🚀 go-pugleaf

Hi.  There are plenty of mostly undocumented INT 21h calls that can be used to
determine if it's safe to make a DOS call from within an interrupt handler, but
there are also two function calls that can be used to get the address of the
Swappable Data Area (SDA) so that if a DOS call is being processed all you do is
swap out the SDA into your own buffer, make all the DOS calls you want, and
swap the saved data back into the SDA!  I can't remember the specifics since I
don't have any docs with me, but I know it's INT 21h function 5D06h for DOS 3.x
and function 5D0Bh for DOS 4.x and later.  However, you still have to pay
attention to "critical sections" delimited by calls to certain (sub)functions
of INT 2Ah.  The book <Undocumented DOS> by Ralf Brown, Andrew Schulman, and
others explains all about this.

Tschuess,
David Paschal