:
    and    bx,hot_keys        ;See if hot keys are pressed
    cmp    bx,hot_keys
    jne    back_to_applic

chk_timer:
    mov    bx,this_time
    cmp    bx,trig_time        ;Enter resident routine if timer
    jb    time_is_right        ;count has rolled around the hour

    sub    bx,trig_time
    sub    bx,DELAY_COUNT        ;Transfer to resident code only if
    jnc    time_is_right        ;elapsed time between hot keys is
                    ;greater than delay count
back_to_applic:
    pop    bx            ;Restore all registers
    pop    ds
    iret                ;Return control to interrupted process

;------------------------------------------------------------------------------

time_is_right:
    mov    bx,this_time        ;Update latest trigger time
    mov    trig_time,bx
    pop    bx            ;Restore all registers
    pop    ds

;******************************************************************************

; This is the start of the application-dependent resident code

start_program:

    push    ax            ;Save all registers used by the
    push    bx            ;resident application
    push    cx
    push    dx
    push    si
    push    di
    push    bp
    push    ds
    push    es

    push    cs            ;Point DS to our CS
    pop    ds

    mov    ax,3524H        ;Get current INT 24H vector
    int    21H
    mov    int_24_off,bx
    mov    int_24_seg,es
    mov    ax,2524H        ;Redirect INT 24H
    mov    dx,offset diverted_int24
    int    21H


;******************************************************************************

    ; Include application specific code here

;******************************************************************************


restore_int24:
    lds    dx,int_24_vect        ;Restore INT 24H
    mov    ax,2524H        ;Error in PJ listing (was 2509H)
    int    21H

    pop    es            ;Restore all registers
    pop    ds
    pop    bp
    pop    di
    pop    si
    pop    dx
    pop    cx
    pop    bx
    pop    ax
    iret                ;Return control to interrupted process

; This is the end of the application-dependent resident code

    end_of_res    label    word

;******************************************************************************

; This procedure installs the resident section of code in memory.
; It performs the following tasks:
;
;    1    Make sure the operating system is at least DOS 2.00
;
;    2    Make sure the resident code is not already installed in memory
;    If it IS already installed, remove it from memory
;
;    3    Retrieve an available vector for installing the signature
;
;    4    Retrieve vector to "DOS is busy" and save it for use by resident code
;
;    5    Update the interrupt vectors required by resident code.
;
;    6    Install the signature in the available vector found in step 3
;
;    7    Terminate and stay resident - transfer control back to DOS

;------------------------------------------------------------------------------

install:

; Make sure that the operating system is at least DOS 2.00

    mov    ah,30H
    int    21H
    or    al,al
    jnz    chk_vectors

    mov    dx,offset baddos_msg    ;DS:DX -> Display "bad DOS" message
    mov    ah,9
    int    21H

    int    20H            ;Return to DOS the old-fashioned way

;------------------------------------------------------------------------------

; See if the resident code is already installed in memory.
; If so, remove the resident code from memory.
; If not, retain an available interrupt vector for later use as a signature.

chk_vectors:
    push    ds            ;Save DS -> CS

    xor    ax,ax            ;Search 32 interrupt vectors starting
    mov    ds,ax            ;at INT 60H - user interrupt area
    mov    si,60H * 4
    mov    cx,20H

next_vector:
    mov    ax,[si + 2]
    or    ax,ax            ;If segment value is zero, get offset
    jz    get_vect_off        ;value

    cmp    ax,0D0C7H        ;Check interrupt segment value against
    jne    vector_loop        ;resident code signature

deinstall:
    mov    bx,[si]         ;Retrieve original resident code
                    ;segment value
    xor    ax,ax
    mov    [si],ax         ;Remove signature from the
    mov    [si + 2],ax        ;interrupt vector

restore_int9:
    mov    ds,bx            ;DS -> original resident code segment
    lds    dx,int_9_vect        ;Restore INT 9 - keyboard I/O
    mov    ax,2509H
    int    21H

restore_int28:
    mov    ds,bx            ;DS -> original resident code segment
    lds    dx,int_28_vect        ;Restore INT 28 - DOS interrupt
    mov    ax,2528H
    int    21H

    mov    es,bx            ;ES -> code segment to be deinstalled
    mov    ah,49H
    int    21H            ;Free allocated memory

    mov    es,es:[2CH]        ;ES -> environment to be deinstalled
    mov    ah,49H
    int    21H            ;Free allocated memory

    pop    ds            ;Restore DS -> CS
    mov    dx,offset remove_msg    ;DS:DX -> Display "remove" message
    mov    ah,9
    int    21H

    mov    ax,4C01H        ;Return error code of 1
    int    21H            ;Return to DOS with error code

get_vect_off:
    cmp    word ptr [si],0     ;If offset value is zero, this vector
    je    found_vector        ;is available for our use

vector_loop:
    add    si,4            ;Interrogate next vector
    loop    next_vector

found_vector:

    ;Make sure we successfully complete the install process before
    ;installing the signature in this available interrupt vector

    pop    ds            ;Restore Data Segment
    mov    free_vector,si        ;Save free vector for later

;------------------------------------------------------------------------------

; Retrieve original interrupt vectors and install these in the resident code.
; Redirect the interrupt vectors to point to resident code.
; Install signature in available interrupt vector.

    push    es            ;Save ES -> CS

    mov    ah,34H            ;Retrieve segment + offset
    int    21H            ;pointer to "DOS is busy" flag
    mov    dos_busy_off,bx
    mov    dos_busy_seg,es

    mov    ax,3509H        ;Get current INT 9H vector
    int    21H
    mov    int_9_off,bx
    mov    int_9_seg,es
    mov    ax,2509H        ;Redirect INT 9H
    mov    dx,offset diverted_int9
    int    21H

    mov    ax,3528H        ;Get current INT 28H vector
    int    21H
    mov    int_28_off,bx
    mov    int_28_seg,es
    mov    ax,2528H        ;Redirect INT 28H
    mov    dx,offset diverted_int28
    int    21H

    pop    es            ;Restore ES -> CS
    mov    di,free_vector        ;Retrieve value found earlier

    push    ds            ;Save DS -> CS
    xor    ax,ax            ;DS -> interrupt vectors
    mov    ds,ax
    mov    [di],cs         ;Install signature in the available
    mov    word ptr [di+2],0D0C7H    ;interrupt vector
    pop    ds            ;Restore DS -> CS

;------------------------------------------------------------------------------

; Display installed message

    mov    dx,offset success_msg    ;DS:DX -> Display "success" message
    mov    ah,9
    int    21H

;------------------------------------------------------------------------------

; Prepare for program "terminate and stay resident"

    mov    dx,offset end_of_res    ;Calculate the amount of memory used
    dec    dx            ;by the resident code
    or    dx,0FH
    inc    dx            ;Round up to the nearest paragraph

    mov    cl,4            ;Convert code size to paragraphs
    shr    dx,cl
    mov    ax,03100H        ;Return error code of 0
    int    21H            ;Terminate but stay resident

;------------------------------------------------------------------------------

    free_vector    dw    ?    ;Pointer to available interrupt vector

    copyright    db    '  Copyright (c) 1986 Kudos Software  '

    baddos_msg    db    'TSR will not run with DOS 1.XX'
            db    0DH, 0AH, '$'

    remove_msg    db    'TSR is no longer resident in memory'
            db    0DH, 0AH,'$'

    success_msg    db    'TSR successfully installed in memory'
            db    0DH, 0AH, '$'

;------------------------------------------------------------------------------

code        ends
        end    entry_point    ;Define entry point for .COM file