From mboxrd@z Thu Jan 1 00:00:00 1970 From: Leon Woestenberg Subject: Re: rt application question with rs232 communication Date: Sun, 15 Mar 2009 03:07:13 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: rt-users To: Cliff Brake Return-path: Received: from mail-ew0-f177.google.com ([209.85.219.177]:41849 "EHLO mail-ew0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751635AbZCOCHQ convert rfc822-to-8bit (ORCPT ); Sat, 14 Mar 2009 22:07:16 -0400 Received: by ewy25 with SMTP id 25so3040756ewy.37 for ; Sat, 14 Mar 2009 19:07:13 -0700 (PDT) In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: Hello Cliff, On Tue, Mar 10, 2009 at 1:44 PM, Cliff Brake wr= ote: > Clarification, I don't have the RT patch applied, just CONFIG_PREEMPT > from Linus's kernel. =A0Reviewing my notes from several years ago, I = ran > into a similar issue and the RT patch fixed it, so now to figure out > the best way to get a recent RT patched ARM kernel ... > >> timing. =A0However, it seems that the system has trouble receiving t= he >> response in a timely fashion. =A0I often observe that it takes at le= ast >> 10ms for the application to receive the response data after the data >> has appeared on the rs232 bus. =A0Is the RT patch something that wou= ld We are running a real-time RS-485 protocol where the time window is 1 ms and only under heavy load we got deadline misses > 1 ms. Unfortunately I didn't measure the max latency then, but 10 ms sounds like excessive latency to me. Under 2.6.24.7-rt24 (or whatever -rtxy in that series) we have never missed the 1 ms deadline. That's on XScale IXP4xx @533 MHz, Regards, --=20 Leon -- To unsubscribe from this list: send the line "unsubscribe linux-rt-user= s" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html