31.9 Peripheral and Generic Clock Controller

The PMC controls the clocks of the embedded peripherals by means of the Peripheral Control register (PMC_PCR). With this register, the user can enable and disable the different clocks used by the peripherals:

• Peripheral clocks (periph_clk[PID]), routed to every peripheral and derived from the Host clock (MCK), and
• Generic clocks (GCLK[PID]), routed to I2SC0 and I2SC1. These clocks are independent of the core and bus clocks (HCLK, MCK and periph_clk[PID]). They are generated by selection and division of the following sources: SLCK, MAINCK, UPLLCKDIV, PLLACK and MCK. Refer to the description of each peripheral for the limitation to be applied to GCLK[PID] compared to periph_clk[PID].

To configure a peripheral’s clocks, PMC_PCR.CMD must be written to ‘1’ and PMC_PCR.PID must be written with the index of the corresponding peripheral. All other configuration fields must be correctly set.

To read the current clock configuration of a peripheral, PMC_PCR.CMD must be written to ‘0’ and PMC_PCR.PID must be written with the index of the corresponding peripheral regardless of the values of other fields. This write does not modify the configuration of the peripheral. The PMC_PCR can then be read to know the configuration status of the corresponding PID.

The user can also enable and disable these clocks by configuring the Peripheral Clock Enable (PMC_PCERx) and Peripheral Clock Disable (PMC_PCDRx) registers. The status of the peripheral clock activity can be read in the Peripheral Clock Status registers (PMC_PCSRx).

When a peripheral or a generic clock is disabled, it is immediately stopped. These clocks are disabled after a reset.

To stop a peripheral clock, it is recommended that the system software wait until the peripheral has executed its last programmed operation before disabling the clock. This is to avoid data corruption or erroneous behavior of the system.

The bit number in PMC_PCERx, PMC_PCDRx, and PMC_PCSRx is the Peripheral Identifier defined at the product level. The bit number corresponds to the interrupt source number assigned to the peripheral.