[avr-chat] Urgent clock-related questions

[Rick Mann]

So, I just found out that I designed my board with a 32.768 kHz crystal 
connected to the XTAL pins, rather than the TOSC pins. The problem is that to 
move it, I lose my only available SPI port (this is an ATxmega256A3U, and all 
the other SPI port pins are being used for something else).

The easiest solution will be to use a MHz-speed crystal instead of a 32 kHz 
crystal. I don't need low power operation. But I'm not sure I can calibrate the 
internal oscillators via DFLL using an external crystal; the docs talk about 
external clock.

There doesn't seem to be a way to drive the RTC from the XTAL pins, nor can you 
calibrate the internal 32 kHz clock from an external crystal (on XTAL1 & 2).

I don't really need RTC.

So, I guess the best thing is to just stick a 16 MHz crystal on the XTAL pins 
and be done with it? I need USB. If I understand things correctly, I can PLL 
that up to 96 MHz, then divide by 2 to get 48 MHz.

If I'm wrong, please let me know.

Thank you!

-- 
Rick