Schematic for Omega2
Are there schematics available for the Omega2?
No, that is one of the many obvious things still inexcusably missing.
The schematics for the SoC maker Mediatek's own Linkit Smart module are available though, if you want to get an idea of a similar system.
@Chris-Stratton I was looking at that already and the docs for the MT7688 are pretty light for a MPU.
The first thing stands out is the oscillator circuit. I have not seen one like it before and not even sure how it works. It's certainly not your typical xin/xout with load caps.
@Chris-Stratton Has there been other discussion about this? I'm pretty new to the community. Is it another case of a company wanting the benefits of open-source communities without the risks contributing to it themselves?
the docs for the MT7688 are pretty light for a MPU
I would suspect that Mediatek thinks of it not as an MPU, but an SoC designed to be a wifi router or a few related types of media boxes.
Crystals typically have two closely spaced but distinct resonances, and are intended and specified for use at one or the other in compatible type of circuit. The "Xin/Xout" style would likely be operating in a series resonance mode, while the one side grounded would be operating in parallel one. To get an accurate frequency you would need one cut for the resonance mode intended to be used.
If you are designing your own board at more than "see if I can" level you probably need to be in contact with Mediatek - not only for details, but to arrange a supply of chips. For an experiment, just transplant the crystal along with the chip.