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Author Topic: Under Clocking a Guru Plug  (Read 2930 times)

robmoss

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Under Clocking a Guru Plug
« on: 30 April 2012, 09:14:14 pm »

Hi All,

I am wondering if anyone knows how to underclock a Guru Plug. I have looked into using cpufreq tools but I cannot seem to find the Kirkwood cpu driver, although others seem to have managed this. I was also wondering if there was a hardware fix that anyone might know of, along the lines of a jumper or lifting a track.

We have working plugs, but sometimes when we download from USB to an nfs share we lock up the guru plug. Some judicious Googling lead me to a mail list that was talking about unstable USB and there was conjecture that dropping the processor speed slightly might resolve the issue. It seems a logical quick step, though I seem to be stuck at the first jump so maybe not so logical.

Thanks for your time and your advice.

Best regards,

Rob Moss.
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Confusticated

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Re: Under Clocking a Guru Plug
« Reply #1 on: 30 April 2012, 10:51:21 pm »

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Kirkwood cpu driver
It's a kernel source patch under the guise of 'power saving' (Google should find it)

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a hardware fix
Refer to the Schematics, the logic applied to specific MPP lines at hardware startup control the clock frequency (possibly the issue with the 'recalled plugs' running at 400MHz instead of 1200MHz)

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conjecture that dropping the processor speed slightly
Sounds very dubious way of fixing 'unstable USB' to me, clock frequency choices are fixed at either 1200 or 400 MHz.

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to an nfs share
Have you tested with a different file system type (not ntfs-3g or fuse) to see if it still locks up?
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robmoss

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Re: Under Clocking a Guru Plug
« Reply #2 on: 01 May 2012, 04:32:37 pm »

Hi Confusticated,

Thanks for the information. I will start on tracking down the Kernel patch.
I have looked at the Schematics and am wondering whether that is the way to go. I am thinking that a software approach may be more precise than hardware.
It does sound a bit odd, but the mail list I was reading ran for about 4 months and dealt with an arm processor and a USB issue just like we are seeing. There was a good deal of environmental testing and they seemed to come to the conclusion that there was a race condition in some boards and that dropping the clock cycles would stop this condition. My thoughts are that it may be worth a shot if we can easily under clock.
We have not tested with another file system type, but that will now be another approach we can take.
Thanks for your time and advice.
I will report back with what we find if you are interested.
Best regards,
Rob Moss.
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Confusticated

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Re: Under Clocking a Guru Plug
« Reply #3 on: 01 May 2012, 06:57:47 pm »

For the least amount of pain (easier to roll out or revert than a hardware hack)...

With the kernel patch applied, in the kernel configuration enable 'CPU Power Management->CPU Frequency Scaling->ARM CPU frequency scaling drivers->Kirkwood SoC'
Select the 'CPU Power Management->CPU Frequency Scaling->powersave governor' option as the default to fix the SoC CPU to 400MHz.

Quote
I will report back with what we find if you are interested
Yes please
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