How to specify default TX power at runtime for the nrf5340?

[EDLT]

I know how to set the TX power on an individual bluetooth handle basis per connection/advertisement. This is fine for advertising because I can create the advertising set, set the power level, then start advertising. But for connections I don't see a way to specify the desired connection power level prior to creating the connection. It seems like I need to create the connection first, and then I can set the advertising power.

Alternatively, is there a way to tell the network core that all output power should be lowered by a specific amount as a default for all outgoing signals so that I don't have to specify the power level for each connection? I need this to be a run time change instead of a build time configuration.

Edit: Specifically I am hoping for an app-core side solution.

[Einar Thorsrud]

Hi,

You can use the approach shown in this post.

[EDLT]

Thanks, I understand the use of the HCI commands for setting the power on a per handle basis and use those. I was hoping for something like "sdc_default_tx_power_set" that can be triggered from the application core after the BLE stack is already initialized.

[Einar Thorsrud]

Hi,

Sorry, the link was wrong. I did not find the one I indended to link to again now, but it is essentially what is demonstrated in the HCI Power Control sample. This demonstragte how you adjust the Tx power on the host side (so the app core on he nRF53).

A key poin there, which is demonstrated by the sample but perhaps not very clearly, is that the Tx power used for advertising will be the initial (default if you like) Tx power for the resulting connection. So there is no need to explicitly set the Tx power for the connection(s) as long as you set it for the advertiser.

[EDLT]

I didn't realize the peripheral connection power level is determined from the advertising power level. That is a helpful bit of information.

I don't imagine this applies for the central role, who may know nothing about the peripheral's TX power level. For the central, how does one setup the connection power level before connecting?

[Einar Thorsrud]

Hi,

I did not get a chance to test this now, but looking at the implementation the same shoudl apply to scanning, by using handle type  BT_HCI_VS_LL_HANDLE_TYPE_SCAN.

[EDLT]

I see, since there's no handle, what handle value should be used when constructing bt_hci_cp_vs_write_tx_power_level?

[Einar Thorsrud]

The handle is ignored when the type is scan, so you can pass 0.

[EDLT]

Einar, thanks for your input. I was able to test and verify the behavior. I've not seen anything like this mentioned in documentation, and think it would be great to add this kind of detail. Thanks again for your help.