Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

                                                     ◄Up► ◄Next► ◄Previous►
────────────────────────────────────────────────────────────────────────────
 
mov     ax, 1680h   ; Release Current VM Time-Slice
int     2Fh         ; multiplex interrupt
 
Release Current VM Time-Slice (Interrupt 2Fh Function 1680h) directs Windows
to suspend the time slice of the current VM and start a new time slice for
another VM. MS-DOS programs use this function when they are idle, such as
when waiting for user input, to allow 386 enhanced-mode Windows to run other
programs that are not idle.
 
Return Value
 
The return value is 00h in the AL register if the function is supported.
Otherwise, AL is unchanged (contains 80h).
 
Comments
 
Only non-Windows programs should use Release Current VM Time-Slice; Windows
applications should yield by calling the WaitMessage function. A program can
call this function at any time, even when running in environments other than
386 enhanced-mode Windows environment. If the current environment does not
support the function, the function returns and the program continues
execution.
 
Windows suspends the current VM only if there is another VM scheduled to
run. If no other VM is ready, the function returns to the program and
execution continues. A program should call the function frequently (for
example, once during each pass of the program's idle loop) to give Windows
ample opportunity to check for other VMs that are ready for execution.
 
Before calling this function, a program should check that the Interrupt 2Fh
address is not zero.
 
Example
 
The following example checks for for a valid Interrupt 2Fh address, then
releases the current VM time slice:
 
    mov     ax, 352Fh       ; Get Interrupt Vector
    int     21h
 
    mov     ax, es
    or      ax, bx
    jz      Skip_Idle_Call  ; es:bx is equal to 0:0
 
    mov     ax, 1680h       ; otherwise, Release Current VM Time-Slice
    int     2Fh
Skip_Idle_Call:
 
 
                                      ♦