HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens

                 INT 21,34 - Get Address to DOS Critical Flag
                        INDOS  (Undocumented DOS 2.0+)

       AH = 34h

       on return:
       ES:BX = address of a byte indicating whether a DOS call is
               in progress.  No DOS calls should be made if set.

       - AKA the INDOS flag, this critical section flag may be checked from
         within an interrupt handler before requesting a DOS service. It is
         a semaphore that is non-zero when DOS is busy, and zero otherwise.
       - though this flag indicates whether a DOS interrupt is active, it
         should not be used alone to determine DOS is safe for re-entry;
         Here's the standard rule for safe DOS entry: if INT 28 is active
         or this flag and the critical error flag are clear then it is safe
         to call DOS
       - this interrupt should be used only during TSR initialization;
         the returned pointer should be used thereafter
       - this flag is cleared after a critical error (INT 24)
       - ES:BX-1 points to the critical error flag for DOS 3.x+
         ES:BX+1 points to the critical error flag for DOS 2.x
         ES:BX-1AA points to the critical error flag for COMPAQ DOS 3.0
         INT 21,5D in DOS 3.x+ can be used to locate the critical
         error flag

Esc or Alt-X to exit int 21,34 Home/PgUp/PgDn/End ←↑↓→
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