Size restriction of composition data status message

[Marius Heil]

Hi,

the mesh profile spec 4.2.1, for the composition data page 0 states: "The size of the state shall not exceed the maximum useful access payload size". The maximum payload size seems like it is 380 bytes according to section 3.7.3.

When I flash the light lightness example, it uses 9 SIG models for the first element. So I expect that it could use around 7 elements for all other elements (excluding configuration server and health server). That means there is a restriction of around 20 elements with a light lightness server in a node.

Is this a fixed restriction so that I cannot have more elements/models in my node or is it simply the amount that can be reported using the composition data page 0? However, I expect that most clients would have problems dealing with a node that does not report all elements and models using the composition data.

Marius

[Mttrinh]

Hi,

Yes, there is an upper limit on a number of elements and models that can be initialized on a node so as not to exceed the maximum possible size of the composition data status message. The limit depends on the number of elements and the number of model instances that are allocated at compile time. It can be different for different scenarios. The only top-level requirement is that the size of the resultant composition data status message must not exceed the maximum possible access message size. This requirement is checked here at compile-time:

https://github.com/NordicSemiconductor/nRF5-SDK-for-Mesh/blob/master/models/foundation/config/src/config_server.c#L127

[Marius Heil]

Thanks, a rather severe restriction, but ok :-)