SDK backwards compatibility support for older SD

[tlgage]

I was looking at this compatibility matrix, for SD and SDK. 

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcomp_matrix_nrf52832%2FCOMP%2Fnrf52832%2Fic_rev_sdk_sd_comp_matrix.html

Are SDKs meant to be backwards compatible with all older versions of SDs? Or is this not recommended? It seems like the answer is no, which would be fine to get confirmation. 

To provide context, if I have a device in the field running SDK v14.2, SD132 v5.1 and I want to upgrade my SDK, but I am not able to upgrade my SD132 and keep it at v5.1.0 is that ok to do? So I would try and use SDK v15.0 (next version up) with SD132 v5.1.0. Would like confirmation that is a bad idea before I go down the route of exploring trying to do that. 

[ovrebekk]

Hi 

Minor SoftDevice updates (S132 v5.0.0 to v5.1.0 for example) will never change existing API's, they will only modify the implementation of existing ones or add new ones. 

This means that you can safely update to a new minor version without changing the SDK. 

Major SoftDevice updates on the other hand (S132 v5.x.x to v6.x.x for example) can both change and remove existing API functions, in addition to adding new ones, and they will normally not work on other SDK versions than the ones they were designed for. 

This means you normally need to change both the SoftDevice and SDK version if you plan to upgrade to a new major version of the SoftDevice. 

Best regards
Torbjørn

[tlgage]

Makes sense, thanks!

[ovrebekk]

You welcome