From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261681AbVEDVpm (ORCPT ); Wed, 4 May 2005 17:45:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261690AbVEDVpl (ORCPT ); Wed, 4 May 2005 17:45:41 -0400 Received: from [81.2.110.250] ([81.2.110.250]:50830 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S261688AbVEDVpN (ORCPT ); Wed, 4 May 2005 17:45:13 -0400 Subject: Re: tricky challenge for getting round level-driven interrupt problem: help! From: Alan Cox To: Luke Kenneth Casson Leighton Cc: Linux Kernel Mailing List , Linux ARM Kernel list In-Reply-To: <20050504205831.GF8537@lkcl.net> References: <20050503215634.GH8079@lkcl.net> <1115171395.14869.147.camel@localhost.localdomain> <20050504205831.GF8537@lkcl.net> Content-Type: text/plain Content-Transfer-Encoding: 7bit Message-Id: <1115243014.19844.62.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 (1.4.6-2) Date: Wed, 04 May 2005 22:43:35 +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mer, 2005-05-04 at 21:58, Luke Kenneth Casson Leighton wrote: > i believe i get it: you raise a level-triggered interrupt which _stays_ > raised until such time as your fifo is empty. Bingo. It only goes away when the chip really has nothing left to say. > all - that sometimes (frequently, in fact - about 1 in every > 50 times) it hasn't got round to clearing the level-driven > interrupt by the time we come out of the ARM ISR (!) So you'll poll again and find there is no pending work to do. > hence the redesign to do alternate read-write-read-write, and making > reads exclusive of writes, etc. and maybe even turn the IRQ off and use a timer if its slow and not sensitive to latency.. ? > ... so - in your opinion, alan, is the old approach we had > actually _on_ the right lines? level triggered IRQ does sort of expect the other end responds promptly to be efficient as opposed to merely reliable. > also, are you going to ukuug in august, it being _in_ > aberystwyth and all :) Its not in Aberystwyth, but I might be. Its in Swansea 8)