From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261559AbUB0Lh2 (ORCPT ); Fri, 27 Feb 2004 06:37:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261703AbUB0Lh2 (ORCPT ); Fri, 27 Feb 2004 06:37:28 -0500 Received: from web11808.mail.yahoo.com ([216.136.172.162]:1941 "HELO web11808.mail.yahoo.com") by vger.kernel.org with SMTP id S261686AbUB0Lh0 (ORCPT ); Fri, 27 Feb 2004 06:37:26 -0500 Message-ID: <20040227113725.12307.qmail@web11808.mail.yahoo.com> Date: Fri, 27 Feb 2004 12:37:25 +0100 (CET) From: =?iso-8859-1?q?Etienne=20Lorrain?= Subject: Re: Why no interrupt priorities? To: linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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. If you are talking of old ISA serial cards, the IRQ were "shared" in the sense that the IRQ pin was not connected to the microprocessor when the device was not open (under Linux). So you could reliably have COM1 and COM3 on IRQ4 if you did not use the two devices at the same time - or use one of them in the polling mode (IRQ 0: handle by the timer at low speed). 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. 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. Now if you are talking of newer motherboard with COM port integrated, you may have been able to share (but unusual) - if you are talking of PCI card serial ports then that is another story. Etienne. Yahoo! Mail : votre e-mail personnel et gratuit qui vous suit partout ! Créez votre Yahoo! Mail sur http://fr.benefits.yahoo.com/ Dialoguez en direct avec vos amis grâce à Yahoo! Messenger !Téléchargez Yahoo! Messenger sur http://fr.messenger.yahoo.com