Add support for precision XTAL/TCXO

[mungewell]

For my own project, I needed a more accurate XTAL... obviously not everyone needs this, or wants to spend the extra money. However there is a nice 'hack'.

By adding 2 resistor footprints to connect to pin 2 of the XTAL, 'we' could configure the board to take either a passive XTAL or a (user performed modification) TCXO. Only extra one resistor, connecting to ground, would be fitted for mass production.

Would you consider adding this?

More info on what I am doing.
mungewell/pico-timecode#4

[diminDDL]

While it looks interesting, there is some hustle associated with re-routing the board for this admittedly niche use case, I will leave the issue open and in case there will be more support/requests I'll consider it.

[diminDDL]

Upon further thought I think I might add it at some point in a similar way as described where it can be optionally populated as needed.

[mungewell]

Cool, thanks. I'm sure that there are others out there would also benefit.

I'm working on some automated testing, using uhubctl to cycle boards on/off and perform calibration process with my. This should help document variance between stock XTAL and TCXO...

[mungewell]

After being busy with other stuff this summer, I have restarted work on my Pico-Timecode project and have some test data showing how the stock XTAL is behaving.
mungewell/pico-timecode#4 (comment)

I appreciate not everyone needs this level of precision... My particular needs are sub-1PPM accuracy over varying temp, so a TCXO is probably a must.