Flash

The flash is split into erasable pages of 8 kB. The various sections of flash and their associate linker files are as follows.

  • Flash Reset Vector Table: This table holds the first 16 reset vectors that are critical for booting up the device. These vectors are set at build time and cannot be dynamically changed.

  • Non-volatile (NV) Area: used for nonvolatile memory storage by the Zigbee network information and also available for use by the application. See Non-Volatile Memory Items for configuring NV.

  • Application and Stack Image Code Space: A single region that contains both application and stack code in flash. This image is configured in the linker configuration file of the application: <device name>_app.cmd (CCS).

Non-Volatile Storage Architecture

This section will describe the non volatile storage system that is implemented and used on the CC23xx. This system provides access to non volatile storage that can be safely shared between the user application and the protocol stack.

The system has the following properties and offers the following features:

  • Thread safe access to non volatile memory

  • ID based system that decouples a storage item from its address in memory

  • Space efficient storage with automatic compaction

  • Power loss tolerant data preservation

The implementation of this software system relies on several layers which are illustrated below.

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Non Volatile RAM (NVRAM)

The NVRAM is an abstraction layer that defines a common set of APIs for interacting with non volatile memory using ZBOSS. This common set of APIs allow for new methods of NV storage to be implemented without changing the API calls in the stack and application, as seen in ti_f3_nvram.c. For more information, please consult the ZBOSS User’s Guide.

Non Volatile Storage (NVS) Driver

The NVS driver provides reentrant functions for writing to and reading from flash. It also provides a common interface to both internal and external flash. More information can be found in the TI Drivers documentation. The stack will use internal NV, currently this is all that is supported.

Non-Volatile Memory Items

Global Configuration Non-Volatile Memory

This feature is enabled by default by the inclusion of the ZB_USE_NVRAM compile option. Note that this feature must be always enabled in a real Zigbee network. The ability to disable it is only intended for use in the development stage.

A Zigbee device has lots of state information that needs to be stored in non-volatile memory so that it can be recovered in case of an accidental reset or power loss. Otherwise, it will not be able to rejoin the network or function effectively. This includes items such as PAN ID, key information, network settings, etc. These items are loaded to RAM at startup for quick access during Zigbee 3.0 operation. To initialize the non-volatile memory area to store these items, ensure that the zb_set_nvram_erase_at_start function in MAIN has a parameter of ZB_FALSE (this is the default for sample applications). Other useful APIs can be found in zboss_api.h and further detailed within the ZBOSS User’s Guide.

Application Non-Volatile Memory

In general, a device must have non-volatile memory enabled to be certified, because it must remember its network configuration. In addition to the stack ‘internal’ data, the NVM can also be used to store application data.

Modifying Non-Volatile Memory Allocation

By default, Zigbee 3.0 projects allocate flash pages for non-volatile (NV) memory with Region Base and Region Size settings in the project’s .syscfg file TI Drivers → NVS → Internal Flash. The command linker (.cmd) file accounts for changes automatically.

The amount of required NV memory greatly depends on the definitions provided in the table below. Total NV allocation required for a Zigbee 3.0 project can be estimated by multiplying the bytes per entry by the value of the definition then adding them all together along with ~2.3 kB for remaining NV items which aren’t as liable to fluctuate depending on network settings. See the Zigbee stack flash usage configuration section of the ZBOSS User’s Guide for more details.