8.4.6.8.3 GCLK Frequency Change Procedure

The GCLK frequency change procedure is as follows.

1. Wait for QSPI_SR.RBUSY=0 and QSPI_SR.HIDLE=1.
2. Send a QSPI_CR.LASTXFER command.
3. Wait for QSPI_ISR.CSRA=1.
4. Set QSPI_CR.QSPIDIS and wait for QSPI_SR.QSPIENS=0.
5. Disable the GCLK clock.
6. Change GCLK frequency.
7. Write QSPI_CR.QSPIEN.
8. Wait for QSPI_SR.QSPIENS=1.
9. If automatic refresh is enabled, wait for QSPI_ISR.RFRSHD=1 by polling or interrupt (see Automatic Refresh).