19.6.3.3.1 IDLE Mode

The IDLE mode allows power optimization with the fastest wake-up time.

The CPU is stopped.

The clock source feeding the GCLK generator 0, the GCLK generator 0, and the MCLK are kept active. The AHB/APB clocks are gated at the MCLK output, unless requested by a peripheral.

The other clock sources and the GCLK generators can be running or stopped depending on each clock source ONDEMAND bit, and depending on the peripherals requesting these clocks.

The CAN is a specific peripheral not featuring the AHB/APB clock request mechanism. As a consequence, it is clocked and can wakeup the system in IDLE0 mode, and not clocked and cannot wakeup the system in IDLE2 mode.

If an AHB/APB clock is masked in MCLK.AHBMASK or MCLK.APBxMASK, then it is gated at the output of the MCLK and not provided to the related peripheral (regardless of the related peripheral requesting it or not).

• Entering IDLE mode: The IDLE mode is entered by setting SLEEPCFG.SLEEPMODE = IDLE0/2 and executing the WFI instruction. Additionally, if the SLEEPONEXIT bit in the ARM Cortex System Control register (SCR) is set, the IDLE mode will also be entered when the CPU exits the lowest priority ISR. This mechanism can be useful for applications that only require the processor to run when an interrupt occurs. Before entering the IDLE mode, the user must configure the Sleep Configuration register.
• Exiting IDLE mode: The processor wakes the system up when it detects any non-masked interrupt with sufficient priority to cause exception entry. The system goes back to the ACTIVE mode. The CPU and affected modules are restarted.

In IDLE mode, the regulator and RAM operate in normal mode.