In Run Mode, the Cortex-M3 processor, memory, and most of the peripherals are clocked by the M3SSCLK, which is a divide-down version of the PLLSYSCLK (from Main PLL). The USB is clocked from a dedicated USB PLL, the CAN peripherals are clocked by M3SSCLK, OSCCLK, or XCLKIN, and one of two watchdogs (WDOG1) is also clocked by the OSCCLK. Clock selection for these peripherals is accomplished through corresponding peripheral configuration registers. Clock gating for individual peripherals is defined inside the RCGS register. RCGS, SCGS, and DCGS clock-gating settings only apply to peripherals that are enabled in a corresponding DC (Device Configuration) register.
Execution of the WFI instruction (Wait-for-Interrupt) shuts down the HCLK to the Cortex-M3 CPU and forces the Cortex-M3 Subsystem into Sleep or Deep Sleep low-power mode, depending on the state of the SLEEPDEEP bit of the Cortex-M3 SYSCTRL register. To come out of a low-power mode, any properly configured interrupt event terminates the Sleep or Deep Sleep Mode and returns the Cortex-M3 processor/subsystem to Run Mode.