From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262863AbUB0NYh (ORCPT ); Fri, 27 Feb 2004 08:24:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262860AbUB0NYh (ORCPT ); Fri, 27 Feb 2004 08:24:37 -0500 Received: from nsmtp.pacific.net.th ([203.121.130.117]:59319 "EHLO nsmtp.pacific.net.th") by vger.kernel.org with ESMTP id S262843AbUB0NYe (ORCPT ); Fri, 27 Feb 2004 08:24:34 -0500 Date: Fri, 27 Feb 2004 21:24:25 +0800 From: "Michael Frank" To: "Etienne Lorrain" , linux-kernel@vger.kernel.org Subject: Re: Why no interrupt priorities? References: <20040227113725.12307.qmail@web11808.mail.yahoo.com> Content-Type: text/plain; charset=US-ASCII; format=flowed delsp=yes MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Message-ID: In-Reply-To: <20040227113725.12307.qmail@web11808.mail.yahoo.com> User-Agent: Opera M2/7.50 (Linux, build 600) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 27 Feb 2004 12:37:25 +0100 (CET), Etienne Lorrain wrote: > Russell King wrote: >> Michael Frank wrote: >> > Is this to imply that edge triggered shared interrupts >> > are used anywhere? >> >> It is (or used to be) rather common with serial ports. Remember that >> COM1 and COM3 were both defined to use IRQ4 and COM2 and COM4 to use >> IRQ3. > > Some unusual hardware could handle two ports on the same IRQ (the > same card mixing itself the IRQ of the two COM port present on the > same ISA card) but the mixing could not be reliably handled at the > ISA level. Using a resistor and/or a diode instead of a jumper to > select the IRQ could also do the trick. So the software was ready > to handle two interrupts from two UART on the same IRQ - but you > had to have special hardware. I used those cheapy 8 Channel 8250 serial cards and modified them by oring 8 interrupts to irq 3. The IRQ was set to level triggered and on an IRQ one polled the status regs of all 8 channels. That was _just_ OK on a 8MHz 286 at 9600 baud in a custom designed low latency application (no FIFOS here). > > Some people had success having a modem on COM1 and a serial _mouse_ > on COM3 (or the other way around) because the COM1/modem was winning > the control of the ISA IRQ and the COM3/modem was loosing but because > of 1200 bauds transmission speed the timer interrupt was recovering the > char received. So they could not tell the difference and did not know > why inverting the two serial plug did not work. :-( Regards Michael