From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Howard Subject: Re: serial flow control appears broken Date: Thu, 26 Jul 2007 09:28:06 -0700 Message-ID: <46A8CB96.1010501@howardsilvan.com> References: <46A7FE6A.4030309@howardsilvan.com> <20070726123420.GA14163@informatik.uni-freiburg.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from gateway.howardsilvan.com ([64.146.212.27]:33647 "EHLO mail.howardsilvan.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760998AbXGZQ31 (ORCPT ); Thu, 26 Jul 2007 12:29:27 -0400 In-Reply-To: <20070726123420.GA14163@informatik.uni-freiburg.de> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: =?ISO-8859-1?Q?Uwe_Kleine-K=F6nig?= Cc: linux-serial@vger.kernel.org, tytso@mit.edu, rmk@arm.linux.org.uk, linux-kernel@vger.kernel.org Uwe Kleine-K=F6nig wrote: >Hello, > > =20 > >>This is evidenced in hardware flow control by a little LED labeled "R= TS"=20 >>that is on the external modem. This LED lights up when pin 7 of the = DB9=20 >>serial connection is given +12Vdc current (signalling "RTS" is on - t= hat=20 >>the host can accept data). The LED goes dark when the current is=20 >>removed (signalling that the host cannot accept data). This "RTS" LE= D=20 >>never flickers at all, as it should, when receiving these bursts of d= ata=20 >>- the LED stays lit as long as the serial cable is connected to the=20 >>host... and yet I will see those "input overrun" messages. Thus, it=20 >>seems quite clear that the Linux serial tty driver is not deasserting= =20 >>RTS as it should in hardware flow control. (And probably the analogo= us=20 >>problem exists in software flow control, too.) >> =20 >> >I don't know the relevant timings for problem, but just to be sure tha= t >your prerequisites are correct: How did you check that the LED stays >lit all the time? Just from looking might not be accurate. You might >want to mesure the signal with an oscilloscope. > The manufacturer is using a scope to look for RTS and they're not seein= g=20 it, either. I just use my eyes to look at the LED, but I can see the=20 CTS, DTR, DCD, RD, and TD lights blink, flicker, or dim... (and TD, RD,= =20 and CTS tend to go on and off rather quickly). All of that said... even though I don't see RTS flicker or blink or dim= =20 when using kernel 2.2.5 (RedHat 6.0) I don't have any problems using=20 115200 bps DTE-DCE communication rate. Thanks, Lee. - To unsubscribe from this list: send the line "unsubscribe linux-serial"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html