Date:	Tue, 28 Feb 1995 19:09:12 +0500
From:	hvb AT netrix DOT com
To:	djgpp AT sun DOT soe DOT clarkson DOT edu
Subject:	How to avoid nested interrupts?

We try to reprogram the clock to interrupt once per milli second.

The protected mode interrupt issues a call to the original real mode
interrupt function (via go32_dpmi_simulate_fcall_iret) once every
18.2msec to keep the DOS clock happy.

The clock call back interrupt will call the protected mode function to
keep the counter arithmetic in sync (using
go32_dpmi_allocate_real_mode_callback_iret and
go32_dpmi_set_real_mode_interrupt_vector).

The problem we get is sometimes while accessing the disk on a 386
system, the protected mode to real mode switching is so slow that when
the real mode interrupt returns to the protected mode, another
interrupt can occur immediately.  In fact, there are so many of the
stacked up that it overflowed the stack.

The question is: how do I set up so that when real mode returns
to protected mode the processor remains interrupt disabled?  I have
issued an "cli" in the protected mode prior to call
go32_dpmi_simulate_fcall_iret.

It seems that the INTERRUPT flag which is cleared in protected mode,
is set on return from go32_dpmi_simulate_fcall_iret.

Thanks in advance.

==============================================================
Hung Bui                            Internet: h DOT bui AT ieee DOT org
Netrix Corporation                    Phone: +1 703 793 1016
13595 Dulles Technology Drive           Fax: +1 703 713 3805
Herndon Va 22071
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