Setting the Software Reset bit in CTRLA (CTRLA.SWRST=1) will trigger write-synchronization and set SYNCBUSY.SWRST. When writing a ‘1’ to the CTRLA.SWRST bit it will immediately read as ‘1’.
CTRL.SWRST and SYNCBUSY.SWRST will be cleared by hardware when the peripheral has been reset.
Writing a '0' to the CTRL.SWRST bit has no effect.
The Ready interrupt (if available) cannot be used for Software Reset write-synchronization.