🚀 go-pugleaf

There is a flag buried in the internal data area for MS-DOS called INDOS.
A 0 value indicates that MS-DOS is not currently executing in a critical
section. Any other value indicates that you can not make a Int 21 call.

To find out the current value of this flag:

	1. Before interrupt processing starts execute the GET_INDOS_FLAG
	   function. This is function 34h in MS-DOS.
	   (i.e. AX = 34h when doing the Int 21)

	2. Upon return you don't get the flag but rather a pointer to
	   it in ES:BX.  ES = the segment address and BX = the offset
	   address of the INDOS flag.

	3. When the interrupt occurs directly test this byte from the
	   interrupt handler to determine if calls to MS-DOS are
	   allowable. You will have to determine appropriate actions
	   if the interrupt occurred during a critical section of MS-DOS.

Hope this helps.

Jim Vallino
{allegra,ihnp4}!princeton!siemens!jrv