RFC: osmo-clk-gen v2

Harald Welte laforge at gnumonks.org
Tue May 21 09:37:07 UTC 2019


Hi Sylvain,

On Mon, May 20, 2019 at 05:13:42PM +0200, Sylvain Munaut wrote:
> > 2) allow different output voltages for two of the four banks of the Silabs chip
> >    https://osmocom.org/issues/3905
> 
> I'd use the DAC for software voltage tuning.
> Use 0R to select which bank uses which (default rail or programmable
> one, with just default to have 1/2 bank being the programmable vio).

Our solution so far was to have two banks fixed and two banks either
fixed or variable by means of (mechanical, tht) jumpers.  I'm not sure
we can fit our of them, or if we can fit 0R SMD resistors at lest. @Martin?

> > 3) should we keep the VCTCXO?
> 
> No.  As you explained I think it's better to split functions and not
> overload this board.

happy to see we're in agreement here.

> > 4) Use SAMD XOSC / PLL / GCLK to allow lower reference frequencies
> >    https://osmocom.org/issues/3857
> >    Where we'd actually use one of the SAMD GCLK outputs as one of the
> >    intputs to the Si5351C, and expose a GCLK input of the SAMD on an
> >    external header.  This way, much lower frequencies can be used to
> >    driver the Si5351C.  Or one could even go for deriving them from the
> >    SAMD RTC XTAL.
> 
> Does that mean the SAMD core would be running from the reference clock
> ? (and so wouldn't run if there is no reference connected)

The SAMD can run from its internal oscillator, even while communicating over
USB where it derives/recovers the USB clock from the SOF.  So while one could
run it from an external reference, it is not mandatory/required.

-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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