RCP: How to set Radio transmit power as channel changes?

[rretanubun]

Hello,

My platform is a TME built on an RCP architecture on Thread stack 1.3.0

My RCP stack have support for otPlatRadioGetTransmitPower() and otPlatRadioSetTransmitPower()
and I can see the spinel messages being sent to the RCP.

otPlatRadioSetChannelMaxTransmitPower() is returning NotImplemented
because it maps to the weak function in /src/code/radio/radio_platform.cpp

As I understand it, the RCP vendor library also does not support pre-mapping Channel to TransmitPower
and expect to be told the transmit power to use for the channel in use.

In some regions of the world (e.g. North America) the allowed transmit power
is different per channel (for example Ch-11-to-25 = 19 dBm and Ch-26 = 9.9 dBm)
So it seems each time the device switches channels, it needs to check what channel it is switching to
and call otPlatRadioSetTransmitPower() accordingly.

Outside of just intentional operational dataset changes, Thread have other mechanisms
that causes it to switch channels (e.g. MLE Announcements)

Is there a good place to hook in the call to SetTransmitPower to the RCP Radio
(e.g. https://github.com/openthread/openthread/blob/main/src/lib/spinel/radio_spinel_impl.hpp#L2020)
to handle such cases (or is this handled already using a different mechanism?)

Thank you for everyone's time.

[jwhui]

Ideally, the radio vendor should provide drivers that implement the appropriate radio platform APIs, like otPlatRadioSetChannelMaxTransmitPower. This is what they are designed for. I would reach out to the radio vendor regarding implementation of these radio platform APIs.

[rretanubun]

Thanks Jonathan, I am following up on the vendor side as well. The piece that is not clear to me
is the expected behavior that Thread needs the Radio platform APIs to perform.

For example, is the expectation otPlatRadioSetChannelMaxTransmitPower is called for channel 11-26 once at boot from the host-processor to the RCP and then as channels are used, the RCP will automatically apply the pre-configured TransmitPower?

Or is the host processor going to send otPlatRadioSetChannelMaxTransmitPower each time a channel is switched and the RCP just applies the latest settings?

I am not clear which entity (Host vs RCP) is expected to host the channel to Transmit power map during run time in this design.

[jwhui]

The radio driver should maintain this map. You can refer to the nRF528xx implementation as one example.