C/C++ Users Group Library 1996 July/C-C++ Users Group Library July 1996.iso/vol_300/330_03/tskdos.asm

Assembly Source File | 1990-10-10 | 35.4 KB | 1,587 lines

;
;    --- Version 2.2 90-10-12 10:37 ---
;
;    CTask - DOS access module.
;
;    Public Domain Software written by
;        Thomas Wagner
;        Ferrari electronic Gmbh
;        Beusselstrasse 27
;        D-1000 Berlin 21
;        Germany
;
; NOTE: Some routines have been moved to "tsksec.asm" in Version 2.1
;    to support a minimal secondary kernel.
;
;    The support for the critical section interrupt was dropped in
;    version 2.1. Swapping the DOS variable area eliminates
;    the need for maintaining critical sections across calls.
;
; 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 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.
;
; CAUTION:    This module is not ROMable, and it can only be
;        installed in the primary kernel.
;
    name    tskdos
;
    include    tsk.mac
;
    IF    DOS
;
    .tsk_model
;
    include    tskdeb.h
;
    Pubfunc    tsk_install_dos
    Pubfunc    tsk_remove_dos
    Pubfunc    tsk_fatal
    IF    CHECKING
    Pubfunc    tsk_fatal_pmd
    Globext    tsk_set_currdis
    Globext    tsk_set_dualdis
    Globext    tsk_rputc
    Globext    tsk_rputs
    Globext    tsk_vrprintf
    CGlbext    tsk_rprintf
    ENDIF
;
    public    tsk_emergency_exit
;
    Globext    create_resource
    Globext    delete_resource
    Globext    request_resource
    Globext    request_cresource
    Globext    release_resource
    Globext    create_flag
    Globext    delete_flag
    Globext    set_flag
    Globext    clear_flag
    Globext    wait_flag_clear
    Globext    yield
    Globext    preempt_off
;
    Locext    tsk_switch_stack
    Locext    tsk_old_stack
    Locext    tsk_remove_group
    Locext    tsk_kill_group
    Locext    tsk_remove_tasker
;
    extrn    tsk_instflags: word
;
    extrn    tsk_glob_rec: byte
    IF    NOT SINGLE_DATA
    extrn    tsk_global: dword
    ENDIF
;
get_in_use_flag    =    34h    ; DOS-function to get in_use_flag address
get_invars    =    5d06h    ; DOS-function to get DOS-variables area
;
psp_offset    =    10h-2    ; Offset of current PSP in DOS save area
;                ; (-2 because we add 2 to the start)
;
;    Structure of the start of a PSP, including undocumented fields
;
psp_record    struc
;
        dw    ?    ; INT 20
        dw    ?    ; alloc block end
        db    ?    ; reserved
        db    5 dup(?) ; system call
psp_exit_addr    dd    ?    ; exit routine address
psp_ctlc_addr    dd    ?    ; control C routine address
psp_cerr_addr    dd    ?    ; critical error routine address
parent_psp    dw    ?    ; PSP of parent process
        db    20 dup(?) ; files table
psp_envseg    dw    ?    ; environment segment
psp_ustack    dd    ?    ; ss/sp of caller
        dw    ?    ; file table length
        dd    ?    ; file table pointer
        dd    ?    ; pointer to nested PSP (?)
;
psp_record    ends
;
;
intseg    segment at 0
        org    10h*4
vidoff        dw    ?    ; video interrupt
vidseg        dw    ?
        org    13h*4
diskoff        dw    ?    ; disk i/o interrupt
diskseg        dw    ?
        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    2ah*4
csectoff    dw    ?    ; dos critical section
csectseg    dw    ?
        org    40h*4
fdiskoff    dw    ?    ; redirected floppy disk I/O interrupt
fdiskseg     dw    ?
;
intseg    ends
;
;----------------------------------------------------------------------------
;
;    Variables
;
    .tsk_data
;
idle_active    db    0            ; Idle-Interrupt active
dos310        db    0        ; DOS version >= 3.10
;
    IF    TSK_NAMEPAR
udos_name    db    "DOSUPPER",0
ldos_name    db    "DOSLOWER",0
hdio_name    db    "HARDDISK",0
fdio_name    db    "FLEXDISK",0
vid_name    db    "VIDEO",0
    ENDIF
;
;
in_error    dd    ?        ; Adress of DOS error-mode-flag
;
lower_dos    resource <>
upper_dos    resource <>
hdisk_io    resource <>
fdisk_io    resource <>
video        resource <>
;
vid_flags    dw    ?
i13h_flags    dw    ?
i13f_flags    dw    ?
;
    .tsk_edata
    .tsk_code
;
;---------------------------------------------------------------------------
;
;    Original Interrupt-Entries
;
savvid        label    dword        ; original Video entry
savvidoff    dw    ?
savvidseg    dw    ?
;
savdisk        label    dword        ; original Disk I/O entry
savdiskoff    dw    ?
savdiskseg    dw    ?
;
savfdisk     label    dword        ; original Floppy Disk I/O entry
savfdiskoff    dw    ?
savfdiskseg    dw    ?
;
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    ?
;
;
dos_version    dw    ?        ; DOS version
;
temp_1        dw    ?
;
tsk_dgroup    dw    @CTASK_DATA
;
zero        db    0
;
calldos    macro
    pushf
    cli
    call    cs:savdos
    endm
;
;---------------------------------------------------------------------------
;
;    void tsk_install_dos (void)
;
;        Install DOS handler
;
Localfunc tsk_install_dos
;
;    create needed resources & flags
;
    IFDEF    LOAD_DS
    push    ds
    mov    ax,@CTASK_DATA
    mov    ds,ax
    ENDIF
;
    IF    TSK_NAMEPAR
    callp    create_resource,<<ds,#upper_dos>,<ds,#udos_name>>
    ELSE
    callp    create_resource,<<ds,#upper_dos>>
    ENDIF
;
    IF    TSK_NAMEPAR
    callp    create_resource,<<ds,#lower_dos>,<ds,#ldos_name>>
    ELSE
    callp    create_resource,<<ds,#lower_dos>>
    ENDIF
;
    test    tsk_instflags,IFL_DISK
    jz    inst_nodsk1
    IF    TSK_NAMEPAR
    callp    create_resource,<<ds,#hdisk_io>,<ds,#hdio_name>>
    ELSE
    callp    create_resource,<<ds,#hdisk_io>>
    ENDIF
;
    IF    TSK_NAMEPAR
    callp    create_resource,<<ds,#fdisk_io>,<ds,#fdio_name>>
    ELSE
    callp    create_resource,<<ds,#fdisk_io>>
    ENDIF
;
inst_nodsk1:
    test    tsk_instflags,IFL_VIDEO
    jz    inst_novid1
    IF    TSK_NAMEPAR
    callp    create_resource,<<ds,#video>,<ds,#vid_name>>
    ELSE
    callp    create_resource,<<ds,#video>>
    ENDIF
;
inst_novid1:
;
    mov    tsk_glob_rec.l_swap,0    ; init swap area length to 0
;
;    Get the DOS version. Only versions 3.1 and up support the
;    DOS variable swap, so disable swapping if it's an earlier version,
;    or if it's the OS/2 box.
;
    mov    ah,30h
    int    21h
    mov    cs:dos_version,ax
    cmp    al,3
    jb    not_dos3
    cmp    al,0ah
    je    not_dos3    ; OS/2 compatibility box
        cmp     al,3
        jne     is_dos3         ; DOS 4.x
    cmp    ah,10
    jb    not_dos3
is_dos3:
    inc    dos310
;
;    Get address and length of the DOS internal variable area.
;    This call is not documented, and not available in versions
;    prior to 3.1. It returns the address of the area in DS:SI,
;    and the length of the area that must be swapped between calls
;    from different groups in DX.
;    Additionally, the total length of the area, including
;    the DOS-stacks, minus the length in DX, is returned in CX.
;
;    The DOS in_error flag is at the start of this area, the
;    in_use flag is the second byte. Both bytes are excluded
;    from the swap.
;
    test    tsk_instflags,IFL_NODOSVARS
    jnz    not_dos3
;
    push    ds
    mov    ax,get_invars
    int    21h
    mov    ax,ds
    pop    ds
    mov    word ptr in_error,si
    mov    word ptr in_error+2,ax
    inc    si
    mov    word ptr tsk_glob_rec.dos_in_use,si
    mov    word ptr tsk_glob_rec.dos_in_use+2,ax
    inc    si
    mov    word ptr tsk_glob_rec.dos_vars,si
    mov    word ptr tsk_glob_rec.dos_vars+2,ax
    sub    dx,2
    mov    tsk_glob_rec.l_swap,dx
    jmp    short save_ints
;
;    For versions < 3.10, and if the IFL_NODOSVARS flag is set,
;    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.
;
not_dos3:
    mov    ah,get_in_use_flag
    int    21h
    mov    word ptr tsk_glob_rec.dos_in_use,bx
    mov    word ptr tsk_glob_rec.dos_in_use+2,es
    mov    word ptr in_error+2,es
    dec    bx
    mov    word ptr in_error,bx
    cmp    dos310,0
    jne    save_ints        ; OK for DOS >= 3.10
;
;    For DOS < 3.1, we simply ignore the error flag.
;    CTask's DOS handler will not work that great anyway with older
;    versions.
;
    mov    word ptr in_error,offset zero
    mov    word ptr in_error+2,cs
;
;    Save old interrupt vectors
;
save_ints:
        push    es
    xor    ax,ax
    mov    es,ax
;
        assume  es:intseg
;
    test    tsk_instflags,IFL_VIDEO
    jz    inst_novid2
    mov    ax,vidoff        ; video
    mov    savvidoff,ax
    mov    ax,vidseg
    mov    savvidseg,ax
;
inst_novid2:
    test    tsk_instflags,IFL_DISK
    jz    inst_nodsk2
    mov    ax,diskoff        ; Disk I/O
    mov    savdiskoff,ax
    mov    ax,diskseg
    mov    savdiskseg,ax
    mov    ax,fdiskoff        ; Floppy Disk I/O
    mov    savfdiskoff,ax
    mov    ax,fdiskseg
    mov    savfdiskseg,ax
;
inst_nodsk2:
    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
    test    tsk_instflags,IFL_VIDEO
    jz    inst_novid3
    mov    vidoff,offset @videntry        ; Video Entry
    mov    vidseg,cs
;
inst_novid3:
    test    tsk_instflags,IFL_DISK
    jz    inst_nodsk3
    mov    diskoff,offset @diskentry    ; Disk I/O Entry
    mov    diskseg,cs
    mov    fdiskoff,offset @fdiskentry    ; Floppy Disk I/O Entry
    mov    fdiskseg,cs
;
inst_nodsk3:
    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
;
    assume    es:nothing
;
        pop     es
    IFDEF    LOAD_DS
    pop    ds
    ENDIF
    ret
;
;
tsk_install_dos    endp
;
;---------------------------------------------------------------------------
;
;    void tsk_remove_dos (void)
;
;        Un-install DOS handler
;
Localfunc tsk_remove_dos
;
    IFDEF    LOAD_DS
    push    ds
    mov    ax,@CTASK_DATA
    mov    ds,ax
    ENDIF
;
;    Delete resources & flags
;
    callp    delete_resource,<<ds,#upper_dos>>
    callp    delete_resource,<<ds,#lower_dos>>
;
    test    tsk_instflags,IFL_DISK
    jz    rem_nodsk1
    callp    delete_resource,<<ds,#hdisk_io>>
    callp    delete_resource,<<ds,#fdisk_io>>
;
rem_nodsk1:
    test    tsk_instflags,IFL_VIDEO
    jz    rem_novid1
    callp    delete_resource,<<ds,#video>>
;
rem_novid1:
        push    es
    xor    ax,ax
    mov    es,ax
;
        assume  es:intseg
;
;    Restore interrupt entries
;
    cli
    test    tsk_instflags,IFL_VIDEO
    jz    rem_novid2
    mov    ax,savvidoff
    mov    vidoff,ax
    mov    ax,savvidseg
    mov    vidseg,ax
;
rem_novid2:
    test    tsk_instflags,IFL_DISK
    jz    rem_nodsk2
    mov    ax,savdiskoff
    mov    diskoff,ax
    mov    ax,savdiskseg
    mov    diskseg,ax
    mov    ax,savfdiskoff
    mov    fdiskoff,ax
    mov    ax,savfdiskseg
    mov    fdiskseg,ax
;
rem_nodsk2:
    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
    IFDEF    LOAD_DS
    pop    ds
    ENDIF
    ret
;
    assume    es:nothing
;
tsk_remove_dos    endp
;
;
;---------------------------------------------------------------------------
;---------------------------------------------------------------------------
;
;
;    INT 10: Video BIOS interrupt
;
@videntry    proc    far
;
    call    tsk_switch_stack
    callp    request_cresource,<<ds,#video>,0,0>
    mov    ax,caller_flags[bp]
    mov    vid_flags,ax
    call    tsk_old_stack
    pushf
    cli
    call    savvid
    call    tsk_switch_stack
    mov    ax,vid_flags
    mov    caller_flags[bp],ax
    callp    release_resource,<<ds,#video>>
    iret
;
@videntry    endp
;
;---------------------------------------------------------------------------
;
;
;    INT 13 and INT 40: Disk I/O BIOS interrupt
;
@diskentry    proc    far
;
    call    tsk_switch_stack
    test    dl,80h            ; fixed disk ?
    jz    disk_floppy        ; jump if not
    callp    request_cresource,<<ds,#hdisk_io>,0,0>
    call    tsk_old_stack
    pushf
    cli
    call    savdisk
    call    tsk_switch_stack
    callp    release_resource,<<ds,#hdisk_io>>
    mov    ax,entry_flags[bp]
    mov    caller_flags[bp],ax
    iret
;
disk_floppy:
    callp    request_cresource,<<ds,#fdisk_io>,0,0>
    call    tsk_old_stack
    pushf
    cli
    call    savdisk
    call    tsk_switch_stack
    callp    release_resource,<<ds,#fdisk_io>>
    mov    ax,entry_flags[bp]
    mov    caller_flags[bp],ax
    iret
;
@diskentry    endp
;
@fdiskentry    proc    far
;
    call    tsk_switch_stack
    callp    request_cresource,<<ds,#fdisk_io>,0,0>
    call    tsk_old_stack
    pushf
    cli
    call    savfdisk
    call    tsk_switch_stack
    callp    release_resource,<<ds,#fdisk_io>>
    mov    ax,entry_flags[bp]
    mov    caller_flags[bp],ax
    iret
;
@fdiskentry    endp
;
;---------------------------------------------------------------------------
;
;    Stack-Offsets relative to BP
;
d_func    =    -2
;
;---------------------------------------------------------------------------
;
;    INT 25: Absolute Disk Read
;
;    This interrupt is channeled through the normal DOS-function
;    processing, with function = 0x25 and special flag set.
;    It is re-translated later after the necessary resources
;    have been requested. INT 25 is handled like a function > 0C.
;    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.
;
absread_int:
    sti
    push    bp            ; reserve space
    push    bp            ; save BP
    mov    bp,sp
    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
    pop    bp
    call    tsk_switch_stack
    mov    ax,2501h
    mov    cx,ax
    jmp    short dosentry_2
;
;
;---------------------------------------------------------------------------
;
;    INT 26: Absolute Disk Write
;
;    This interrupt is channeled through the normal DOS-function
;    processing, with function = 0x26 and special flag set.
;    It is re-translated later after the necessary resources
;    have been requested. INT 26 is handled like a function > 0C.
;    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.
;
abswrite_int:
    sti
    push    bp            ; reserve space
    push    bp            ; save BP
    mov    bp,sp
    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
    pop    bp
    call    tsk_switch_stack
    mov    ax,2601h
    mov    cx,ax
    jmp    short dosentry_2
;
;---------------------------------------------------------------------------
;
;    INT 27: Terminate But Stay Resident Interrupt
;
;    This interrupt is translated to INT 21, function 31.
;
keep_int:
    call    tsk_switch_stack
;
    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
    mov    save_ax[bp],ax
    mov    cx,ax
    jmp    short dosentry_2
;
;---------------------------------------------------------------------------
;
;    INT 20: Terminate Program interrupt
;
;    This interrupt is translated to INT 21, function 4c.
;
terminate_int:
    call    tsk_switch_stack
    mov    ax,4c00h
    mov    save_ax[bp],ax
    mov    cx,ax
    jmp    short dosentry_2
;
;---------------------------------------------------------------------------
;
;    INT 21: DOS-Interrupt
;
@dosentry        proc    far
;
    call    tsk_switch_stack
    xor    cl,cl
    mov    ch,ah
;
dosentry_2:
    push    cx        ; BP-2: func in CH, special flag in CL
    or    cl,cl
    jnz    dosent_x    ; no function check if special
;
;    Check if this is a special 'get dos version' call to determine
;    if CTask is resident.
;
;    A special call has
;
;        AX = 3000h
;        BX = 1234h
;        DS:DX = pointer to version string
;
    cmp    ax,3000h
    jne    no_spdos
    cmp    bx,1234h
    jne    no_spdos
    cmp    dx,0fff0h
    jae    no_spdos
    push    ds
    mov    si,dx
    mov    ds,save_ds[bp]
    mov    di,offset tsk_glob_rec
    mov    cx,8
    repe cmpsb
    pop    ds
    jz    is_spdos
    jmp    short no_spdos
;
;    Special version call returns global variable block address
;    in BX (offset) and CX (segment).
;
is_spdos:
    add    sp,2
    call    tsk_old_stack
    mov    ax,cs:dos_version
    mov    bx,offset tsk_glob_rec
    mov    cx,@CTASK_DATA
    iret
;
;---------------------------------------------------------------------------
;
;
no_spdos:
    mov    ax,d_func[bp]
        or    ah,ah            ; terminate?
        jne     dosent_x
        mov     save_ax[bp],4c00h    ; translate to fn 4c, retcode 0
        mov     d_func[bp],4c00h
;
;    Now the real fun begins.
;
dosent_x:
    sti                ; Interrupts allowed now
;
;    DL is used as an "emergency" marker. If nonzero, no resources
;    are to be requested, and the in-dos flag is not to be checked.
;    There is an "emergency" if the task is marked as owning
;    DOS resources, but re-enters INT 21.
;
    xor    dl,dl
    les    bx,tsk_glob_rec.current_task
    test    es:t_indos[bx],OWN_UPPER OR OWN_LOWER
    jz    no_reenter        ; no trouble if task doesn't own DOS
;
    call    @dosbusy        ; this sets DL nonzero if busy
    jnz    no_reenter        ; Don't release resources if busy
;
;    If the task owns DOS resources, but DOS is not busy, something
;    strange is going on (this case should have been handled by the
;    'schedent' routine). Anyway, we assume that DOS is right about
;    not being busy, and release the resources. Although the resources
;    will be requested again a few instructions later, this is sensible
;    to give other tasks that might be waiting on the resource a chance
;    to execute.
;
    call    @relres
    xor    dl,dl
;
;    The preliminaries are done with, we now have to distinguish
;    between functions 00-0C and 0D-FF.
;
no_reenter:
    mov    ax,d_func[bp]
    cmp    ah,0ch
    jbe    lower_funcs
    jmp    upper_funcs
;
;
;    Functions 00-0C
;
lower_funcs:
;
;    first, request the "lower_dos" resource unless this is an emergency.
;
    or    dl,dl
    jnz    lower_emergency
    callp    request_resource,<<ds,#lower_dos>,0,0>
;
;    we have it, now let's get the upper_dos resource, too
;
    callp    request_resource,<<ds,#upper_dos>,0,0>
;
    les    bx,tsk_glob_rec.current_task
    mov    es:t_indos[bx],OWN_UPPER or OWN_LOWER
;
;    both resources gained, now we may execute the function if dos is free
;
    call    @wait_dos_free
;
;    Set the scheduler entry function
;
    cli
    mov    word ptr es:sched_ent_func[bx],offset @schedent
    mov    word ptr es:sched_ent_func+2[bx],cs
    sti
;
lower_emergency:
    add    sp,2
    push    caller_flags[bp]
    popf
    call    tsk_old_stack
;
    calldos                ; execute function
;
;    Now we have to release the resources, unless DOS still indicates
;    that it is busy. This would indicate that a critical error has
;    occurred, and DOS processing is not really complete.
;
    call    tsk_switch_stack
;
    call    @dosbusy
    jnz    no_relc            ; return if DOS still busy
;
;    Clear the flags in the TCB, and the scheduler entry function.
;
    les    bx,tsk_glob_rec.current_task
    cli
    mov    es:t_indos[bx],0
    mov    word ptr es:sched_ent_func[bx],0
    mov    word ptr es:sched_ent_func+2[bx],0
    sti
;
    callp    release_resource,<<ds,#upper_dos>>
    callp    release_resource,<<ds,#lower_dos>>
;
;    All done, restore registers and return.
;
no_relc:
    cli
    mov    ax,entry_flags[bp]
    mov    caller_flags[bp],ax
    iret
;
;--------------------------------------------------------------------------
;
;    Functions 0D and above
;
upper_funcs:
;
;    first, request the "upper_dos" resource unless this is an emergency.
;
    or    dl,dl
    jnz    upper_emergency
;
    callp    request_resource,<<ds,#upper_dos>,0,0>
;
    les    bx,tsk_glob_rec.current_task
    mov    es:t_indos[bx],OWN_UPPER
;
;    resource gained, now we may execute the function if dos is free
;
    call    @wait_dos_free
;
;    Set the scheduler entry function
;
    cli
    mov    word ptr es:sched_ent_func[bx],offset @schedent
    mov    word ptr es:sched_ent_func+2[bx],cs
    sti
;
upper_emergency:
    cmp    byte ptr d_func[bp],0
    jne    no_term
    mov    ax,save_ax[bp]
    cmp    ah,31h        ; terminate resident?
    jne    ckfunc1
    jmp    term_resident
ckfunc1:
    cmp    ax,4b00h    ; spawn new process?
    jne    ckfunc2
    jmp    terminate
ckfunc2:
    cmp    ah,4ch        ; terminate program?
    jne    no_term
    jmp    terminate
;
no_term:
;
;    Filter special-functions 25/26 (Absolute Read/Write)
;
    pop    ax
    cmp    ax,2501h
    jne    uf_exec1
    push    caller_flags[bp]
    popf
    call    tsk_old_stack
    pushf
    cli
    call    cs:savabsread
    pop    cs:temp_1        ; remove flags
    jmp    short uf_complete
;
uf_exec1:
    cmp    ax,2601h
    jne    uf_exec2
    push    caller_flags[bp]
    popf
    call    tsk_old_stack
    pushf
    cli
    call    cs:savabswrite
    pop    cs:temp_1        ; remove flags
    jmp    short uf_complete
;
uf_exec2:
    push    caller_flags[bp]
    popf
    call    tsk_old_stack
;
    calldos                ; execute function
;
;    Now we have to release the resources, unless DOS still indicates
;    that it is busy. This would indicate that a critical error has
;    occurred, and DOS processing is not really complete.
;    However, if we were called from INT 28, DOS must still be busy,
;    so we only check the in_error flag.
;
uf_complete:
    call    tsk_switch_stack
;
    cmp    idle_active,0
    jnz    uf_nobsychk        ; don't check busy if INT 28 call
    les    bx,tsk_glob_rec.dos_in_use
    cmp    es:byte ptr [bx],0
    jne    no_relc_uf        ; don't release if busy
;
uf_nobsychk:
    les    bx,in_error
    cmp    es:byte ptr [bx],0
    jnz    no_relc_uf        ; don't release if in error
;
    les    bx,tsk_glob_rec.current_task
    cli
    mov    es:t_indos[bx],0
    mov    word ptr es:sched_ent_func[bx],0
    mov    word ptr es:sched_ent_func+2[bx],0
    sti
;
    callp    release_resource,<<ds,#upper_dos>>
;
;    All done, restore registers and return.
;
no_relc_uf:
    cli
    mov    ax,entry_flags[bp]
    mov    caller_flags[bp],ax
    iret
;
;--------------------------------------------------------------------------
;
;    Terminate, TSR and Spawn calls go directly to DOS.
;    TSR has to reset the exit address if it's the PSP of the
;    current group, so the group is not deleted.
;
term_resident:
    les    bx,tsk_glob_rec.dos_vars
    mov    ax,es:[bx+psp_offset]        ; current PSP
    les    bx,tsk_glob_rec.current_task
    les    bx,es:tgroup[bx]
    cmp    es:gcreate_psp[bx],ax
    jne    terminate
    push    ds
    mov    ds,ax
    mov    ax,word ptr es:grp_exit_addr[bx]
    mov    word ptr ds:psp_exit_addr,ax
    mov    ax,word ptr es:grp_exit_addr+2[bx]
    mov    word ptr ds:psp_exit_addr+2,ax
    pop    ds
;
terminate:
    add    sp,2
    push    caller_flags[bp]
    popf
    call    tsk_old_stack
    cli
    jmp    cs:savdos
;
@dosentry    endp
;
;--------------------------------------------------------------------------
;
;    'dosbusy' checks the DOS busy flags.
;
;    Entry:    -
;    Exit:    DL is nonzero if DOS is busy.
;
@dosbusy    proc    near
;
    push    bx
    push    es
    les    bx,in_error
    mov    dl,es:byte ptr [bx]
    les    bx,tsk_glob_rec.dos_in_use
    or    dl,es:byte ptr [bx]
    pop    es
    pop    bx
    ret
;
@dosbusy    endp
;
;--------------------------------------------------------------------------
;
;    Wait_dos_free uses busy waiting (calling _yield) in case
;    some other background program has entered DOS without going
;    through our INT 21 interface.
;
@wait_dos_free    proc    near
    push    es
    push    bx
;
in_use_loop:
    les    bx,in_error
    cmp    byte ptr es:[bx],0
    jne    is_in_use        ; wait if in_error set
;
    cmp    idle_active,0        ; idle interrupt active?
    je    ck_inuse        ; check for flag if no
    pop    bx
    pop    es
    ret                ; else return immediately
;
ck_inuse:
    les    bx,tsk_glob_rec.dos_in_use
    cmp    byte ptr es:[bx],0
    jne    is_in_use
    pop    bx
    pop    es
    ret
;
is_in_use:
    call    yield
    jmp    in_use_loop
;
@wait_dos_free    endp
;
;----------------------------------------------------------------------------
;
;    'relres' releases the DOS-resources of a task.
;
;    Entry:
;        ES:BX = TCB pointer
;
@relres    proc    near
;
    test    es:t_indos[bx],OWN_UPPER
    jz    rel_lower
    xor    es:t_indos[bx],OWN_UPPER
    push    bx
    push    es
    callp    release_resource,<<ds,#upper_dos>>
    pop    es
    pop    bx
;
rel_lower:
    test    es:t_indos[bx],OWN_LOWER
    jz    rel_exit
    xor    es:t_indos[bx],OWN_LOWER
    push    bx
    push    es
    callp    release_resource,<<ds,#lower_dos>>
    pop    es
    pop    bx
;
rel_exit:
    ret
;
@relres    endp
;
;----------------------------------------------------------------------------
;
;    The 'schedent' function is called by the scheduler if the
;    scheduler is entered and the current task owns one of the
;    DOS resources.
;    This routine checks whether the DOS busy flags are clear now,
;    which would mean that the task left DOS without passing through
;    the return address. If that's the case, we release the resources.
;
;    The only catch is that there is a race condition if we just check
;    the busy flags. There is a time slot where the function is set in
;    the TCB, but the busy flag is clear because DOS has not yet been
;    entered. Since we have no control over what will happen, and how
;    long it will take to reach the point where the in_use flag is
;    incremented, we can't simply disable preemption. So what we have
;    to do is to wait for some other indication that DOS has begun
;    executing the request, and mark this in the TCB. In all versions
;    starting at 3.1, DOS will call the 'critical section' INT 2A
;    with AX=8200 on functions > 0C after incrementing the in_use flag.
;    We also have some indication that DOS is active if the 'idle'
;    INT 28 is called, or if the in_use flag is set when we get here.
;
;    Entry:
;        DS    CTask data segment
;        BX    Global data block offset
;        ES:DI    Task control block
;
@schedent    proc    far
;
    call    @dosbusy        ; DOS still busy ?
    jz    schedent_relres        ; release resources if not busy
    or    es:t_indos[di],DOS_ENTERED
    ret
;
schedent_relres:
    test    es:t_indos[di],DOS_ENTERED
    jz    schedent_ret        ; don't release if DOS not yet entered
;
    mov    bx,di
    call    @relres
;
schedent_ret:
    ret
;
@schedent    endp
;
;----------------------------------------------------------------------------
;
;    INT 28: DOS Idle Interrupt
;
@idleentry    proc    far
;
    call    tsk_switch_stack
;
;    check the in_use flag. If it's set, set the DOS_ENTERED flag
;    in the current TCB.
;
    les    bx,tsk_glob_rec.dos_in_use
    cmp    byte ptr es:[bx],0
    je    no_entermark
;
    les    bx,tsk_glob_rec.current_task
    or    es:t_indos[bx],DOS_ENTERED
;
;    Check if someone is waiting for upper_dos. If not, we can return
;    immediately.
;
no_entermark:
    les    bx,upper_dos.rwaiting.q_first
    test    es:q_kind[bx],Q_HEAD
    jnz    idle_exit
;
;    Also make sure this is not a second invocation of INT 28, and
;    that the in_error flag is not set.
;    Normally, this should never happen, but better safe than sorry.
;
    cmp    idle_active,0
    jne    idle_exit
    les    bx,in_error
    cmp    byte ptr es:[bx],0
    jne    idle_exit
;
    inc    idle_active
;
;    someone is waiting, let's please him by releasing the resource.
;    temporarily increase priority
;
    les    bx,tsk_glob_rec.current_task
    push    es:cqueue.q_el.q_prior[bx]
    push    es:cqueue.q_el.q_ini_prior[bx]
    mov    es:cqueue.q_el.q_prior[bx],0ffffh
    mov    es:cqueue.q_el.q_ini_prior[bx],0ffffh
    push    bx
    push    es
;
;    release resource & request it again
;
    callp    release_resource,<<ds,#upper_dos>>
    callp    request_resource,<<ds,#upper_dos>,0,0>
;
;    ready, restore priority
;
    cli
    pop    es
    pop    bx
    pop    es:cqueue.q_el.q_ini_prior[bx]
    pop    es:cqueue.q_el.q_prior[bx]
;
    mov    idle_active,0
;
idle_exit:
    push    caller_flags[bp]
    popf
    call    tsk_old_stack
    cli
;
    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
;
;    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
;
;    We only handle function number 82 in this version,
;    it is used to mark that DOS has been entered. All functions
;    are passed on to the next in chain.
;
@critsectint    proc    far
;
    cmp    ah,82h
    jne    cs_exit
    push    ds
    push    es
    push    bx
    mov    ds,cs:tsk_dgroup
;
;    check the in_use flag. If it's set, set the DOS_ENTERED flag
;    in the current TCB.
;
    les    bx,tsk_glob_rec.dos_in_use
    cmp    byte ptr es:[bx],0
    je    cs_no_enter
;
    les    bx,tsk_glob_rec.current_task
    or    es:t_indos[bx],DOS_ENTERED
;
cs_no_enter:
    pop    bx
    pop    es
    pop    ds
;
cs_exit:
    jmp    cs:savcsect
;
@critsectint    endp
;
;---------------------------------------------------------------------------
;---------------------------------------------------------------------------
;
term_err_msg    db    0dh,0ah,"Program terminated - CTask uninstalled"
        db    0dh,0ah,'$'
;
group_term_msg    db    0dh,0ah,"Program terminated - Task Group removed"
        db    0dh,0ah,'$'
;
gcb_mixup_err    db    0dh,0ah,"Group chain damaged - System halted"
        db    07h,'$'
;
;---------------------------------------------------------------------------
;
;    tsk_emergency_exit is entered by DOS when a task group exits
;    without releasing the current group.
;    Registers are set up, remove_group is called, and the program
;    is terminated by jumping to the terminate_address.
;
tsk_emergency_exit    proc    far
;
    pushf
    sub    sp,4        ; make room for return addr
    push    bp
    mov    bp,sp
    push    ax
    push    bx
    push    cx
    push    dx
    push    si
    push    di
    push    ds
    push    es
    mov    ax,@CTASK_DATA
    mov    ds,ax
;
    les    bx,tsk_glob_rec.current_task[bx]
    les    bx,es:tgroup[bx]
    mov    ax,word ptr es:grp_exit_addr[bx]
    mov    2[bp],ax
    mov    ax,word ptr es:grp_exit_addr+2[bx]
    mov    4[bp],ax
;
    callp    tsk_remove_group,<<es,bx>,0>
;
    mov    dx,offset group_term_msg
        cmp    ax,0
    je    emergency_end
    jb    pg_fatal
;
    les    bx,tsk_glob_rec.current_task[bx]
    les    bx,es:tgroup[bx]
    callp    tsk_kill_group,<<es,bx>>
    call    tsk_remove_tasker
;
    mov    dx,offset term_err_msg
;
emergency_end:
;
    mov    ax,cs
    mov    ds,ax
    mov    ah,9
    int    21h
;
    pop    es
    pop    ds
    pop    di
    pop    si
    pop    dx
    pop    cx
    pop    bx
    pop    ax
    pop    bp
    iret
;
pg_fatal:
    mov    si,offset gcb_mixup_err
    jmp    short fatal_error
;
tsk_emergency_exit    endp
;
;--------------------------------------------------------------------------
;
;    fatal_error can be called if the system can't continue for
;    some reason. It issues an error message and halts the system.
;    SI must point to the '$'-terminated error message.
;
;    tsk_fatal does the same, but assumes C calling sequence and
;    a zero-terminated string.
;
Globalfunc tsk_fatal,<strp: far ptr>
;
    cld
    lds    si,strp
    jmp    short dis_err
;
tsk_fatal    endp
;
fatal_error:
    mov    ax,cs
    mov    ds,ax
;
dis_err:
    IF    IBM
    xor    ax,ax
    int    10h        ; re-init display
fatal_loop:
    lodsb
    cmp    al,'$'
    je    fatal_end
    or    al,al
    jz    fatal_end
        mov     bx,7
        mov     ah,14
    int    10h
    jmp    fatal_loop
    ELSE
    mov    dx,si
    mov    ah,9
    int    21h
    ENDIF
fatal_end:
    sti
    jmp    fatal_end
;
;--------------------------------------------------------------------------
;
;    void CGlobalfunc tsk_fatal_pmd (byteptr string, ...)
;
;    tsk_fatal_pmd is only present in "checking" mode.
;    It does a minimal "post mortem dump", and displays the
;    error message passed as parameter.
;    The messages are output to both the primary and secondary
;    monitor via the "regen" printf routines in tskprf.
;    The system is then halted, this routine never returns.
;
    IF    CHECKING
;
;
CGlobalfunc    tsk_fatal_pmd,<txt: far ptr,argp:far ptr>
;
;    int    3    ; uncomment to break to debugger
    push    sp
    push    ss
    push    es
    push    ds
    push    di
    push    si
    push    dx
    push    cx
    push    bx
    push    ax
;
    mov    ds,tsk_dgroup
    callp    preempt_off
    callp    tsk_set_currdis
;
    callp    tsk_rputc,<0ch>
    les    di,txt
    lea    bx,argp
    call    @fatal_dump
;
    callp    tsk_set_dualdis
    or    ax,ax
    jz    no_second
;
    callp    tsk_rputc,<0ch>
    les    di,txt
    lea    bx,argp
    call    @fatal_dump
;
no_second:
    jmp    fatal_end
;
tsk_fatal_pmd    endp
;
;
pmd1    db    0ah
    db    'AX = %04X  BX = %04X  CX = %04X  DX = %04X',0ah
    db    'SI = %04X  DI = %04X  DS = %04X  ES = %04X',0ah
    db    'SS = %04X  SP = %04X  BP = %04X',0ah
    db    'IP = %04X  CS = %04X',0ah,0
pmd2    db    'Current Task = %FP'
    IF    TSK_NAMED
    db    ' (%s)'
    ENDIF
    db    0ah,0
pmde    db    'System Halted',0
;
;
@fatal_dump    proc    near
;
    callp    tsk_vrprintf,<<es,di>,<ss,bx>>
    mov    bx,sp
    add    bx,2
    callp    tsk_vrprintf,<<cs,#pmd1>,<ss,bx>>
;
    IF    SINGLE_DATA
    mov    bx,offset tsk_glob_rec
    push    ds
    pop    es
    ELSE
    les    bx,tsk_global
    ENDIF
    les    bx,es:current_task[bx]
    IF    TSK_NAMED
    lea    dx,tname.nname[bx]
    callp    tsk_rprintf,<<cs,#pmd2>,<es,bx>,<es,dx>>
    ELSE
    callp    tsk_rprintf,<<cs,#pmd2>,<es,bx>>
    ENDIF
    callp    tsk_rprintf,<<cs,#pmde>>
    ret
;
@fatal_dump    endp
;
    ENDIF
;
;---------------------------------------------------------------
;
    .tsk_ecode
;
    ENDIF
;
        end