Cream of the Crop 1/Cream of the Crop 1.iso/PROGRAM/CPPTASK.ARJ/TSKDOS.ASM

Assembly Source File | 1991-07-26 | 20KB | 973 lines

;
;    CTask - DOS access module.
;
;    Public Domain Software written by
;        Thomas Wagner
;        Patschkauer Weg 31
;        D-1000 Berlin 33
;        West Germany
;
;
; The DOS interrupt (and the related direct disk I/O interrupts) are
; not reentrant. Access to DOS thus has to be channelled such that no
; two tasks use DOS services simultaneously. However, there is one
; exception to this rule. Whenever DOS is waiting for the keyboard, it
; issues a special interrupt, INT 28h, to signal that background
; processing for functions > 0Ch may be performed. This is used in the
; DOS interface for CTask in the following manner:
;
;   A task issuing a DOS interrupt will request one of two resources:
;   "lower_dos" for functions <= 0C, "upper_dos" for functions > 0C.
;   If a task gets access to "lower_dos", it will also request the
;   "upper_dos" resource to lock out other tasks from interrupting.
;   This "upper_dos" resource is shortly released on each INT 28, and
;   then immediately reclaimed, with task priority temporarily raised
;   to the maximum value. The first task waiting to execute a
;   function > 0C will thus be scheduled to execute the request, but
;   the resource will be reassigned to the INT 28 handler as soon as
;   this request terminates, so the waiting task will not be delayed too
;   long.
;
; There are two additional safety measures which have to be taken to
; avoid getting into conflicts with other resident background programs,
; especially the DOS PRINT background spooler:
;
;   Before requesting any resource, the status of the DOS critical section
;   flag is checked. If this flag is set, the task is made waiting for
;   the flag to be cleared.
;   Only the task that set the flag will be allowed access to DOS.
;
;   Before actually executing the request, the status of the DOS in-use
;   flag is checked. If this flag is set, the task enters a busy waiting
;   loop, calling the scheduler so that the processor is not tied up.
;
; NOTE: The method for checking the status of DOS is described in-depth
;    in the book "The MS-DOS Encyclopedia" from Microsoft Press, in
;    the chapter on TSR programming. The logic in this module was
;    developed without the help of this book, so if you compare
;    the code here with the routines in the Encyclopedia, you may
;    notice that not all re-entry conditions are checked here.
;    According to my experience with debugging TSR's and CTask, the
;    logic should be sufficient for all but the most obscure TSR's.
;    If you want to be completely on the safe side, you might consider
;    adding the more thorough checks listed in the Encyclopedia.
;
;
    name    tskdos
;
    .model    large
;
    public    _tsk_install_dos
    public    _tsk_remove_dos
;
;
    include    tsk.mac
;
CSECT        =    2ah    ; Critical Section Interrupt
get_in_use_flag    =    34h    ; DOS-function to get in_use_flag address
;
;
intseg    segment at 0
        org    20h*4
termoff        dw    ?    ; program terminate vector
termseg        dw    ?
        org    21h*4
idosoff        dw    ?    ; dos interrupt
idosseg        dw    ?
        org    25h*4
absreadoff    dw    ?    ; absolute disk read
absreadseg    dw    ?
        org    26h*4
abswriteoff    dw    ?    ; absolute disk write
abswriteseg    dw    ?
        org    27h*4
keepoff        dw    ?    ; Terminate but stay resident
keepseg        dw    ?
        org    28h*4
idleoff        dw    ?    ; dos idle interrupt
idleseg        dw    ?
        org    CSECT*4
csectoff    dw    ?    ; dos critical section
csectseg    dw    ?
;
intseg    ends
;
;----------------------------------------------------------------------------
;
;       externally defined variables
;
        extrn   _tsk_current: dword
        extrn   _lower_dos: resource
        extrn   _upper_dos: resource
        extrn   _critical: flag
;
;       externally defined functions
;
        extrn   _asm_request_resource: far
        extrn   _asm_release_resource: far
        extrn   _asm_set_flag: far
        extrn   _asm_clear_flag: far
        extrn   _asm_wait_flag_clear: far
        extrn   _asm_remove_tasker: far
        extrn   scheduler: far
;
    .data
;
;
term_err_msg    db    0dh,0ah,"Program terminated - CTask uninstalled"
        db    0dh,0ah,'$'
;
idle_active    db    0            ; Idle-Interrupt active
dos310        db    0        ; DOS version >= 3.10
;
;
    .data?
;
in_use        dd    ?        ; Adress of DOS in-use-flag
in_error    dd    ?        ; Adress of DOS error-mode-flag
;
;
idle_ss        dw    ?        ; Stack save
idle_sp        dw    ?
;
        dw    256 dup(?)    ; Stack for IDLE-Interrupt
local_stack    label    word
;
    .code
;
;    Original Interrupt-Entries
;
savtermoff    dw    ?        ; Terminate vector save
savtermseg    dw    ?
;
savdos        label    dword        ; original DOS-Entry
savdosoff    dw    ?
savdosseg    dw    ?
;
savidle        label    dword        ; original IDLE-Entry
savidleoff    dw    ?
savidleseg    dw    ?
;
savcsect    label    dword        ; Critical Section save
savcsectoff    dw    ?
savcsectseg    dw    ?
;
savabsread    label    dword        ; Absolute Disk Read save
savabsreadoff    dw    ?
savabsreadseg    dw    ?
;
savabswrite    label    dword        ; Absolute Disk Write save
savabswriteoff    dw    ?
savabswriteseg    dw    ?
;
savkeepoff    dw    ?        ; Terminate resident vector save
savkeepseg    dw    ?
;
critsect_active    db    0        ; DOS Critical Section active
ctask_active    db    0        ; CTask DOS call active
crit_task    dd    ?        ; Task requesting critical section
;
;
dos    macro
    pushf
    cli
    call    cs:savdos
    endm
;
;---------------------------------------------------------------------------
;
    .code
;
;
;    void tsk_install_dos (void)
;
;        Install DOS handler
;
;       Invoked by tasker_class::tasker_class
;
_tsk_install_dos    proc
;
;
;    Get the address of DOS's in_use-flag. This flag indicates that
;    DOS is already active. This might happen if there are other
;    background tasks, like popups or print spoolers, active in
;    parallel to CTask.
;    This is also the address of the critical error flag in DOS. Beginning
;    with DOS 3.10 the flag is located one byte before the in_use_flag.
;    With older DOS versions, we would have to search through DOS for the
;    address. This is omitted here, but you could include the code
;    for pre 3.1 versions from pages 378-379 of the MS-DOS Encyclopedia.
;
    mov    ah,get_in_use_flag
    int    21h
    mov    word ptr in_use,bx
    mov    word ptr in_use+2,es
    mov    word ptr in_error+2,es
;
    push    bx
    mov    ah,30h
    int    21h
    pop    bx
    cmp    al,3
    jb    not_dos3
    cmp    al,0ah
    je    not_dos3    ; OS/2 compatibility box
    cmp    ah,10
    jb    not_dos3
    inc    dos310
    dec    bx
    mov    word ptr in_error,bx
    jmp    short save_ints
;
not_dos3:

;
;    Save old interrupt vectors
;
save_ints:
        push    es
    xor    ax,ax
    mov    es,ax
;
        assume  es:intseg
;
    mov    ax,termoff        ; DOS
    mov    savtermoff,ax
    mov    ax,termseg
    mov    savtermseg,ax
;
    mov    ax,idosoff        ; DOS
    mov    savdosoff,ax
    mov    ax,idosseg
    mov    savdosseg,ax
;
    mov    ax,idleoff        ; IDLE
    mov    savidleoff,ax
    mov    ax,idleseg
    mov    savidleseg,ax
;
    mov    ax,csectoff        ; Critical Section
    mov    savcsectoff,ax
    mov    ax,csectseg
    mov    savcsectseg,ax
;
    mov    ax,absreadoff        ; Absolute Disk read
    mov    savabsreadoff,ax
    mov    ax,absreadseg
    mov    savabsreadseg,ax
;
    mov    ax,abswriteoff        ; Absolute Disk write
    mov    savabswriteoff,ax
    mov    ax,abswriteseg
    mov    savabswriteseg,ax
;
    mov    ax,keepoff        ; Terminate Resident
    mov    savkeepoff,ax
    mov    ax,keepseg
    mov    savkeepseg,ax
;
;    Enter new Interrupt-Entries
;
    cli
    mov    idosoff,offset dosentry        ; DOS-Entry
    mov    idosseg,cs
    mov    idleoff,offset idleentry    ; Idle-Entry
    mov    idleseg,cs
    mov    termoff,offset terminate_int    ; Terminate Process Entry
    mov    termseg,cs
    mov    csectoff,offset critsectint    ; Critical Section Entry
    mov    csectseg,cs
    mov    keepoff,offset keep_int        ; Keep Process Entry
    mov    keepseg,cs
    mov    absreadoff,offset absread_int    ; Absolute Disk Read Entry
    mov    absreadseg,cs
    mov    abswriteoff,offset abswrite_int    ; Absolute Disk Write Entry
    mov    abswriteseg,cs
    sti
        pop     es
;
    ret
;
    assume    es:nothing
;
_tsk_install_dos    endp
;
;
;    void tsk_remove_dos (void)
;
;       Un-install DOS handler
;
_tsk_remove_dos    proc
;
;    Delete resources & flags
;
        push    es
    xor    ax,ax
    mov    es,ax
;
        assume  es:intseg
;
;    Restore interrupt entries
;
    cli
    mov    ax,savtermoff
    mov    termoff,ax
    mov    ax,savtermseg
    mov    termseg,ax
;
    mov    ax,savdosoff
    mov    idosoff,ax
    mov    ax,savdosseg
    mov    idosseg,ax
;
    mov    ax,savidleoff
    mov    idleoff,ax
    mov    ax,savidleseg
    mov    idleseg,ax
;
    mov    ax,savcsectoff
    mov    csectoff,ax
    mov    ax,savcsectseg
    mov    csectseg,ax
;
    mov    ax,savabsreadoff
    mov    absreadoff,ax
    mov    ax,savabsreadseg
    mov    absreadseg,ax
;
    mov    ax,savabswriteoff
    mov    abswriteoff,ax
    mov    ax,savabswriteseg
    mov    abswriteseg,ax
;
    mov    ax,savkeepoff
    mov    keepoff,ax
    mov    ax,savkeepseg
    mov    keepseg,ax
;
    sti
;
        pop     es
    ret
;
    assume    es:nothing
;
_tsk_remove_dos    endp
;
;
;---------------------------------------------------------------------------
;
;    Stack-Offsets relative to BP
;
caller_cs    =    4        ; Caller's CS
caller_flags    =    6        ; Caller's Flags
;
;
;---------------------------------------------------------------------------
;
;    INT 25: Absolute Disk Read
;
;    This interrupt is translated into INT 21, function C0.
;    This function is re-translated later after the necessary resources
;    have been requested.
;
absread_int:
    mov    ah,0c0h
    jmp    short absrw_int
;
;
;---------------------------------------------------------------------------
;
;    INT 26: Absolute Disk Write
;
;    This interrupt is translated into INT 21, function C1.
;    This function is re-translated later after the necessary resources
;    have been requested.
;
abswrite_int:
    mov    ah,0c1h
;
;    Interrupts 25 und 26 leave the flag-word on the stack.
;    Since flags are removed in normal processing, the flag-word
;    has to be duplicated on the stack here.
;
absrw_int:
    push    bp            ; reserve space
    push    bp            ; save BP
    mov    bp,sp
    sti
    push    ax
    mov    ax,4[bp]        ; Move return offset, segment down
    mov    2[bp],ax
    mov    ax,6[bp]
    mov    4[bp],ax
    mov    ax,8[bp]        ; duplicate flags
    mov    6[bp],ax
    pop    ax
    push    caller_flags[bp]
    jmp    short dosentry_2
;
;---------------------------------------------------------------------------
;
;    INT 27: Terminate But Stay Resident Interrupt
;
;    This interrupt is translated to INT 21, function 31.
;
keep_int:
    push    bp
    mov    bp,sp
    push    caller_flags[bp]    ; flags (bp-2)
    sti                ; allow interrupts
;
    add    dx,0fh            ; last addr + 0f to round
    sub    dx,caller_cs[bp]    ; minus CS (= PSP)
    mov    cl,4
    shr    dx,cl            ; div 16 = paragraphs

    mov    ax,3100h        ; Keep process
    jmp    short dosentry_2
;
;---------------------------------------------------------------------------
;
;    INT 20: Terminate Program interrupt
;
;    This interrupt is translated to INT 21, function 0.
;
terminate_int:
    mov    ah,0
;
;    fall through
;
;---------------------------------------------------------------------------
;
;    INT 21: DOS-Interrupt
;
dosentry        proc    far
;
;    Save registers
;
    push    bp
    mov    bp,sp
    push    caller_flags[bp]    ; flags (bp-2)
;
dosentry_2:
    push    es
    push    ds
    push    dx
    push    cx
    push    bx
    push    ax
    push    si
    push    di
    cld
    mov    bx,SEG dgroup
    mov    ds,bx
    mov    es,bx
;
;
;    Here we check if the DOS critical region is active.
;    If yes, this means that some outside background process has
;    started DOS (most likely DOS PRINT).
;    To avoid busy waiting, we wait for the "critical" flag to be
;    cleared, if this is *not* the task that set the flag.
;    The task that set the critical task is *not* made waiting.
;
wait_crit_loop:
    cli
    cmp    cs:critsect_active,0
    je    no_crit
    mov    ax,word ptr cs:crit_task
    cmp    word ptr _tsk_current,ax
    jne    wait_crit
    mov    ax,word ptr cs:crit_task+2
    cmp    word ptr _tsk_current+2,ax
    je    no_crit
;
wait_crit:
    xor    ax,ax
    push    ax
    push    ax
        mov     ax,offset _critical
    push    ds
    push    ax
        call    _asm_wait_flag_clear
    add    sp,8
;
no_crit:
    mov    cs:ctask_active,1    ; mark that we are active
    sti                ; Interrupts allowed now
;
        cmp     ah,4ch                  ; terminate?
        jne     dosent_x
        mov     ah,0                    ; translate to fn 0
dosent_x:
    cmp    ah,0ch
    jbe    lower_funcs
    jmp    upper_funcs
;
;    Functions 00-0C
;
lower_funcs:
;
;    first, request the "lower_dos" resource
;
        mov     bx,offset _lower_dos
    xor    cx,cx
    push    cx        ; no timeout
    push    cx
    push    ds        ; resource address
    push    bx
        call    _asm_request_resource
    add    sp,8
;
;    we have it, now let's get the upper_dos resource, too
;
        mov     bx,offset _upper_dos
    xor    cx,cx
    push    cx        ; no timeout
    push    cx
    push    ds        ; resource address
    push    bx
        call    _asm_request_resource
    add    sp,8
;
;    both resources gained, now we may execute the function if dos is free
;
    pop    di
    pop    si
    pop    ax
    pop    bx
    pop    cx
    pop    dx
;
    call    wait_dos_free
;
    or    ah,ah            ; terminate ?
    je    fg_terminate        ; special treatment required
    cmp    ah,4ch
    je    fg_terminate        ; special treatment required
    pop     ds
    pop    es
    popf
    pop    bp
;
    dos                ; execute function
;
;    Now we have to release the resources.
;
    pushf                ; save registers again
    sti
    push    es
    push    ds
    push    dx
    push    cx
    push    bx
    push    ax
    push    si
    push    di
;
    mov    bx,SEG dgroup
    mov    ds,bx
    mov    es,bx
;
        mov     bx,offset _upper_dos
    push    ds        ; resource address
    push    bx
        call    _asm_release_resource
    add    sp,4
;
        mov     bx,offset _lower_dos
    push    ds        ; resource address
    push    bx
        call    _asm_release_resource
    add    sp,4
;
;    If both resources are free now, clear the ctask_active flag to
;    allow other background processes to gain access to DOS.
;
    cli
        mov     ax,_upper_dos.rstate
        or    ax,ax
        jz    no_relc
        cmp     ax,_lower_dos.rstate
    jne    no_relc
    mov    cs:ctask_active,0
no_relc:
;
;    All done, restore registers and return.
;
    pop    di
    pop    si
    pop    ax
    pop    bx
    pop    cx
    pop    dx
    pop     ds
    pop    es
    popf
;
    ret    2            ; don't restore flags
;
;
;    The terminate request requires special treatment.
;    Since terminating the program without first un-installing
;    would crash the system, we do this here, not without telling
;    the user something went very wrong.
;
fg_terminate:
    cli
    call    _asm_remove_tasker
    mov    dx,offset term_err_msg
    mov    ah,9
    int    21h
    mov    ax,4cffh
    int    21h
;
;--------------------------------------------------------------------------
;
;    Functions 0D and above
;
upper_funcs:
        mov     bx,offset _upper_dos
    xor    cx,cx
    push    cx        ; no timeout
    push    cx
    push    ds        ; resource address
    push    bx
        call    _asm_request_resource
    add    sp,8
;
;    resource gained, now we may execute the function if dos is free
;
    pop    di
    pop    si
    pop    ax
    pop    bx
    pop    cx
    pop    dx
;
    call    wait_dos_free
;
    pop     ds
    pop    es
;
;
;    Filter pseudo-functions C0/C1 (Absolute Read/Write)
;
    cmp    ah,0c0h
    jne    uf_exec1
    popf
    pop    bp
    call    exec_absread
    jmp    short uf_complete
uf_exec1:
    cmp    ah,0c1h
    jne    uf_exec2
    popf
    pop    bp
    call    exec_abswrite
    jmp    short uf_complete
;
uf_exec2:
    popf
    pop    bp
    dos                ; execute function
;
;    Now we have to release the resources.
;
uf_complete:
    pushf                ; save registers again
    sti
    push    es
    push    ds
    push    dx
    push    cx
    push    bx
    push    ax
    push    si
    push    di
;
    mov    bx,SEG dgroup
    mov    ds,bx
    mov    es,bx
;
        mov     bx,offset _upper_dos
    push    ds        ; resource address
    push    bx
        call    _asm_release_resource
    add    sp,4
;
;    If both resources are free now, clear the ctask_active flag to
;    allow other background processes to gain access to DOS.
;
    cli
        mov     ax,_upper_dos.rstate
        or    ax,ax
        jz    no_relc1
        cmp     ax,_lower_dos.rstate
    jne    no_relc1
    mov    cs:ctask_active,0
no_relc1:
;
;    All done, restore registers and return.
;
    pop    di
    pop    si
    pop    ax
    pop    bx
    pop    cx
    pop    dx
    pop     ds
    pop    es
    popf
;
    ret    2            ; don't restore flags
;
;
dosentry    endp
;
;--------------------------------------------------------------------------
;
;    Absolute Read/Absolute Write.
;
exec_absread    proc    near

    pushf
    call    cs:savabsread
    inc    sp            ; Remove flags (not using ADD,
    inc    sp            ; this would clobber Carry)
    ret

exec_absread    endp
;
exec_abswrite    proc    near

    pushf
    call    cs:savabswrite
    inc    sp            ; Remove flags (not using ADD,
    inc    sp            ; this would clobber Carry)
    ret

exec_abswrite    endp
;
;----------------------------------------------------------------------------
;
wait_dos_free    proc    near
;
    push    es
    push    bx
in_use_loop:
    cmp    idle_active,0        ; idle interrupt active?
    jne    dos_free        ; then don't check for flag
;
    les    bx,in_use
    cmp    byte ptr es:[bx],0
    jne    is_in_use
    cmp    dos310,0
    je    dos_free
    les    bx,in_error
    cmp    byte ptr es:[bx],0
    je    dos_free
is_in_use:
    pushf
    call    scheduler
    jmp    in_use_loop
;
dos_free:
    pop    bx
    pop    es
    ret
;
wait_dos_free    endp
;
;----------------------------------------------------------------------------
;
;    INT 28: DOS Idle Interrupt
;
idleentry    proc    far
;
    push    ds
    push    es
    push    ax
;
    mov    ax,SEG dgroup
    mov    ds,ax
    mov    es,ax
;
;    Check if someone is waiting for upper_dos. If not, we can return
;    immediately.
;
        mov     ax,word ptr _upper_dos.rwaiting
        or      ax,word ptr _upper_dos.rwaiting+2
    jz    idle_exit
;
;    Also make sure this is not a second invocation of INT 28.
;    Normally, this should never happen, but better safe than sorry.
;
    cmp    idle_active,0
    jne    idle_exit
    inc    idle_active
;
;    someone is waiting, let's please him by releasing the resource
;
    mov    idle_ss,ss        ; Switch to local stack
    mov    idle_sp,sp
    mov    ax,ds
    mov    ss,ax
    mov    sp,offset local_stack
;
    sti                ; Interrupts allowed now
;
        push    bx            ; save remaining regs
    push    cx
    push    dx
;
;    temporarily increase priority
;
    les    bx,_tsk_current
    push    es:prior[bx]
    mov    es:prior[bx],0ffffh
    push    bx
    push    es
;
;    release resource & request it again
;
    mov    ax,ds
    mov    es,ax
        mov     bx,offset _upper_dos
    push    ds
    push    bx
        call    _asm_release_resource
    add    sp,4
;
        mov     bx,offset _upper_dos
    xor    cx,cx
    push    cx
    push    cx
    push    ds
    push    bx
        call    _asm_request_resource
    add    sp,8
;
;    ready, restore priority, stack & regs
;
    cli
    pop    es
    pop    bx
    pop    es:prior[bx]
;
    pop    dx
    pop    cx
    pop    bx
;
    mov    ss,idle_ss        ; restore stack
    mov    sp,idle_sp
;
    mov    idle_active,0
;
idle_exit:
    pop    ax
        pop     es
    pop    ds
;
    jmp    cs:savidle        ; chain to original interrupt
;
idleentry    endp
;
;---------------------------------------------------------------------------
;
;    INT 2A: DOS Critical Section Interrupt.
;
;    Not documented.
;    Is used by DOS PRINT to mark Critical Regions.
;    Usage by PRINT:
;        AX = 8700 - Begin Critical Region
;                Returns:
;                Carry set if already active.
;        AX = 8701 - End Critical Region
;
;    Both these functions are handled here.
;
;    Other usage in DOS, function unknown:
;        AH = 82 (AL undefined)
;            seems to be called on DOS-Functions > 0C
;        AH = 84 (AL undefined)
;            seems to be called when DOS is idle
;
;    These functions are currently ignored.
;
critsectint    proc    far

    cmp    ax,8700h    ; Enter critical region
    jne    csi1
    cmp    cs:critsect_active,0
    stc
    jnz    critsect_end
    cmp    cs:ctask_active,0
    stc
    jnz    critsect_end
;
    inc    cs:critsect_active
    push    ax
    push    bx
    push    cx
    push    dx
    push    ds
    push    es
    mov    ax,seg dgroup
    mov    ds,ax
    mov    es,ax
    mov    ax,word ptr _tsk_current
    mov    word ptr cs:crit_task,ax
    mov    ax,word ptr _tsk_current+2
    mov    word ptr cs:crit_task+2,ax
        mov     ax,offset _critical
    push    ds
    push    ax
    call    _asm_set_flag
    add    sp,4
    pop    es
    pop    ds
    pop    dx
    pop    cx
    pop    bx
    pop    ax
    clc
critsect_end:
    ret    2
;
csi1:
    cmp    ax,8701h    ; Leave critical region
    jne    csi2
    mov    cs:critsect_active,0
    push    ax
    push    bx
    push    cx
    push    dx
    push    ds
    push    es
    mov    ax,seg dgroup
    mov    ds,ax
    mov    es,ax
        mov     ax,offset _critical
    push    ds
    push    ax
        call    _asm_clear_flag
    add    sp,4
    pop    es
    pop    ds
    pop    dx
    pop    cx
    pop    bx
    pop    ax
csi2:
    iret
;
critsectint    endp
;
;
;---------------------------------------------------------------------------
;
        end