67.4.2.2 Backup Mode with DDR in Self-Refresh

Backup mode with DDR in Self-refresh is used to keep the DDR contents when the system is powered off. This mode is achieved by maintaining the backup area and the VDDIODDR powered. To enter Backup Self-refresh mode, follow the sequence below:

Software saves all the context information to resume (application-dependent).
Put the DDR in Self-refresh mode and wait until the Self-refresh status is OK (refer to the section Multiport DDR-SDRAM Controller (MPDDRC)).
Set SFRBU_DDRBUMCR.BUMEN (see SFRBU DDR BU Mode Control Register).
Enter Backup mode as described above.

To exit this mode, follow the sequence below:

Once the system is restarted, the software checks the state of SFRBU_DDRBUMCR.BUMEN.
Restore all the context information.
Check that the Self-refresh status is OK (refer to the section Multiport DDR-SDRAM Controller (MPDDRC)).
Disable SFRBU_DDRBUMCR.BUMEN (see SFRBU DDR BU Mode Control Register).
The DDR memory exits Self-refresh mode when a memory access in the DDR memory space is performed.