13.9.6.9 Synchronization

DFLL48M

Due to the multiple clock domains, values in the DFLL48M control registers need to be synchronized to other clock domains.

Once the DFLL is enabled, any read and write operation requires the DFLL Ready bit in the Status register (STATUS.DFLLRDY) to read '1'.

Note: Once the DFLL48M is enabled in on-demand mode (DFLLCTRL.ONDEMAND=1), the STATUS.DFLLRDY bit will keep to '0' until the DFLL48M is requested by a peripheral.

Before writing to any of the DFLL48M control registers, the user must check that the DFLL Ready bit (STATUS.DFLLRDY) is set to '1'. When this bit is set, the DFLL48M can be configured and CLK_DFLL48M is ready to be used. Any write to any of the DFLL48M control registers while DFLLRDY is '0' will be ignored.

In order to read from the DFLLVAL register in closed loop mode, the user must request a read synchronization by writing a '1' to the Read Request bit in the DFLL Synchronization register (DFLLSYNC.READREQ). This is required because the DFLL controller may change the content of the DFLLVAL register any time. If a read operation is issued while the DFLL controller is updating the DFLLVAL content, a zero will be returned.

Note: Issuing a read on any register while a write-synchronization is still on-going will return a zero.

Read-Synchronized registers using DFLLSYNC.READREQ:

DFLL48M Value register (DFLLVAL)

Write-Synchronized registers:

DFLL48M Control register (DFLLCTRL)
DFLL48M Value register (DFLLVAL)
DFLL48M Multiplier register (DFLLMUL)

DPLL96M

Due to the multiple clock domains, some registers in the DPLL96M must be synchronized when accessed.

When executing an operation that requires synchronization, the relevant synchronization bit in the Synchronization Busy register (DPLLSYNCBUSY) will be set immediately, and cleared when synchronization is complete.

The following bits need synchronization when written:

Enable bit in control register A (DPLLCTRLA.ENABLE)
DPLL Ratio register (DPLLRATIO)
DPLL Prescaler register (DPLLPRESC)