RSSI on Fanstel module with FEM dropped after SDK upgrade

RE: RSSI on Fanstel module with FEM dropped after SDK upgrade

Glen M — Tue, 06 Jan 2026 16:23:46 GMT

I ended up digging down into the library to find the function where the "power" RSSI value is set and it looks like it's just a numerical difference (as opposed to a real signal level difference). The older version of the SDK did not account for the LNA gain in the reported number and the new version does in nrf_802154_trx_rssi_last_sample_get().

So I ended up just updating my dts file to tell it that there's no gain from the LNA because I want consistency of behavior:

nrf_radio_fem: skyFem {
compatible = "skyworks,sky66112-11", "generic-fem-two-ctrl-pins";
ctx-gpios = <&gpio0 17 GPIO_ACTIVE_HIGH>;
crx-gpios = <&gpio0 19 GPIO_ACTIVE_HIGH>;
ctx-settle-time-us = <23>;
crx-settle-time-us = <5>;
tx-gain-db = <22>;
rx-gain-db = <0>; /* The real gain is 11dB but this number is included in the reported RSSI value and it has not been in the past so including it now is a change we dont want */
};

RE: RSSI on Fanstel module with FEM dropped after SDK upgrade

Vidar Berg — Fri, 02 Jan 2026 10:03:18 GMT

Yes, your pin configuration appears to be correct. Ideally, it would be good if you could measure the CHL and CPS signals to confirm they are being driven to ‘1’ and ‘0’ respectively, but I realise the pads may be difficult to access. Alternatively, you could use the peripheral viewer in VS Code (or a similar tool) to read the GPIO configuration registers to confirm the setup, and also check the serial peripheral interfaces to ensure that none are configured to use the same pins.

RE: RSSI on Fanstel module with FEM dropped after SDK upgrade

Glen M — Tue, 30 Dec 2025 20:28:59 GMT

Yes I think I have those configured correctly with the following code that's called at powerup:

#define SKYWORKS_AMPLIFIER_CTX_PIN 17 // GPIO port 0
#define SKYWORKS_AMPLIFIER_CRX_PIN 19 // GPIO port 0
#define SKYWORKS_AMPLIFIER_CPS_PIN 6 // GPIO port 0
#define SKYWORKS_AMPLIFIER_CHL_PIN 8 // GPIO port 0

m_gpio_port_0 = (struct device *)(device_get_binding("GPIO_0"));
m_gpio_port_1 = (struct device *)(device_get_binding("GPIO_1"));

gpio_pin_configure(m_gpio_port_0, SKYWORKS_AMPLIFIER_CPS_PIN, GPIO_OUTPUT_INACTIVE); // GPIO_OUTPUT_INACTIVE Configures GPIO pin as output and initializes it to a logic 0.
gpio_pin_configure(m_gpio_port_0, SKYWORKS_AMPLIFIER_CHL_PIN, GPIO_OUTPUT_ACTIVE); // GPIO_OUTPUT_ACTIVE Configures GPIO pin as output and initializes it to a logic 1.

RE: RSSI on Fanstel module with FEM dropped after SDK upgrade

Vidar Berg — Tue, 30 Dec 2025 11:22:40 GMT

Hello Glen,

There are quite many changes between SDK v2.3.0 and v3.1.0, but I haven't seen anything that should affect the FEM control. Are the pins highlighted below configured by your application to enable the FEM and high output mode (see table 6: https://www.skyworksinc.com/-/media/SkyWorks/Documents/Products/2201-2300/SKY66112-11_203225P.pdf)

Best regards,

Vidar