[Q]: Generic time slicing function for many multi-taskers

[A]: Serg Projzogin

;========================================================================
;
; SLICE.ASM
;
; Provides a generic time slicing function for all multi-taskers I know
; or care about.
;
; Note that this library is Turbo Assembler specific, since I have long
; since weaned myself from MASM's brain-dead memory addressing syntax.
;
; This library is designed to be easily extended; for each new
; multi-tasker supported, you need to write a detect routine and a
; time-slice routine.
;
; Your detection function will take no input, and should return with
; carry set if the associated multi-tasker is detected. This routine
; may safely alter register AX. No other registers should be altered.
;
; The time-slice routine will take no input and give up a "standard"
; timeslice for the associated multi-tasker. This routine may safely
; alter registers AX, BX and DS. No other registers should be altered.
;
; Once you have such routines written, add their addresses to the
; arrays detect_func and slice_func below. Increment the
; NumMultitaskers equate, and you're done.
;
; This library placed in the public domain by Kevin Vigor, 1/5/93.
; I would, however, appreciate it if you do the following two things:
;
; 1: If you distribute an altered version of this source, please add to
; this header a log of your changes;
;
; 2: If you discover any bugs or extend this library, please send a copy
; of your changes to me at one of the below addresses:
;
; Compuserve: 72500,3705
; Internet: kevin@wicat.com
; 72500.3705@compuserve.com ;========================================================================


IDEAL ; Requires Turbo Assembler.

MODEL SMALL ; This may be changed to any model safely. Note,
; however, that you will not be able to link
; this routine to a .COM, since it makes explicit
; segment refrences. This is just laziness; I
; haven't bothered to do all the ifdef'ing.

LOCALS ; Allow local symbols starting with @@

DATASEG

; Define known multitaskers.
None equ 0
DesqView equ 1
Windows_3x equ 2
OS2_2x equ 3

NumMultitaskers EQU 3 ; Do not include 'None'

current_tasker dw 0 ; Detected multi-tasker

; Table of detection routines.

detect_func DW OFFSET @code:dummy_detect
DW OFFSET @code:Desqview_detect
DW OFFSET @code:Windows_3X_detect
DW OFFSET @code:OS2_2x_detect

; Table of time-slicing functions.

slice_func DW OFFSET @code:dummy_slice
DW OFFSET @code:Desqview_slice
DW OFFSET @code:Win_3x_or_OS2_2x_slice
DW OFFSET @code:Win_3x_or_OS2_2x_slice

CODESEG

PUBLIC _detect_multitasker, _timeslice

;; Detection routines: return with carry set if the appropiate tasker is
;; detected and clear if not.

PROC dummy_detect ; SHould never be called, but does no harm.
clc ; Always fail.
ret
ENDP

PROC Desqview_detect ; Return with carry set if Desqview detected.
;
; This routine is based on information in the Desqview version 2.x manual.
push ax
push bx
push cx
push dx

mov cx, 'DE'
mov dx, 'SQ'
mov ax, 02B01h ; DOS set date function.
int 021h
cmp al, 0FFh ; Did DOS report the invalid date?
jnz @@desqview ; If not, we've got Desqview.

clc ; Report failure.

@@clean_stack:
pop dx
pop cx
pop bx
pop ax
ret

@@desqview:

; BH = Desqview major version, BL = Desqview minor version. I have no idea
; at what version the timeslicing calls became available, so I just assume
; they are supported. If this is an invalid assumption, this would be the
; place to test.

stc ; Report sucess.
jmp short @@clean_stack ; and exit.

ENDP ; Desqview_detect.

PROC Windows_3X_detect
; Note: this function detects Windows 3.x in enhanced mode only.
; I am not a Windows guru (or even user), but I believe there is no
; capability for time-slicing in standard or real modes, therefore this
; function is sufficient for the purposes of this library.
; I am basing this function on the fine book PC Interrupts, which lists
; a number of magic values which mean WIndows 3.x enhanced mode is not running.

push ax

mov ax, 01600h
int 02Fh

cmp al, 00h
jz @@no_Windows

cmp al, 080h
jz @@no_Windows

cmp al, 01h ; Windows/386 2.x; not supported.
jz @@no_windows

cmp al, 0FFh ; Windows/386 2.x; not supported.

; If AL is none of the above values, it is the Windows major version number.

cmp al, 03h ; At least Win 3.0?
jb @@no_windows

stc ; Yes, report sucess.
pop ax
ret

@@no_windows:
clc ; Report failure.
pop ax
ret
ENDP

PROC OS2_2x_detect
; I do not know of an 'official' way of testing for OS/2 presence; the
; method used here is to test the DOS version. If the major version
; is 20 or above, we assume we're in an OS/2 2.x DOS box.

push ax
push cx

mov ah, 030h ; DOS get version fn.
int 021h

cmp al, 014h ; 20 decimal.
jb @@no_OS2

stc ; Report sucess.

@@clean_stack:
pop cx
pop ax
ret

@@no_OS2:
clc ; Report failure.
jmp short @@clean_stack

ENDP

;; Time slicing routines for each tasker.

PROC dummy_slice ; Should never be called, but does no harm. ret
ENDP

PROC Desqview_slice ; Give up a slice under Desqview.

ASSUME cs:@code, ds:nothing, es:nothing
mov ax, 0101Ah ; Switch to DV's stack.
int 015h
mov ax, 01000h ; Give up time-slice.
int 015h
mov ax, 01025h ; Restore local stack.
int 015h
ret
ENDP

PROC Win_3x_or_OS2_2x_slice

; This call works under either Windows 3.x in Enhanced mode, or OS/2 2.x

ASSUME ds:@code, ds:nothing, es:nothing
mov ax, 01680h ; Win 3.x / OS/2 2.x timeslice call. int 02Fh
ret
ENDP


PROC _detect_multitasker
; Tries to find a multi-tasker.
; Returns the ID in AX, and sets up the internal data to call _timeslice.
;
; Note that this function can be safely called from Turbo/Borland C. I have
; no idea about other compilers.

push ds
push bx
push cx

ASSUME cs:@code, ds:nothing, es:nothing
mov ax, @data
mov ds, ax
ASSUME ds:@data

mov cx, NumMultitaskers ; Number of routines to try.
xor ax, ax

@@detect_loop:
inc ax

; AX holds the number of the detection routine to try.
push ax
shl ax, 1
mov bx, ax ; BX = AX * 2

call [detect_func + bx] ; Call this function.
pop ax ; Restore AX.
jc @@found_one ; quit now if we hit one.

loop @@detect_loop ; Go through all known detection routines.

xor ax, ax ; Signal failure.
jmp short @@clean_stack ; and exit.

@@found_one:
mov [current_tasker], ax

@@clean_stack:
pop cx
pop bx
pop ds

ASSUME ds:nothing

ret
ENDP

PROC _timeslice
; Give up a timeslice. Depends on having the current_tasker global set by
; a call to detect_multitasker. However, will call dummy_slice and do no
; harm if detect_multitasker has not been called.
;
; Note that this function can be safely called from Turbo/Borland C. I have
; no idea about other compilers.

push ds
push ax
push bx

ASSUME cs:@code, ds:nothing, es:nothing
mov ax, @data
mov ds, ax
ASSUME ds:@data

mov ax, [current_tasker]
shl ax, 1 ; BX = AX * 2
mov bx, ax

call [slice_func + bx] ; Call appropiate time-slice function.

pop bx
pop ax
pop ds
ret
ENDP

END
=== Cut ===

=== Cut ===
/* SLICE.H
*
* Turbo/Borland C prototypes for the functions provided by SLICE.ASM
*
*/
#ifndef SLICE_H_
#define SLICE_H_

/* Returns zero if no known multi-tasker found, or an ID if one is. */
int detect_multitasker(void);

/* Give up a timeslice. detect_multitasker should be called first. */
void timeslice(void);

#endif
=== Cut ===

=== Cut ===
/*
* TEST.C
*
* Stupid test-bed for the time-slicing functions in SLICE.ASM;
* simply detects a multi-tasker and then waits for a keystroke
* twice, once with time-slicing and once without.
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h>


#include "slice.h"

static char *tasker_names[] =
{
"None",
"DesqView",
"Windows 3.x (enhanced)",
"OS/2 2.x"
};

void main(void)
{
int tasker = detect_multitasker();

printf("Multitasker found: %s\r\n", tasker_names[tasker]);

if (!tasker)
exit(1);

puts("Waiting for keystroke (no slicing...)");
while (!kbhit())
;

getch();

puts("Waiting for keystroke (slicing...)");
while (!kbhit())
timeslice();

getch();

exit(0);
}

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