17 Jul
2012
17 Jul
'12
2:54 p.m.
Hi all,
On Sun, Jul 15, 2012 at 11:51:22PM +0200, Harald Welte wrote:
More interesting is the clock source, where I would
like to see a
switchable clock source between:
* regular inetrnal VCTCXO
* external clock input (U.FL)
on the compal phones, a stand-alone oscillator (with control input) is
used, so I think you'll want to copy that. There are tiny single gate
multiplexers (e.g. 74LVC1G157) where NXP specifies a propagation delay
of 13ns max (125°C temperature, 1.65V supply), so it should certainly
work at 26Mhz (RITA's input wouldn't need the full voltage swing
anyway).
Does anyone have a good idea how to implement the
actual switch? I
think it would be best to have it software-switchable from a GPIO...
Switching the clock will produce a glitch, but we should be able
to run the ARM core from the 32kHz clock crystal during that period,
I think (but will have to check) would we really want to toggle
between the two inputs? Do we want to autodetect a valid ext. refclock?
On Mon, Jul 16, 2012 at 10:11:50PM +0200, Mathias K. wrote:
The micrel parts are really impressive, but much too fast for our
purpose (>2GHz).
Chris