Using SHCI_C2_BLE_INIT_OPTIONS_REDUC_GATTDB_NVM to increase bonding list size

[DS.4]

Wondering what is the cost of using 

SHCI_C2_BLE_INIT_OPTIONS_REDUC_GATTDB_NVM

over

SHCI_C2_BLE_INIT_OPTIONS_FULL_GATTDB_NVM

?

 

The first one can gets me 33% increase in bonding list size but I could not find what does it prevent me from using?

[STTwo-32]

Hello @DS.4 

The REDUC_GATTDB_NVM can be used in all the cases.

When using the FULL_GATTDB_NVM and SVC_CHANGE_DESC, the GATT database record in NVM is composed as describe in the wiki page by:

• Per service:
  • 2 bytes for handle
  • 3 bytes if 16-bit UUID or 17 bytes if 128-bit UUID

• Per characteristic attribute:
  • 2 bytes for handle
  • 3 bytes if 16-bit UUID or 17 bytes if 128-bit UUID
  • 2 bytes for CCCD value (only if the attribute is a CCCD)

When using the REDUC_GATTDB_NVM and SVC_CHANGE_DESC, the GATT database record in NVM is composed by:

• Per characteristic attribute:
  
  • 3 bytes for CCCD value (only if the attribute is a CCCD)
    + 16 bytes (The Data Base hash stores a 128 bits value calculated from the Data Base structure. Any change in the Data Base structure results in a different hash value.)

When a connection is established with a previously bonded device, the GATT database is compared with the GATT database saved in NVM. If there is a difference between the databases, a service change indication will be sent to the peer device. The contents of the indication will depend of FULL_GATTDB_NVM and REDUC_GATTDB_NVM flags:

- When using FULL_GATTDB_NVM, you know where the change is located, the service change indication will contain the specific handle of the service/characteristic where there is the modification.
- When using REDUC_GATTDB_NVM, since the data stored in NVM is a hash, it is not possible to know where is located the change, the service change indication will indicate a change of all the database.

 

More details are available on this WiKi.

Best Regards.

STTwo-32

[DS.4]

"When using FULL_GATTDB_NVM, you know where the change is located, the service change indication will contain the specific handle of the service/characteristic where there is the modification.
- When using REDUC_GATTDB_NVM, since the data stored in NVM is a hash, it is not possible to know where is located the change, the service change indication will indicate a change of all the database."

Perfect thanks!