I am working with a curiosity nano (with atmega4809). LED blinking w/ delays seems to indicate that the clock rate is not 16 MHz or 20 MHz.
The nano literature indicates that the 4809 is being operated at 3.3 V.
The 4809-48 data sheet says the CPU clock max frequency can be 10 MHz at room temperature.
The 0-series datasheet indicates MCLKCTRLB resets the clock to divide by 6.
The best I can guess is that if the osc rate is 16 MHz, the CPU clock starts at 2.666 MHz, of if osc at 20 MHz the CPU clock starts at 3.333 MHz.
Does anyone know what this is?
My next step would be to go off and write code to toggle a pin and hook up a scope.