nRF5340 simple GPIO FEM Compatibility (Skyworks 66407)

[neo_here]

Hi, 

We have a product based on the nRF5340 and have a Skyworks 66407 FEM which uses a simple 2 GPIO control scheme. 

We have a shield configuration which enables the relevant MPSL symbols needed for this setup. 

 

#define CONFIG_MPSL_FEM_ANY_SUPPORT 1
#define CONFIG_MPSL_FEM_GENERIC_TWO_CTRL_PINS_SUPPORT 1
#define CONFIG_MPSL_FEM_NCS_SUPPORTED_FEM_USED 1
#define CONFIG_MPSL_FEM_API_AVAILABLE 1
#define CONFIG_MPSL_FEM 1
#define CONFIG_MPSL_FEM_SIMPLE_GPIO 1
#define CONFIG_MPSL_FEM_DEVICE_CONFIG_254 1
#define CONFIG_MPSL_THREAD_COOP_PRIO 6
#define CONFIG_MPSL_WORK_STACK_SIZE 1024
#define CONFIG_MPSL_TIMESLOT_SESSION_COUNT 0
#define CONFIG_MPSL_LOW_PRIO_IRQN 26

We are using the nRFConnect SDK 2.6.1 for our usecase. 

We observed that the RSSIs are poorer when we use the SoftDevice controller and compare it to the Zephyr controller. This was observed using the nRFConnect App on Android/iOS. 

There is about a 20db difference between Zephyr and Nordic SoftDevice Controllers. 

Here are the power profiler images for both. 

1) SoftDevice Controller


2) Zephyr Controller



As we can see, the current spikes on the zephyr controller seem more consistent with peak currents compared to Nordic SoftDevice. 


We also observed that a comment on the MPSL KConfig says that the 

"# MPSL_FEM_GENERIC_TWO_CTRL_PINS is not supported on nRF53 yet"

https://github.com/nrfconnect/sdk-nrf/blob/v2.7.0/subsys/mpsl/fem/Kconfig#L59


We wanted to know if we're seeing the lower RSSI measured from the SoftDevice controller due to a compatibility issue. 

I saw that even nRF54 supports this fully and only the nRF53 does not? 

[Hung Bui]

Hi Chinmay, 

As far as I know the nRF53 should support  MPSL simple GPIO FEM module. I believe the comment you saw in the code was from very old SDK and we have forgotten to remove that. I will need to check internally to see if that comment should be removed. 

As you can find in the documentation here: https://docs.nordicsemi.com/bundle/ncs-2.7.0/page/nrf/device_guides/fem/fem_simple_gpio.html

The nRF53 should at least support Skywork SKY66112 (I assume it's not much different to yours 66407 ) 
Could you please follow what in the documentation and let us know the result ? Please pay attention that for nRF53 you need to have an overlay for the netcore as mentioned in the doc.