Do panic

Raspberry Pi 2 running raspbian
I've run this Pi a few times, but recently I started to play with a bit
more, and fitted a Pi Cam to it. When I ran the config tool to enable
the camera, it said it had to reboot, at which point it started to
panic.
[ end Kernel panic - not syncing: VFS: Unable to mount root fs on
unknown block(179,2)
A bit of rummaging online found this thread :
formatting link

I tried the suggestion of changing the cmdline.txt file entry, but the
only difference that made was changing the block to 179,6).
which originally dated from 2013, but has a final posting from last
month suggesting that the problem hasn't been fixed.
Any suggestions on how to go ahead with this ?
Thanks
Adrian
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Adrian
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Have you seen the next to last posting? It mentions using a better/stronger power supply. I wonder if that might help as you have added new hardware.
Reply to
Stefan Enzinger
In message , Stefan Enzinger writes
That did cross my mind, but I'm using a 2 amp power supply, which I would hope would be more than enough. I wouldn't have thought that a Pi Cam would use that much power, but appreciate the extra straw on the camel's back situation.
Adrian
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Adrian
This is good advice. The camera takes a lot more power. It is possible that running with insufficient power may have corrupted the SD card. Worst case is it will need to be replaced and/or restored from your latest backup.
Reply to
Dom
But it's the possibility of voltage drop as current increases that may be an issue.
So "better" might mean "more stable under load".
John
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John Williams (News)
These days you need a PSU with a pedigree. Many of the inexpensive units are pure crap regardless of the current rating. Try putting a load on it and look at the voltage on a scope. You may see a lot of crap with low spikes that cause problems.
I bought a USB hub with a PSU. It dropped voltage with a 50 mA load. When I took it apart it only had a single transistor... no regulator chip at all.
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Rick
Reply to
rickman
In message , rickman writes
Thanks for the quick follow ups.
I don't have a scope, but I've a mate who has, who likes this sort of problem.
No back up on this Pi as it is pretty well still straight out of the box.
Adrian
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Adrian
I
Aye, dependant on how much copper there is (or isn't) between the PSU and Pi. Nominal power supply for a Pi is 5 V +/- 5% (4.75 - 5.25 V) at 750 mA (a booting Pi will pull that sort of current) it only takes 1/3 of an ohm to drop 0.25 V...
A Pi will work below 4.75 V but it's not really designed to and weird things may start to happen.
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Cheers 
Dave.
Reply to
Dave Liquorice
The problem isn't always that the rPi will have an issue itself, but that the voltage supplied to the USB connectors is marginal. Supply 4.82 volts to the USB connectors and the few milliohms of extra resistance in the current path drops the voltage more so that the attached devices are running out of spec. Add something that draws substantial current on the USB bus and this drops additional voltage in the PSU and inside the rPi making the whole unit run out of spec.
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Rick
Reply to
rickman
You can use a USB meter. They cost less than five dollars and there are dozens on eBay like this one . They are not particularly accurate but will show you if the voltage varies under load.
Reply to
Gordon Levi
You don't say if you have repeated the setup again and it now works. Or you have recreated the SD card from scratch and it fails every time with the camera attached.
It could be power related. The PSU spec suggests it up to the job but sadly Chinese manufacturers often lie on the specs. The other thing is with copper being so expensive, modern USB cables often contain more Pixie Dust and Unicorn's droppings than copper. Your PSU may be man enough but the cable is so poor there is a problematic voltage drop across it.
So what happens if you try to create the card from clean? If you unplug the camera can you create an SD card that works?
Reply to
mm0fmf
In message , mm0fmf writes
I haven't gone any further with this over the weekend, I've been doing other stuff. When I've had a chance to make a bit more progress, I'll report back.
Adrian
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Adrian
There is another possibility, which I've seen three times over a number of power supplies for various different equipment: the PSU might no longer be capable of providing the full rated output current. It could when new, but something has aged.
Yes, I've seen this too.
The USB specifications cover the cable itself in great detail, but only a minority of the USB cables I've seen actually conform to the specifications.
Dave
Reply to
Dave Higton

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