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Author Topic: Sensors, Power Management, Clock Speeds and Memory  (Read 2200 times)
gordan
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« on: December 20, 2010, 04:25:53 PM »

I have a few questions:

1) Are there any built in sensors (e.g. temperature) that are accessible via lm_sensors or similar on the Sheeva Plug? Some probes cause a lock-up crash, others find nothing. Are there any sensors?

2) Is there a way to adjust the clock-seed at run-time on the Sheeva? I notice that most ARM based Android phones work with an application called SetCPU that allows the CPU to be underclocked to improve battery life and overclocked to improve performance. Are there controls available on the Sheeva to do this? Can it work with the cpuspeed package/daemon to improve idle power savings? I norice the kernel enables the cpuidle ladder and menu governors. How does this compare to the x86 equivalents such as EIST on the Atom? When under-clocking to save power, is there a way to drop the CPU voltage at the same time to save even more power like with EIST? Since ARM is all about power efficiency, I'm hoping such features exist.

3) I can see in the Kirkwood spec that it supports up to 2GB of RAM. Does anyone know what chips could be used to upgrade a Sheeva to 2GB? I'll take my chances with my soldering skills, but I need to know what chips would work.
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doragasu
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« Reply #1 on: January 05, 2011, 09:52:06 AM »

I can only answer to the second question, and the answer is NO.

I asked it in this forum some months ago, and got no answer, so I started investigating, downloaded the CPU datasheet and found that CPU speed is configured in HARDWARE and can't be changed by software. GP power saving is really primitive, and can only reduce a bit of power consumption during idle CPU loops, but doesn't reduce neither CPU speed nor CPU voltage.

I was really disappointed when I found this, because I was previously working with beagleboards (featuring the powerful and power saving OMAP3 chip by Texas Instruments) and with this chip, the PLL multipliers (and thus the CPU speed) can be changed in software on the fly. The Linux cpufreq module does a great job with this CPU using the ondemand scaling governor, and whith light or medium CPU load the power consumption can be really reduced. Also the chip the beagleboard uses to supply power to the OMAP3 processor drops the CPU voltage according to the selected speed...

It's a pity GlobalScale used the Marvell chip instead of the TI one, they could have saved a lot of heat problems, some space (due to the PoP CPU+Memory packages) and could have cut the power consumption even more.
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doragasu
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« Reply #2 on: January 07, 2011, 09:36:47 AM »

I stated earlier I could only answer the second question, but as nobody answers the others, I can try to give you some tips on the other two.

1) I have never searched sensors, but Guruplug has a U-Snap connector, and I suppose sensors are one of the main applications of this connector. I think Sheevaplugs don't have this connector, but I may be wrong.

3) Again, I can only give you a tip about this. I don't know what chips do you have to use, but I doubt you can solder them, because the footprints are BGA with a very low pitch between balls. You need a special oven to solder this kind of chips, a stencil with the exact positioning of the pads, solder paste... and even with this equipment, it's relative easy to damage the board in the process...
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gordan
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« Reply #3 on: January 09, 2011, 05:44:10 AM »

Thanks for responding, I appreciate it.

Regarding the RAM soldering, I wouldn't be doing it myself, I would be sending it to a specialist shop to do the work with proper industrial soldering equipment. In the past they upgraded the RAM in my HTC Universal from 64MB to 128MB without any problems, and I expect this would be similar.
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