LoRaWAN: how to limit TX power?

[tve]

I'm using an stm32wle5 and need to limit the TX power to 10dBm due to battery constraints, what is the best way to achieve that? Calling node.setTxPower(10) doesn't affect OTAA as far as I can tell. I believe I need to set node.txPowerMax which is protected. Thoughts?

[StevenCellist]

There is no clean way of handling this within the LoRaWAN stack. The cleanest way I can think of is restricting the module driver to 10dBm max (here would be the right place I think).
By the way, out of curiosity, are you running through STM32duino or through STCube?

[HeadBoffin]

And adjust the ADR processing so that it doesn't get hijacked - or turn it off.

[StevenCellist]

Actually, that isn't even necessary at all - the ADR specification requires that a node is able to "operate at or below" the requested Tx power. As such the stack only sets the highest possible value out of (LoRaWAN, module), which might mean the module is the limiting factor. But it perfectly falls within spec :)

[HeadBoffin]

I meant that when an ADR request comes down the line, you'll need to restore the power settings - as the algorithm sets max power until it gets to SF7 then it start telling it reduce power if link budget allows.

[StevenCellist]

That is true for the case where you just use node.setTxPower(10), but if you modify the underlying module driver and limit its range to 10dBm, the stack will (should) never exceed this range.