Date: Mon, 1 Jan 2018 10:23:47 -0800 (PST) From: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net> To: bob prohaska <fbsd@www.zefox.net> Cc: freebsd-arm@freebsd.org Subject: Re: Disapearing pl2303 usb serial adapter on rpi2 Message-ID: <201801011823.w01INlRV087478@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <20180101181046.GA7042@www.zefox.net>
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> On Sat, Dec 23, 2017 at 11:11:20AM -0800, bob prohaska wrote: > > > > Thanks for your attention, and apologies for what's beginning to > > look like a red herring! > > > > Well, the ungrounded USB shroud wasn't the problem. The pl2303ta locked > up again. Unloading and reloading uplcom didn't help, unplugging the USB > connector and waiting several minutes didn't help. > > However, unplugging the USB connector and plugging it into a powered hub > _with_the_power_off_ did unstick the adapter. Probably the hub loaded down > what little power could backfeed from the downstream serial port to turn > the chip fully off. When reinserted in the RPI2 the adapter was recognized > and seems to be working normally for now. > > It's rather clear the pl2303ta is latching up, but why it's worse on a > -current machine than it is on an 11-stable machine is less obvious. One > difference between the two is USB activity; the -current box uses a USB > flash drive for most of the filesystems, along with a seldom-used mouse > and keyboard. The -stable machine has all storage on the microSD card, > no mouse and no keyboard. > > Thanks for reading, and any ideas. I would try disconnecting the gnd lead at the rs-232/ttl point, and connect all 4 RPI's directly togeather with a nice ground daisy chain with as short a wire as practical. And preferably with something larger than the 30gage wire or so that is in these USB/RS-232 adapters. Something like 24 gauge. The change in versions -could- be additional or different signal activity on the board(s) changing the amount of generated noise, might be interesting to see if there is a difference in power consumption between the 2 revisions, and or temperature level of the SOC (indicating power usage change indirectly). Trying to run logic between boards with low quality grounding is in general just asking for flakey things to happen. -- Rod Grimes rgrimes@freebsd.org
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