The IPC, Shared RAMs, and Message RAMs are clocked by PLLSYSCLK. EPI is clocked by M3SSCLK. The PLLSYSCLK normally refers to the output of the Main PLL divided-down per the SYSDIVSEL register. In case the PLL is bypassed, the PLLSYSCLK becomes the OSCCLK divided-down per the SYSDIVSEL register. In case of a missing source clock, the 10MHZCLK is substituted for the PLLSYSCLK.
Although EPI is a shared peripheral, it is physically located inside the Cortex-M3 Subsystem; therefore, EPI is clocked by M3SSCLK.