From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 4 Sep 2001 14:24:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 4 Sep 2001 14:24:01 -0400 Received: from maild.telia.com ([194.22.190.101]:2794 "EHLO maild.telia.com") by vger.kernel.org with ESMTP id ; Tue, 4 Sep 2001 14:23:49 -0400 Message-Id: <200109041823.f84INqE13918@maild.telia.com> Content-Type: text/plain; charset="iso-8859-1" From: Roger Larsson To: "Christopher Friesen" , Fred Subject: Re: Should I use Linux to develop driver for specialized ISA card? Date: Tue, 4 Sep 2001 20:19:17 +0200 X-Mailer: KMail [version 1.3] Cc: linux-kernel@vger.kernel.org In-Reply-To: <01090410264000.14864@bits.linuxball> <3B950034.17909E5D@nortelnetworks.com> In-Reply-To: <3B950034.17909E5D@nortelnetworks.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday den 4 September 2001 18:24, Christopher Friesen wrote: > Fred wrote: > > I'm curious, Alan, Why? I'm a hardware developer, and I would have > > assumed that linux would have been ideal for real time / embedded > > projects? (routers / controllers / etc.) Is there, for instance, a reason > > to suspect that linux would not be able to respond to interrupts at say > > 8Khz? > > of course I know nothing of rtlinux so I'll read. > > I'm involved in a project where we are using linux in an embedded > application. We've got a gig of ram, no hard drives, no video, and the only > I/O is serial, ethernet and fiberchannel. > > We have a realtime process that tries to run every 50ms. We're seeing > actual worst-case scheduling latencies upwards of 300-400ms. > > So while interrupts can be handled pretty quickly, you'll want to make sure > that your buffers are big enough that your userspace app only needs to run > every half second or so. > > You may be better off with rtlinux if you need better response. (Or if > you're on x86 hardware you could look at the low-latency patches.) 1) Why shouldn't the low-latency patches work for another architecture? Andrew Morton might be interested to fix other architectures too. (but most patches are not in architecture specific code) 2) Montavistas reschedulable kernel is a very interesting approach, newly released an update by Robert Love http://kpreempt.sourceforge.net/ http://tech9.net/rml/linux/patch-rml-2.4.10-pre2-preempt-kernel-1 (there are still some spikes, but the floor is smooth) But note you with both approaches you want to run the latency critical process with a higher priority, and probably with the memory locked down. See example code (latencytest) at: http://www.gardena.net/benno/linux/audio/ (but there is no need to run at the maximum possible priority since your process will be alone anyway...) /RogerL -- Roger Larsson Skellefteċ Sweden