Date: Sat, 23 Dec 2017 09:31:52 -0800 From: bob prohaska <fbsd@www.zefox.net> To: Bob Bishop <rb@gid.co.uk> Cc: freebsd-arm@freebsd.org, bob prohaska <fbsd@www.zefox.net> Subject: Re: Disapearing pl2303 usb serial adapter on rpi2 Message-ID: <20171223173152.GA25961@www.zefox.net> In-Reply-To: <F30A5C4C-E2F4-411E-8BAC-8356C1B985E8@gid.co.uk> References: <20171220170244.GA16029@www.zefox.net> <a312e6db-20ac-e12e-207e-1f0017cf8cad@gmail.com> <20171221161120.GA20324@www.zefox.net> <dfc17d98-a839-0ab9-2d1b-c47fe26be21e@selasky.org> <20171222041657.GA21799@www.zefox.net> <20171222173052.GA23984@www.zefox.net> <96d7cc41-33bf-1006-54a3-1cc8d9570fd2@selasky.org> <20171223001819.GB24362@www.zefox.net> <F30A5C4C-E2F4-411E-8BAC-8356C1B985E8@gid.co.uk>
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On Sat, Dec 23, 2017 at 04:55:56PM +0200, Bob Bishop wrote: > > Note that "The USB ports on a Raspberry Pi have a design loading of 100mA each...???[1] which is the absolute minimum allowed by the USB spec. ^^^^^^^ maximum? > > [1]https://www.raspberrypi.org/documentation/hardware/raspberrypi/usb/README.md > The PL2303TA data sheet at https://cdn-shop.adafruit.com/datasheets/DS_PL2303TA_d20120504.pdf claims the operating current is 10 mA maximum, plus output. The output drive rating is 4 mA, which puts the total far below the Pi's limit. The other USB loads on the RPI2 are a mouse, keyboard and Sandisk Extreme 64 GB USB flash drive, which holds /var, /usr /tmp and swap. The mouse is marked 5 V, 100 mA, the keyboard is marked 5 V 1.5 A, but contains a hub of its own, so I don't know how much power the keyboard itself uses. Both are old Dell units, it's fairly clear the keyboard rating includes outboard load and it's unlikely the mouse ever draws full nameplate current. A Logitech hubless keyboard is marked 100 mA, which seems a plausible upper limit for keyboard alone. The big mystery is the USB flash drive; I can't find any specs on power consumption, the only measure is a "touch test", which reveals the drive is lukewarm to the touch with a make session running in /usr/ports. I'd guess it's around half a watt, but that's only a guess. However, there has so far been no sign of misbehavior from the USB flash drive. Are there any software tools that can display USB power consumption? At the discovery of the USB/serial problems around a year ago there was a faint positional dependence; two of the hosts in the group seemed more prone to trouble than the other two when using the PL2303 adapters. That by itself suggested some sort of physical cause, but until Rod Grimes mentioned connector shroud grounding it never occurred to me to check. Having learned since that the shrouds weren't securely grounded I've resoldered one and installed it, not expecting it to make much difference since pin 4 _is_ securely grounded and the cables are unshielded anyway. That adapter has been up for 18 hours, a recent record, though by no means an all-time record. For the moment the best course seems to be waiting and watching. Thanks to everyone for reading! bob prohaska
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