Clock Sources and Clock Generators

In order to reduce the power consumption for an application, all unused clock sources should be disabled. Peripherals often require to run on different frequencies in an application, which often results in different clock sources being used for the different peripherals. As the number of enabled clock sources increases, as will the power consumption.

Devices from the SAM D and SAM L series have a generic clock controller (GCLK) which contain several generic clock generators, refer to Figure 1 for GCLK implementation in SAM L series. One clock source can source several generic clock generators, and each generator can divide the clock source separately in order to get different frequencies. Choosing this solution, one can achieve several frequencies without the penalty of several clock sources being enabled. In addition, the clock system on devices from the SAM D and SAM L series allows for the clock source to be automatically turned off when not requested by a peripheral. Achieving this functionality is done by writing a one to the On Demand Control (ONDEMAND) bit for the corresponding clock source.

Figure 1. Device Clocking Diagram