Many devices have xtal in/out connections that require a crystal, caps, and resistor to generate the system clock. Most(?) document the option to use an external oscillator as one of the inputs and, usually, recommend/require the other signal tied to ground. I’ve always liked this clean option. In my earlier years of micro development sometimes matching the components was problematic.
Does SophGo recommend or allow this? If so, details of connections and voltage supply for oscillator to make it work.
I don’t see why not (although I’m not sure it’s at all justified - using a crystal and 2 caps is fine and shouldn’t give you any problem).
You’ll just have to connect the output of some oscillator to the XTAL_IN pin. You can refer to the schematic of the Duo board(s).
Note that the typical frequency is 25 MHz, and that the XTAL_IN(/OUT) pin is in the VDDIO_RTC domain, as far as I can tell from the datasheet, and VDDIO_RTC is 1.8V typical (1.98V max from the DS). So, your oscillator will have to be powered @ 1.8V.
Also note that as a potential “downside”, using an external oscillator, said oscillator will keep running even when the chip is in a low-power mode that would otherwise shut down the internal XTAL oscillator, so you’ll be losing that “feature”.
I’ve seen differing definitions of xtal in/out, clkin/out, xtal1/2 with the other pin floating or grounded. Would appreciate a MILK-V FAE definitive answer if one hangs out here.
Appreciate oscillator overhead, my boards are usually running if powered on by the mains. I’ll probably just use xtal, caps, resistor like everyone. A sleep mode with RTC wakeup might be useful, but powered on operation is default.
