21.5.1 Principle of Operation

The CLK_MAIN clock signal from the GCLK0 module is the source for the main clock, which in turn is the common root for the synchronous clocks for the CPU, APBx (Advanced Peripheral Bus), and AHBx (Advanced High-performance Bus). The CLK_MAIN is divided by an 8-bit prescaler. Each of the derived clocks can run from any divided or undivided main clock, ensuring synchronous clock sources for each clock domain. The clock domain (CPU, LP, BUP) can be changed on the fly to respond to variable load in the application as long as f_CPU ≥ f_LP ≥ f_BUPf_CPU ≥ f_BUP. The clocks for each module in a clock domain can be masked individually to avoid power consumption in inactive modules. Depending on the sleep mode, some clock domains can be turned off.