Skyworks FEM control with 802.15.4 with NCS/Zephyr 2.0.0

Hi,

I'm having trouble getting the FEM in my Fanstel BT840X module working (the module with the nRF52840 processor and Skyworks 66112 amplifier).

I'm using nRF Connect version 2.0.0, though I can upgrade if it helps.

The first issue I've had is conflicting documentation on how to do this. I found that the recommended path of adding CONFIG_MPSL and CONFIG_MPSL_FEM does not build if you have CONFIG_NRF_802154_SOURCE_HAL_NORDIC in the project. I started this project from radio_test originally, and that sample uses the _NORDIC version.

The radio_test sample puts references to fem.c and generic_fem.c from the /nrf/samples/bluetooth/direct_test_mode/src/fem/ directory into CMakeLists.txt and Kconfig and it seems to expect you to use CONFIG_FEM and CONFIG_GENERIC_FEM in prj.conf. That scheme will at least build along with CONFIG_NRF_802154_SOURCE_HAL_NORDIC so I've been trying to use that.

Based on other support tickets I found, and information at this link,: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.9.0/nrf/ug_radio_fem.html#ug-radio-fem-skyworks

I modified my .dts file to add this code in the / { section:

nrf_radio_fem: skyworks_fem {
compatible = "skyworks,sky66112-11", "generic-fem-two-ctrl-pins";
ctx-gpios = <&gpio0 17 GPIO_ACTIVE_HIGH>;
crx-gpios = <&gpio0 19 GPIO_ACTIVE_HIGH>;
cps-gpios = <&gpio0 6 GPIO_ACTIVE_HIGH>;
chl-gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>;
};

and this code outside of that section: 

&radio {
fem = <&nrf_radio_fem>;
};

For my testing, I turned down the transmit power to -20dBm, and with the amplifier off my two boards can see each other at about -59dBm across my desk. At this level my boards can communicate but I'd definitely see a jump in RSSI if the amplifier were working.

If I put in the modified .dts file, my two devices can no longer talk to each other - regardless of the presence or absence of any CONFIG values in the prj.conf. So it seems like the .dts changes are making a difference, but not in the direction I expected.

Please help! This is urgent!

Thanks,

Glen

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  • Hi,

    Can you try setting cps-gpios to GPIO_ACTIVE_LOW? According to the SKY66112-11 datasheet, setting CPS high will put the FEM in "Receive/Transmit bypass mode", which will give you approximately -2 dB gain.

    Best regards,
    Jørgen

  • Didn't seem to make any difference. I decided to take the CPS and CHL out of the devicetree file and just configure them directly in firmware since they don't change anyway. So I'm just configuring the GPIO for CPS to always be 0 and for CHL to always be 1.

    I'm trying to dig into the generic FEM code to understand how it works.

    Is there a way to get an interrupt/callback function to fire just before and after any transmits (including 802.15.4 acknowledgements) where I could just manually control the pins and not have to fight with all this nonsense?

    Thanks,

    Glen

Reply
  • Didn't seem to make any difference. I decided to take the CPS and CHL out of the devicetree file and just configure them directly in firmware since they don't change anyway. So I'm just configuring the GPIO for CPS to always be 0 and for CHL to always be 1.

    I'm trying to dig into the generic FEM code to understand how it works.

    Is there a way to get an interrupt/callback function to fire just before and after any transmits (including 802.15.4 acknowledgements) where I could just manually control the pins and not have to fight with all this nonsense?

    Thanks,

    Glen

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