Clock configuration

Clock hardware definitions are in atmega328p::clock. The selected board frequency belongs in MCUConfig.h.

Expected CPU frequency

#define MCU_CLOCK_HZ 1000000UL

This is the expected CPU frequency immediately after reset. It is not necessarily the oscillator's raw frequency: CKDIV8 or another clock prescaler may divide the source.

For the documented factory reference, the internal calibrated RC oscillator is nominally 8 MHz and CKDIV8 is programmed, giving a nominal 1 MHz CPU clock after reset.

Available definitions

Use mcu::clock::Source, CKSELCode, SUTCode, and Prescaler to identify the clock choices. Constants such as internal_calibrated_rc_hz, internal_128khz_rc_hz, and factory_default_cpu_hz describe the device.

The library does not calculate fuse bytes from the selected clock, configure CLKPR, or change the physical clock. Keep MCU_CLOCK_HZ consistent with the intended fuse bytes and board oscillator.