Date: Sun, 9 Apr 2000 08:47:25 +0200 (IST) From: Eli Zaretskii X-Sender: eliz AT is To: Willem Bekker cc: djgpp AT delorie DOT com Subject: Re: HARDWARE INTERRUPT HANDLING BY CWSDPMI In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Reply-To: djgpp AT delorie DOT com Errors-To: nobody AT delorie DOT com X-Mailing-List: djgpp AT delorie DOT com X-Unsubscribes-To: listserv AT delorie DOT com Precedence: bulk On Tue, 4 Apr 2000, Willem Bekker wrote: > I have a small question. How much does the handling of real mode interrupt > handlers slow down when a djgpp program using cwsdpmi is running. If, for > example, I have a standard tsr handling com port interrupts at a high rate > with real mode code, would a program like lynx under dos cause the system to > loose interrupts, while a real mod program would not. A DJGPP program indeed incurs additional overhead, because under DPMI, all hardware interrupts are reflected to protected-mode handlers first, and only if unhandled, they are passed to real-mode handlers. The mode switch that this involes takes up hundreds of CPU cycles. Whether this overhead will cause you to lose interrupts, I don't know. In general, I won't expect the overhead to be severe enough, so the system might as well cope with the additional load. > Another question is how stable would a system be with a tsr requiring > cwsdpmi. For example would a system with such a tsr survive the starting up > and the shutting down of Windows. You cannot start Windows when a DJGPP program is running, because the CPU is already in protected mode. Windows will refuse to start.