Transmit power control with Gazelle (gzll)

RE: Transmit power control with Gazelle (gzll)

ovrebekk — Thu, 14 Mar 2019 09:44:01 GMT

Hi Ray

Can't say I disagree 🙂

Next time you run into someone from Nordic sales mention it to them as well. At the end of the day requests for new features or improvements have to go through them ;)

Best regards
Torbjørn

RE: Transmit power control with Gazelle (gzll)

RayFoulkes — Wed, 13 Mar 2019 12:30:16 GMT

Hi Torbjørn, thanks for the response. I will write up my experience of using nrf_radio_txpower_set which has not been all plain sailing.

On the issue of documentation, my long-held view is that it is primarily a matter of training the software developers to think of the users. The developers KNOW how something is supposed to work so adding in a few comments in-line (as all the code documentation is inline) should be a few minutes work. It is useful to know the state of the system in which a call can be made and surely the developer knows that. An example of one developer who is trying to be helpful is whoever wrote nrf_dfu_trigger_usb_init which at least gives a few hints about how to use it. Unfortunately, there is a lot of code with much less helpful (or no) hints.

Just my thoughts, I know you cannot do anything about it! Keep smiling, Ray

RE: Transmit power control with Gazelle (gzll)

ovrebekk — Tue, 12 Mar 2019 08:13:08 GMT

Hi Ray

Sorry for the slow reply, I forgot to look over my verified cases...

Feel free to share any information here on your blog, if you haven't already. Since it is a public case it is already out there 🙂

Good find on the nrf_radio functions, should make things easier.

Regarding the documentation I agree it is slim on the interplay between different functions and libraries. Mainly this is a resource issue, as it takes a lot of time to write and maintain such documentation with all the changes there are to the various libraries and modules for every SDK update. For the foreseeable future I expect the examples will be the best reference for this ;)

Best regards
Torbjørn

RE: Transmit power control with Gazelle (gzll)

RayFoulkes — Fri, 25 Jan 2019 15:49:31 GMT

OOPs, I have just found that there are already functions (inline) in nrf_radio.h which sets and gets the power and this time it does include 8dbm (from nrf52840.h). These are:

__STATIC_INLINE void nrf_radio_txpower_set(nrf_radio_txpower_t tx_power)
{
NRF_RADIO->TXPOWER = (((uint32_t)tx_power) << RADIO_TXPOWER_TXPOWER_Pos);
}
and the equivalent "get".

So, all the work has been done for register writing.

Regards, Ray

RE: Transmit power control with Gazelle (gzll)

RayFoulkes — Fri, 25 Jan 2019 15:05:01 GMT

Wow, Torbjørn, thanks VERY much for such a clear response. I understand that library changes are not in your hands and I guess that gzll is not that high on the Nordic priority list.

I trust it is OK if I document this solution in my little blog since others might benefit - I don't think that there is anything particularly secret or sensitive about it.

I must admit that I struggle a bit with the SDK documentation. There are general guides (such as those for gzll link layer and pairing) which give an overview and the syntactic signature of data and subroutine invocations. Often the middle bit is missing i.e. the semantic part for the subroutine invocations such as preconditions, interdictions (when you can call and when you cannot) and postconditions (i.e. what state (if any) is the software left in after call. The examples go so far, but they are only examples so you have to try to deduce the semantics from examples - which I find hard.

Anyway, at least Nordic do their very best to help clarify individual cases and I thank you very much once again for that.

RE: Transmit power control with Gazelle (gzll)

ovrebekk — Fri, 25 Jan 2019 12:28:46 GMT

Hi Ray

The only time the Gazell library will set the TX power is during nrf_gzll_init(..), where it is assigned a default value, and any time you call nrf_gzll_set_tx_power(..).

In other words there is no dynamic change of TX power happening internally. This has to occur in the application (or in some other module using Gazell, like the GZP library).

Any time Gazell is initialized and idle you can safely call nrf_gzll_set_tx_power(..), but if you are in the process of transmitting something I would recommend against it.

To get around the limitation of the nrf_gzll_set_tx_power(..) function you can simply write to the TXPOWER register in the radio, that is correct. The same recommendation applies: Write to the register after initializing Gazell, before you start sending or receiving packets.

I can request the library to be updated with support for +8dBm, but can obviously not make any promises as to if or when it is fixed.

Best regards
Torbjørn