Plug computers

[Lennart Sorensen]

On Wed, Aug 25, 2010 at 02:51:29PM -0400, D. Hugh Redelmeier wrote:
> | From: Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org>
> 
> | It takes a lot more power to operate at 1Gbps than at 100Mbps.
> | So actually it does make sense.  A fairly common estimate seems to be
> | about 100mW for 100Mbit, 1W for gigabit and 10W for 10Gbit.  Or at least
> | in that order of magnitude.
> 
> Interesting.  Thanks for the information.
> 
> 1w extra isn't a lot to dissipate but this is a very passive design.

Well if you have a system without a fan that normally gives off 2 or 3
watts, but gives off 4 watts if you run everything maxed out, that is
a large increase.

> This document is about the central chip: 
> <http://www.marvell.com/products/processors/embedded/kirkwood/HW_88F6281_OpenSource.pdf>
> The PHY for ethernet is off-chip.  I have no idea what PHY thermal 
> characteristics might be.

I am not sure how much heat comes from the PHY versus the MAC.

> Section 8.3 deals with thermal power dissipation.  Eyeballing, it
> looks like the chip only dissipates two or three Watts and that the
> non-PHY ethernet power isn't broken out or if it is, it isn't much.
> 
> Looks like a pretty remarkable chip.  Too bad the CPU core isn't as
> well supported as newer ARMs.

Well I have seen lots of activity in Debian for the sheeva boxes, so I
wouldn't say they aren't well supported.  The lack of FPU is unfortunate
I think, but the rest seems decent.

> Looking at
> <http://www.globalscaletechnologies.com/t-guruplugdetails.aspx> I
> would guess that the main thermal problem is that the power supply is
> in the same package.  Convenient, but it adds a fair bit of heat to
> dissipate.  Especially if a couple of USB devices are drawing a lot of
> power (max is 500mA * 5V * 2, close to 5W).

Certainly doesn't help.

-- 
Len Sorensen
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