Re: [Discuss-gnuradio] About clock rate of USRP E100

[Philip Balister]

On 01/10/2011 09:25 AM, Miok Wah wrote:
> Hello list,
>
> We are planning to do some experiments with USRP E100. One advantage of E100
> that we are excited with is that
> "The user can choose (at run time) a convenient clock rate".
>
> Our question is:
> 1) When we change the clock rate changed, is the main clock rate changed, or
> is it just change in the decimation rate?
> We are asking this because we are interested in the energy consumption of
> USRP E100. The energy consumption is likely to be reduced if the main clock
> rate is reduced, but unlikely to be reduced if it's just change in
> decimation rate.

There are two clock rates to consider: there is the fpga clock rate 
which is settable via uhd. I'm not good enough at fpga's to know how 
much power can be saved this way.

The OMAP3 clock circuitry allows sections of the OMAP to be turned off, 
or clocked at lower rates to save power. This is how they use this chip 
in mobile devices. That said, the kernel and user space provided with 
the E100 has the clock rate set to the max possible and does not take 
advantage of the OMAP power saving features. It should be possible to do 
work in this area with the E100 though. There is lots of activity on the 
linux-omap kernel mailing list in the power management area.

Philip


> 2) How long does it take for the USRP E100 to stablize from one clock rate
> to another?
>
> Could you help clarify the problem if you know about the USRP E100?
>
> Thanks!!