How to have nRF21540 finally working for BLE

[Lukáš]

Hi, the nRF21540 FEM is out for quite a long time. However, there is still no direct support in NCS. Fortunately. some work has already been done. This PR introduces the FEM driver in MPSL. But for no obvious reason, it states "Work is underway to make the protocols shipped with nRF Connect SDK use FEM, but none of them currently have this feature.".

• Could you please propose some modifications to the existing FEM driver in MPSL to have it working with BLE? There is "depends on !BT" but when we remove that manually it still doesn't do anything when BLE radio is working (GPIO pins are not moving).
• Could existing PA & LNA implementation of Zephyr controller work with nRF21540 in GPIO mode? Let's consider we will set is as following (using our GPIO mapping):

  CONFIG_BT_CTLR_GPIO_LNA=y
  CONFIG_BT_CTLR_GPIO_PA=y
  CONFIG_BT_CTLR_GPIO_LNA_PIN=3
  CONFIG_BT_CTLR_GPIO_LNA_OFFSET=11
  CONFIG_BT_CTLR_GPIO_PA_PIN=2
  CONFIG_BT_CTLR_GPIO_PA_OFFSET=11

Thanks

[Carl Richard]

Hi, Lukáš!

I will check internally if there are any easy way to enabled the FEM driver for BLE. I believe the reason that this is not prioritized is due to the regurlatory limits on transmission power that limits BLE devices to 10dBm in Europe, but I suggest talking with your RSM on further roadmap details regarding official support for the nRF21540. Our other chips are limited to 8dBm, which is usually sufficient.

I don't see why the GPIO mode won't work, but I will ask about that aswell.

There may be some time before I get answers, as we are approaching the holidays here. Thank you for the patience!

Best regards,
Carl Richard

[Lukáš]

Hey Richard,

Carl Richard said:

due to the regurlatory limits on transmission power that limits BLE devices to 10dBm in Europe,

Yeah, sure. But 1) some Nordic's chips don't even support the 8dBm, 2) those who do might want to compensate RF path loss so the PA is handy, 3) even the improved sensitivity using LNA is useful.

Carl Richard said:

I suggest talking with your RSM on further roadmap details regarding official support for the nRF21540.

Sure, we are in touch with our RSM. But with the particular development features, we are being forwarded to DevZone.

So the question is. What is the rationale for implementing FEM driver without BLE support? And why do you expect that users will want to enable some MPSL thing when they don't want to use any of its features?

Carl Richard said:

I don't see why the GPIO mode won't work, but I will ask about that aswell.

I also have good news! It seems that the kconfig options above work for nRF21540 using Zephyr Controller. At least the RX/TX path is switching. Of course, we are unable to drive other pins or set the TX gain.

[Carl Richard]

Hi again, Lukáš!

You're presenting good points. Though, I cannot comment on the rationale behind this. Hopefully your RSM can enlighten you on that matter, but I'll ask the developers as well.

Anyway, good to hear that you it does work! When asking internally about this I got back that it won't work out of the box as the nRF21540 timing is completely different from the Skywork's and you need to add additional signals. That said, all the doc needed to add this functionality is available in the PS.

I'm still awaiting answers when it comes to enabling the FEM driver with BT-functionality.

PS: The Holiday season is upon us, which will leave the Nordic support team understaffed until January 4th, 2021. This means that delayed replies will occur during this time. Sorry about the inconvenience and happy Holidays!

Best regards,
Carl Richard

[Lukáš]

Carl Richard said:

The Holiday season is upon us, which will leave the Nordic support team understaffed until January 4th, 2021. This means that delayed replies will occur during this time. Sorry about the inconvenience and happy Holidays!

Sure, that's understandable! Have a great Holiday.

[Lukáš]

Carl, I just got a call from our RSM and I think everything has been clarified. So I'm closing this one.