From owner-freebsd-arm@freebsd.org Wed Jun 22 00:46:36 2016 Return-Path: Delivered-To: freebsd-arm@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 0BAA1AC5233 for ; Wed, 22 Jun 2016 00:46:36 +0000 (UTC) (envelope-from james.c.elstone@ntlworld.com) Received: from know-smtprelay-omc-11.server.virginmedia.net (know-smtprelay-omc-11.server.virginmedia.net [80.0.253.75]) by mx1.freebsd.org (Postfix) with ESMTP id 52D6016DD for ; Wed, 22 Jun 2016 00:46:34 +0000 (UTC) (envelope-from james.c.elstone@ntlworld.com) Received: from THORIUM ([82.2.189.134]) by know-smtprelay-11-imp with bizsmtp id 9clQ1t00H2uRS4201clQiE; Wed, 22 Jun 2016 01:45:24 +0100 X-Originating-IP: [82.2.189.134] X-Spam: 0 X-Authority: v=2.1 cv=OJTapnuB c=1 sm=1 tr=0 a=veQ/QFbREZPQBKeuBCmuXw==:117 a=veQ/QFbREZPQBKeuBCmuXw==:17 a=L9H7d07YOLsA:10 a=9cW_t1CCXrUA:10 a=s5jvgZ67dGcA:10 a=kj9zAlcOel0A:10 a=6I5d2MoRAAAA:8 a=7QypooQz5QXDWeewLhEA:9 a=lUVFcQCXJ7cUTMjV:21 a=KXZs7l5hMYCt3NOH:21 a=CjuIK1q_8ugA:10 a=IjZwj45LgO3ly-622nXo:22 From: "James C Elstone" To: References: <20160619020311.GC38492@www.zefox.net> <20160619034248.1D097406057@ip-64-139-1-69.sjc.megapath.net> <20160621041439.GA2449@www.zefox.net> <20160621223531.GC2449@www.zefox.net> <1466551193.34556.76.camel@freebsd.org> In-Reply-To: <1466551193.34556.76.camel@freebsd.org> Subject: RE: pl2303 lockups on rpi2 Date: Wed, 22 Jun 2016 01:45:38 +0100 Message-ID: <000001d1cc1f$656511b0$302f3510$@c.elstone@ntlworld.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: AdHMFVfOC3QjkuqQRVCK2VtOVdB9XAAB6UpQ Content-Language: en-gb X-BeenThere: freebsd-arm@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: "Porting FreeBSD to ARM processors." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Jun 2016 00:46:36 -0000 Hi Bob, Just a few more thoughts to ponder: It may be an idea to check the status / strength (voltage) of the TX>RX / RX On Tue, Jun 21, 2016 at 10:34:41PM +0100, James Elstone wrote: > > Hi Bob, > > > > What sort of flow control (rts/cts, xon/xoff, or none)? > > > > I suspect you cleared the control signals rather than unfreeze?? > > There are none to clear: The serial end is on an RPI2, with only TX, > RX and ground. The USB end is on a second RPI2. > > In that particular case, I tried unplugging and replugging the USB > end, to no avail. Then I dragged over an iMac with Prolific's drivers > installed and plugged the USB end into the iMac. The > PL2303 still wasn't recognized. While it was still plugged into the > iMac, I lifted the TX, RX and ground connections on the PL2303 cable. > The PL2303 recognition message immediately showed up on the iMac's > console. > > As it happens, the two RPI2s in question share a ground through the > wired Ethernet. They're connected to two different switches, which are > in turn connected by a length of cable. > > The ground cable on the PL2303 forms a second, parallel ground, > amounting to a loop. This is universally considered bad practice but > is often gotten away with. Perhaps I'm not so lucky. > > The Prolific driver installation instructions specify installing the > software, connecting the USB end next and connecting the serial end > last. I thought they were just pacifying the pedantic among us, but > maybe there's a physical reason behind the advice. > > Next time a PL2303 locks up I'll begin by lifting the serial cable > connections, ground first, to see what the uplcom driver does. If it > subsequently recognizes the PL2303 I _think_ that supports the notion > of a wiring problem. > > Thanks for reading and special thanks to Hal Murray for introducing > the idea of serial devices being "held" by signaling voltages, > > bob prohaska > If the serial side has active signals and the usb side is unconnected then you are essentially applying power to some of the IO pins of an otherwise unpowered chip. Sometimes you end up accidentally powering the chip that way and it kinda-sorta works. Other times it just fries the chip. And sometimes it's harmless (usually only because the active signal line(s) can't source enough current to cause any harm). -- Ian _______________________________________________ freebsd-arm@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-arm To unsubscribe, send any mail to "freebsd-arm-unsubscribe@freebsd.org"