nRF5 SDK for Mesh v4.1.0
Resource usage

To be functional, the mesh stack requires a minimum set of the hardware resources provided by the Nordic SoCs. The stack is designed to be built together with the user application and it resides in the application code space. Moreover, it relies on the SoftDevice being present and thus requires the same hardware resources as the SoftDevice.

For information on SoftDevice hardware resource requirements, see the relevant SoftDevice Specification.

Table of contents

SoftDevice Radio Timeslot API

The mesh stack operates concurrently with the SoftDevice through the SoftDevice Radio Timeslot API. Because the mesh stack takes complete control over the Radio Timeslot API, this API is unavailable to the application.

Hardware peripherals

The following hardware peripherals are occupied by the mesh stack:

RAM and flash usage

Depending on the application needs, the core mesh can be configured to achieve either higher performance and functionality or a reduced footprint.

When it comes to memory, the mesh stack:

See the Mesh memory manager interface for more details on how to replace the memory manager backend.

The following tables show the flash and RAM requirements for the mesh examples. The values are valid for all fully compatible configurations based on the nRF52 Series Development Kits.

The examples are built with the minimum recommended version of GNU Arm Embedded Toolchain.

Build type: MinSizeRel (-Os), Logging: On (default)

Flash usage (kB) RAM usage (kB) Example
95.952 11.712 Beaconing
98.600 11.992 DFU without serial interface
108.664 15.112 DFU with serial interface
111.360 13.008 Dimming client
115.432 13.156 Dimming server
112.608 13.400 EnOcean switch translator client
114.416 13.032 Light CTL client
149.932 17.264 Light CTL+LC server
136.088 15.648 Light CTL server
138.652 16.076 Light LC server
113.988 12.996 Light Lightness client
124.808 14.468 Light Lightness server
109.808 12.976 Light switch client
123.536 17.052 Light switch server
123.836 13.308 Low Power node
103.528 11.112 PB-remote client
99.532 11.540 PB-remote server
109.064 12.440 Provisioner
97.052 14.448 Serial

Build type: MinSizeRel (-Os), Logging: None

Flash usage (kB) RAM usage (kB) Example
82.844 9.448 Beaconing
83.348 9.728 DFU without serial interface
92.740 12.848 DFU with serial interface
93.624 12.992 Dimming client
98.256 13.140 Dimming server
94.680 13.384 EnOcean switch translator client
94.888 13.016 Light CTL client
124.484 17.248 Light CTL+LC server
114.784 15.632 Light CTL server
116.308 16.060 Light LC server
94.716 12.980 Light Lightness client
106.544 14.452 Light Lightness server
93.320 12.960 Light switch client
103.528 17.036 Light switch server
108.164 13.292 Low Power node
83.252 11.096 PB-remote client
83.488 9.276 PB-remote server
86.992 12.424 Provisioner
84.264 12.184 Serial

Flash hardware lifetime

The flash hardware can withstand a limited number of write and erase cycles. As the mesh stack uses the flash to store state across power failures, the device flash will eventually start failing, resulting in unexpected behavior in the mesh stack.

To improve flash lifetime, flash manager does wear leveling by writing a new data to the flash page by allocating a new entry and then invalidating the old one. Eventually, flash page fills up and must be erased and re-written (see flash manager documentation).

The mesh stack uses flash to store the following states:

Based on the assumption that the reconfiguration of keys, addresses, and access configuration is rare, the most likely source of flash write exhaustion are the network states. The network message sequence number is written to flash continuously, in user-configurable blocks.

Calculating flash lifetime

The following table lists parameters that must be defined to calculate the flash lifetime of a device.

Name Description and Configuration parameter Default nRF51 Series Default nRF52 Series Unit
MSG_PER_SEC The number of messages created by the device every second (relayed messages not included). The message sequence number field is 24 bits. It cannot be depleted within one IV update period, which must be at least 192 hours. Because of this, a device cannot possibly send more than 2^24 / (192 * 60 * 60) = 24.3 messages per second on average without breaking the specification.

Configuration parameter: N/A
24.3 24.3 messages/s
BLOCK_SIZE The message sequence numbers are allocated in blocks. Every block represents a set number of messages.

Configuration parameter: NETWORK_SEQNUM_FLASH_BLOCK_SIZE
8192 8192 messages
ENTRY_SIZE The size of a single allocated block entry in flash storage.

Configuration parameter: N/A
8 8 bytes
AREA_SIZE Size of the storage area. Must be in flash-page-size increments. Defaults to a single page.

Configuration parameter: N/A
1024 4096 bytes
AREA_OVERHEAD Static overhead in the storage area, per page.

Configuration parameter: N/A
8 8 bytes
ERASE_CYCLES The number of times the device can erase a flash page before it starts faulting.

Configuration parameter: N/A
20000 10000 cycles

The formula for the network state flash exhaustion is as follows:


Flash example values

SoC Settings Case Result
nRF51 Default Worst case 26.97 years
nRF52 Default Worst case 54.58 years

As any changes made to the default flash configuration may significantly reduce the product lifetime, recalculate the network state flash exhaustion time if any of the parameters change.

Flash configuration parameters

While the default settings will be sufficient for most applications, there are tradeoffs in the flash configuration that you might want to take advantage of.

Sequence number block size

The sequence number block size affects the number of power resets that the device can do within a 192-hour IV update period.

For security reasons, the device can never send a message with the same sequence number twice within an IV update period. This means that the device must allocate a new block of sequence numbers before it sends its first packet after a power reset, to avoid a scenario where it reuses the same sequence number on next powerup. As a consequence, every power reset requires a sequence number block allocation, which can exhaust the sequence number space faster than accounted for in the lifetime calculations.

With the default block size of 8192, the device may reset 2048 times in a 192-hour interval. If you expect a higher rate of resets, consider a smaller block size. Keep in mind that this will directly affect the flash lifetime, because more frequent writes are required during the normal operation.

The block size can also be increased if the number of power resets is expected to be lower than 2048, resulting in longer device lifetime.

Flash area size

The flash area size affects the number of erases required for the configuration and network state areas.

This does not alter the device lifetime significantly, because the flash manager defragmentation process requires a separate backup page that will be erased for every backed-up page. Adding pages to the flash area will therefore result in fewer, but more expensive defragmentations, with effectively no change to the number of erases required.

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