The program is a BBS program and need to continually poll the
serial line. OK, I know polling isn't great, but I interface to
the FOSSIL driver and have no interrupt handling routines.

I know that there are DesqView Interrupts which allow the program
to release unused process time. Surely, such a thing must exist in Warp
as well?

Any hints on this would be greatly apreciated.

I think that most multitaskers hook INT28 (description follows).
Therefore, you should try to call it after each polling of the serial
line, you can do a

  inline($CD,$28)

to invoke this interrupt. Therefore, you do not have to detect OS/2 for
it to work.  

I should point out that I used it in one of my programs, but that I
cannot swear that it does something since I work on a 286 :-( Try it and
tell me if it works.

Hope this helps.

Jean-Marc.

From Ralf Brown's interrupt list:

INT 28 C - DOS 2+ - DOS IDLE INTERRUPT
        SS:SP = top of MS-DOS stack for I/O functions
Return: all registers preserved
Desc:   This interrupt is invoked each time one of the DOS character input
          functions loops while waiting for input.  Since a DOS call is in
          progress even though DOS is actually idle during such input waits,
          hooking this function is necessary to allow a TSR to perform DOS
          calls while the foreground program is waiting for user input.  The
          INT 28h handler may invoke any INT 21h function except functions
          00h through 0Ch.
Notes:  under DOS 2.x, the critical error flag (the byte immediately after the
          InDOS flag) must be set in order to call DOS functions 50h/51h from
          the INT 28h handler without destroying the DOS stacks.
        calls to INT 21/AH=3Fh,40h from within an INT 28 handler may not use a
          handle which refers to CON
        at the time of the call, the InDOS flag (see INT 21/AH=34h) is normally
          set to 01h; if larger, DOS is truly busy and should not be reentered
        the default handler is an IRET instruction
        supported in OS/2 compatibility box
        the _MS-DOS_Programmer's_Reference_ for DOS 5.0 incorrectly documents
          this interrupt as superseded
SeeAlso: INT 21/AH=34h,INT 2A/AH=84h,INT 2F/AX=1680h

var register:registers;
procedure idle;
begin
register.ah := 134;
register.cx := 0;
register.dx := 1000;
intr (21,register);
end;

: The program is a BBS program and need to continually poll the
: serial line. OK, I know polling isn't great, but I interface to
: the FOSSIL driver and have no interrupt handling routines.

Let me tell you about my experiences with serial communication in the
DOS box of OS/2. First thing: when the box is idle it will show with
most monitoring programs a CPU-load of 100%. The moment you start some-
thing, this drops. No harm in that, it is caused by some DOS needed
polling, but because this happens with low-priority it doesn't give a
performance hit.

Second is RS232 access. I used self-made interrupt driven routines
(see ftp://garbo.uwasa.fi/pc/turbopas/comtty30.zip or
     ftp://oak.oakland.edu/pub/turbopas/comtty30.zip) but discovered
that when you implement for example a terminal emulator with a loop
that constantly checks both keyboard and serial port, performance
improves drastically by putting somewhere in the loop a very short
call to "Delay()". Probably this call enables the process scheduler
to take over.

Willem

In <3s9260$...@mars.darmstadt.gmd.de>, Daniel Tietze

   I had a similar problem running a compiled BASIC program under OS/2.  It
should be very simple to port to Pascal.  I assembled a zip file
(qbslice.zip) and posted it to ftp-os2.nmsu.edu in /dos.

   Here are the relevant BASIC routines:

FUNCTION DOSVersion! STATIC

' This routine determines the OS version that the program is runing under.
' Needed, e.g., in case we are running graphics in a window in OS/2 (many
' graphics modes aren't virtualized in a window if runing WPS in high
' resolution)

DIM reg AS RegType
reg.ax = &H3000
Interrupt &H21, reg, reg
major% = reg.ax MOD 256    
minor% = reg.ax \ 256      
DOSVersion! = major% + minor% / 100   ' 20.3 for OS/2 Warp version 3
END FUNCTION

SUB SliceMe

' This subroutine gives up a time slice to Warp.
' It is documented in IBM's OS/2 Virtual Device Driver manual, part
' of the OS/2 Technical Library, and in Ralf Brown's Interrupt List.

DIM reg AS RegType
reg.ax = &H1680
Interrupt &H2F, reg, reg ' Give up the time slice to OS/2
END SUB

   More information is available in the .zip file.