Path: utzoo!attcan!uunet!mcvax!hp4nl!botter!star.cs.vu.nl!ast
From: ast@cs.vu.nl (Andy Tanenbaum)
Newsgroups: comp.os.minix
Subject: Re: Help! Minix 1.3 & PS/2 Model 80
Message-ID: <1975@ast.cs.vu.nl>
Date: 26 Jan 89 13:50:27 GMT
References: <1023@uvm-gen.UUCP> <1906@ast.cs.vu.nl> <1259@ditsyda.oz> <1941@ast.cs.vu.nl> <1480@ditsyda.oz>
Reply-To: ast@cs.vu.nl (Andy Tanenbaum)
Organization: VU Informatica, Amsterdam
Lines: 17

In article <1480@ditsyda.oz> evans@ditsyda.oz (Bruce Evans) writes:
>Interrupt() must be kept short since it runs with interrupts disabled. So I
>don't want to have any port_out()s in it (a dozen or so instructions in C
>compared with 2 in assembler) or lots of cases to check. Attention to this
>detail was one of the things required to boost rs232 performance from 300
>baud to 19200 baud on a 5MHz 8088.

Good point.  Perhaps it is indeed best to move all the EOI stuff to the
tasks instead of the interrupt handlers, since the tasks an run with
interrupts enabled.

This still leaves us with the question of how to exit from the interrupt
handler and not get another interrupt instantly.  Whatever solution is
chosen should be efficient.  Doing a port_out to the 8259 to change the
mask is as expensive as doing a port_out to the 8259 for EOI.

Andy Tanenbaum (ast@cs.vu.nl)