Hi to all.
I'm using Arduino IDE for the Atmel ATmega328PB Xplained Mini board. I download the skteches via an AVRISP MKII. Everything is working OK as long as I use the 5 Volt supply voltage.
When I switch to 3.3 Volt (via Jumper settings) the clock rate is automatically reduced from 16 MHz to 8 MHz at boot time. This causes all timings to be doubled, e.g. millis() resolution is now 2 ms, a serial interface must be initialized with 19200 Baud to work at real 9600 Baud, I2C transfer rate is halved, etc. So the system is still initialized for 16 MHz by the Arduino libraries.
I looked everywhere if I can find a setting, something like a clock divider, but was not able to solve the problem. Does anyone have an idea how to overcome the wrong timings at 8 Mhz?