Online 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
[helppc.bosbyte.nl] INDOS