From owner-freebsd-stable@FreeBSD.ORG Tue Jan 12 16:32:22 2010 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 4919B106566B for ; Tue, 12 Jan 2010 16:32:22 +0000 (UTC) (envelope-from olivier@gautherot.net) Received: from mail-px0-f182.google.com (mail-px0-f182.google.com [209.85.216.182]) by mx1.freebsd.org (Postfix) with ESMTP id 28A758FC1E for ; Tue, 12 Jan 2010 16:32:21 +0000 (UTC) Received: by pxi12 with SMTP id 12so15404888pxi.3 for ; Tue, 12 Jan 2010 08:32:17 -0800 (PST) MIME-Version: 1.0 Received: by 10.142.119.7 with SMTP id r7mr5876485wfc.261.1263312297252; Tue, 12 Jan 2010 08:04:57 -0800 (PST) In-Reply-To: <717f7a3e1001120714m37aada69gfaa35f0f9b17f435@mail.gmail.com> References: <717f7a3e1001120714m37aada69gfaa35f0f9b17f435@mail.gmail.com> From: Olivier Gautherot Date: Tue, 12 Jan 2010 13:04:37 -0300 Message-ID: To: Marin Atanasov Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-stable@freebsd.org, freebsd-hardware@freebsd.org Subject: Re: Multiple serial consoles via null modem cable X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 12 Jan 2010 16:32:22 -0000 Hi Marin, I'd like to ask you about the following - is it possible to have multiple > serial consoles coming from a single host? > In theory, no :-) RS232 is a point-to-point connection. If you want to feed several consoles through the same serial port, you will need some kind of switch to route the traffic to the corresponding port (whether the cable needs to be null modem or not wil depend on the switch itself). What I am talking about is connecting multiple machines using a null modem > cable - I know it is possible only to connect two machines and they need to > be connected on sio0 (COM1). > > I'm thinking about the following situation - 1 system acting like a host > with a serial port hub, each port of the hub is connected to a different > machine on sio0, using null modem cables. > > This would make the first machine something like a cheaper kind of a > terminal concentrator :) > The options that come up to my mind are: - a mechanical switch but it would not allow seamless routing (requires operator action to change channel) - a software switch using ESCAPE codes to change channel through an ad-hoc device driver - but there, make sure you don't miss bytes or the traffic may end up on the wrong terminal - if you fancy a home design, you could use the parallel port to send an address word but you will have to design your own seial port emulation on top of the standard sio0 to synchronize the signals... I would not bet too much on this one ;-) Also, evaluate if you need priority management: you may get to a situation where you need to send urgently characters to a terminal while another one has a long queue pending. In this case, you may be better off with Ethernet-to-Serial or USB-to-Serial converters. Hope it helps Cheers -- Olivier Gautherot olivier@gautherot.net Cel:+56 98 730 9361 www.gautherot.net http://www.linkedin.com/in/ogautherot