Date: Tue, 21 Jun 2016 15:35:31 -0700 From: bob prohaska <fbsd@www.zefox.net> To: James Elstone <james.c.elstone@gmail.com> Cc: freebsd-arm@freebsd.org, bob prohaska <fbsd@www.zefox.net> Subject: Re: pl2303 lockups on rpi2 Message-ID: <20160621223531.GC2449@www.zefox.net> In-Reply-To: <CANocirkCFXr8zDQZQv_Cm6j4UYDFHEuvQ2Fwn7wmwPuqkvTWaw@mail.gmail.com> References: <fbsd@www.zefox.net> <20160619020311.GC38492@www.zefox.net> <20160619034248.1D097406057@ip-64-139-1-69.sjc.megapath.net> <20160621041439.GA2449@www.zefox.net> <CANocirkCFXr8zDQZQv_Cm6j4UYDFHEuvQ2Fwn7wmwPuqkvTWaw@mail.gmail.com>
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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 > Kr, > > James > > P.s. Would you know the state of support with a RP3? > On 21 Jun 2016 05:14, "bob prohaska" <fbsd@www.zefox.net> wrote: > > > On Sat, Jun 18, 2016 at 08:42:48PM -0700, Hal Murray wrote: > > > > > > > > > The Linux geeks have figured out how to use the "console" as a serial > > port. > > > It's used by the GPS HATs. If you are trying to get work done rather > > than > > > debug USB stuff, that might be an interesting approach. You would need a > > > level shifter if you are talking to a real RS232 device. > > > > > The goal is simply to let one Pi monitor the console of another, thus > > making > > single user mode accessible over a network. > > > > After a recent lockup on the usb-serial adapter, I was very surprised to > > find > > the pl2303ta "came unstuck" when the serial cable connecting to the > > console port on the > > next Pi in the chain was disconnected. No need to unplug the USB side. > > > > Thanks for reading, > > > > bob prohaska > > > > > > > > > > _______________________________________________ > > 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" > >
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