Zigbee stack flash usage configuration

Table of Contents

• Amount of memory used
• Adjusting persistent data area

Every Zigbee device uses a part of the internal flash memory to store data, which allows to restore its functionality after power cut.

The following data is stored inside the flash memory:

• Device configuration:
  • stack profile
  • list of allowed channels
  • security settings
• Current network data:
  • addresses of the network manager, Trust Center, and parent
  • network channel, PAN ID, assigned short address
  • network key, TC link key, install codes
  • neighbor table
  • EUI64 address resolution table
  • poll control intervals and timeout values
• Device diagnostic data:
  • number of resets
  • number of join attempts
  • number of buffer allocation errors
• Common application settings:
  • local binding table entries
  • binding table
  • group membership of every active endpoint
  • attribute reporting configuration
  • Green Power Proxy Basic (GPPB) data
• Cluster specific settings

Amount of memory used

The memory reserved for storing the data is divided into two virtual pages of the same size. By default, the size of both pages is set to 16 kB to address the needs of more demanding Zigbee applications.

The amount of data that is written by the Zigbee device depends on its role inside the network and the complexity of the application. All stored values are organized into datasets that can be updated. This organization affects the flash usage, because if a certain value changes, the whole dataset that contains its value must be updated. The following table contains the list of the defined datasets, their sizes, and the device types for which these datasets are relevant.

Dataset size [bytes]	Dataset name	Device type
20	NVRAM page header.	All devices.
96	Common dataset (device configuration, network data).	All devices.
24	Counters (NIB, AIB versions).	All devices.
20 + 16 * ZB_CONFIG_IEEE_ADDR_TABLE_SIZE	EUI64 address map.	All devices.
20 + 4 * ZB_CONFIG_NEIGHBOR_TABLE_SIZE	Neighbor table.	All devices.
20 + 28 * ZB_CONFIG_N_APS_KEY_PAIR_ARR_MAX_SIZE	APS link keys (e.g. TC link key).	All devices.
20 + 28 * n_install_codes	Install codes.	All devices.
54	GPPB cluster data.	Coordinator and routers.
248	GPPB proxy table.	Coordinator and routers.
40	HA dataset (poll control, diagnostic data).	Application-specific.
116	APS group table.	Application-specific.
16 + 24 * n_report_info	Attribute reporting configuration.	Application-specific.
16 + binding_table_size	Local binding table.	Application-specific.

Defined dataset sizes and device types

Note

• The n_install_codes variable must be equal to OVERALL_NETWORK_SIZE for the coordinator node and to 2 for other devices.
• The value of n_report_info must be equal to the amount of reportable attributes in your application (see cluster description in the ZCL specification).
• Use the following formulas to calculate binding_table_size:
  • For end devices: 116 + ZB_APS_BIND_TRANS_TABLE_SIZE + 16 * ((ZB_APS_BIND_TRANS_TABLE_SIZE + 7)/8)
  • For coordinator and routers: 212 + ZB_APS_BIND_TRANS_TABLE_SIZE + 32 * ((ZB_APS_BIND_TRANS_TABLE_SIZE + 7)/8)

The following table shows the estimates for the minimum value of flash memory that is written for a Zigbee device. It assumes that the network consists of two nodes.

ZC/ZR Dataset size [bytes]	ZED Dataset size [bytes]	Dataset name	Note
20	20	NVRAM page header.	Every virtual page starts with a header.
96	96	Common dataset (device configuration, network data).	-
24	24	Counters (NIB, AIB versions).	-
20 + 16	20 + 16	EUI64 address map.	At least one for the parent device.
20 + 4	20 + 4	Neighbor table.	At least one for the parent device.
20 + 56	20 + 56	APS link keys (e.g. TC link key).	At least two - provisional and verified.
20 + 28	20 + 28	Install codes.	If the device uses install codes for commissioning (recommended).
54	-	GPPB cluster data.	Mandatory for the coordinator and routers.
248	-	GPPB proxy table.	Mandatory for the coordinator and routers.
40	40	HA dataset (poll control, diagnostic data).	Application-specific.
116	116	APS group table.	Application allows to use APS groups.
16 + 0	16 + 0	Attribute reporting configuration.	Application does not have reportable attributes.
252	140	Local binding table.	Low traffic, low complexity.
Total: 1050 bytes	Total: 636 bytes	-	-

Flash memory minimum value estimates

To estimate the required amount of flash memory, you can use the value calculated above as the base. Add more entries of the application-specific datasets and, depending on your application:

• on the coordinator node: at least 76 bytes for every additional node in the network,
• on router nodes: at least 20 bytes for every additional node in the network.

Note

• If the current virtual flash page is filled up with data, every valid dataset must be rewritten into a second page. Because of this, the minimal virtual page size must be greater than the amount of stored data multiplied by 4.
• Recommended: Use larger virtual pages than calculated for a particular network to reduce the amount of flash erase cycles and extend the device lifetime.

Adjusting persistent data area

You can change size of the persistent data area by modifying ZIGBEE_NVRAM_PAGE_SIZE and ZIGBEE_NVRAM_PAGE_COUNT configuration options in the SDK configuration header file.

The persistent data is stored close to the end of flash memory, as described in Zigbee stack memory layout.