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Author Topic: Unstable USB  (Read 4245 times)
karurosu
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« on: May 25, 2009, 10:21:13 PM »

As I have posted in other threads, whenever there is some kind of electrical noise my plug's usb start to fail. This has already happened with the following events:

-Turning on a lamp which is failing that crackles and blinks a lot.
-Touching the usb hub while connecting another cable.
-The microwave while cooking popcorn (the microwave is quite far from the plug, maybe 5 meters, and there are 2 walls between them)

Whenever it happens, the usb kinda resets, and my USB flasdrive is assigned a different device file, and since its my root, everything fails and I have to hard reset, pretty annoying :/
What I find interesting is that the power has failed for a split second and the plug kept working afterward like nothing happened.

I am not sure what to blame,I suspect the power, right now it is only connected to a power strip, I want to get an UPS soon, would that solve my problem?
Another suspect is plain old EM noise on the air (especially when the other devices around), but I just can't point a solution, except get the UPS.

Btw, I know that the hub is not a problem since it also happened while I was nos using it (flash drive connected directly to the plug).

Any suggestion? It's driving me crazy, since I can't get it to be more than 2 days without crashing (record is at around 1 day 20 hours).
Thanks.
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restamp
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« Reply #1 on: May 26, 2009, 09:03:09 PM »

I suspect whether a UPS would be helpful would depend a lot on the UPS.  Some provide fairly good power-line conditioning while running off the mains and some don't do anything but bridge the line through unfiltered as long as there is usable external power.  Also, bear in mind that the vast majority of UPSs will introduce a small glitch when transitioning to battery and back again to the mains.  These glitches typically last only a few ms, and can't be helped because the UPS needs some time to determine that the line power has gone off-normal and respond.  It then must fire up its own circuitry, often meaning there are several cycles of substandard power before things settle down.  And most inexpensive UPSs do not produce anything close to a sinusoidal waveform.  It is presumed that most computer power supplies have plenty of internal capacity to absorb all these things in stride (and most do).  If your plug's power supply is particularly sensitive, though, any of these might be enough to cause the corruption you'd like to avoid.

Question: what is your voltage?  I'm wondering if perhaps it is operating at the lower end of the plug's limit.  Do you have access to a variac?  If so, and if your voltage is low, you might try increasing the voltage by, say, 10% and seeing if that has an effect on things.

Good luck!
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karurosu
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« Reply #2 on: May 26, 2009, 09:29:11 PM »

Hi, thanks for the answer. As of my voltage its supposed to be 120, however I am not sure what the exact measure is, I am going to try measuring it later. I don;t know what a variac is, sorry :S

As of the USP, I was planning on getting one of these: http://www.apc.com/resource/include/techspec_index.cfm?base_sku=BE350G
Its not expensive, and I think APC is a good brand.

Anyway, I am not really sure were the problem lies, it simply happens out of a sudden, but I've found that the pattern is related to those events I described earlier. Maybe the problem is like you say, that I am working on the lower end of the limit, because when I turn on the microwave or the lamps, all the lights at my house kind of lose intensity.
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karurosu
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« Reply #3 on: May 27, 2009, 10:20:58 PM »

As a bit of an update, I replaced the hub (an unpowered perfect choice brand) for the one that was bundled with rockband for xbox 360 (4 ports, self powered) and so far everything has been working ok, the current uptime is 1 day 3 hours.
I suspect the problem is that the sheeva barely has enough power to drive the USB hub, and when a brownout happens the devices restart.
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restamp
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« Reply #4 on: May 27, 2009, 11:18:45 PM »

Super.  Hope your new USB hub proves reliable.  Have you tested it against the microwave and your recalcitrant light yet?

FWIW, a variac is a device -- an autotransformer wound around an iron toroid with a slider that serves as a tap -- which allows you to vary the AC line voltage, from zero to typically around 140V for a nominal 120V feed.  It's what they used to use before the advent of large power solid state devices to control/dim stage lighting, etc., and it can be mighty useful in diagnosing a shorted piece of electronics as well as for analyzing problems having to do with line voltage.
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semery
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« Reply #5 on: May 28, 2009, 09:29:10 AM »

Super.  Hope your new USB hub proves reliable...

I was having a similar problem and I just dug up an old (circa 2000) self powered USB 1 hub and my USB key seems to be working just fine. No more problems like I was describing here: http://plugcomputer.org/plugforum/index.php?topic=349.0. So other than the fact that I'm running at 12Mbps, everything seems to be alright. I might have to go out and get a newer and less bulky hub.

Hopefully the USB system will get beefed up in a future hardware revision!
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restamp
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« Reply #6 on: May 28, 2009, 01:14:26 PM »

I'd be curious to understand whether the problems you were experiencing that were ameliorated by the powered hub were caused by the hub being able to provide more power to the devices, or whether it was the forcing of the USB connection to USB1 speeds that resolved them.  (If it is the latter, that is not necessarily a good sign.)
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karurosu
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« Reply #7 on: May 28, 2009, 01:22:31 PM »

Mine were solved by using a powered hub. Since my specific problem were resets when power problems.
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semery
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« Reply #8 on: May 28, 2009, 04:15:36 PM »

I'd be curious to understand whether the problems you were experiencing that were ameliorated by the powered hub were caused by the hub being able to provide more power to the devices, or whether it was the forcing of the USB connection to USB1 speeds that resolved them.  (If it is the latter, that is not necessarily a good sign.)

I'm pretty sure it was the former. I picked up a powered USB 2 hub and the drive is now running well (as my root fs) at full speed.  Grin
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