802.15.4 Stack with FEM Control

[eboris]

We have an application for using the 802.15.4 protocol with a nRf52840 and a Front End Module. We are looking for an approach to take for integrating the FEM control into the firmware.

First I wanted to ask: Could you recommend an approach on how we could solve the problem of integrating the FEM control with the 802.15.4?

The possibilities that we came up with are:

1) Use the SDK 15.3 with the S140 soft device. Use the API sd_ble_opt_set() with a configured configuration structure and the soft device should take control of the FEM. Would the soft device then automatically control the FEM?

2) Use the SDK 15.3 with the S140 soft device. Then use a PPI event from when radio turns ON to Tx to initiate an action on a GPIO pin that would turn the PA of the FEM. Likewise an Rx event would create a PPI event to initiate and action on another GPIO pin that would turn the LNA ON. 

3) Use the 802.15.4 stack in Zephyr. Modify the Zephyr stack to add the FEM control. 

Any thoughts or recommendations that you can provide would be helpful.

Note: This is a continuation of https://devzone.nordicsemi.com/f/nordic-q-a/52822/fem---front-end-module-management.

[bjorn-spockeli]

Hi Eboris, 

I sincerly apologize for the late reply. I have been out of office. 

1) Use the SDK 15.3 with the S140 soft device. Use the API sd_ble_opt_set() with a configured configuration structure and the soft device should take control of the FEM. Would the soft device then automatically control the FEM?

Our SoftDevices only support Bluetooth Low Energy, so configuring the SD to use a FEM using sd_ble_opt_set() will only affect BLE. When running BLE concurrently with a 802.15.4-based protocol, then the 802.15.4 stack will be running in a SoftDevice Timeslot, i.e. a timeslot inbetween the BLE events. The RADIO peripheral is then reconfigured by the 802.15.4 stack and then when the timeslot ends the SoftDevice configures it back to the settings it uses. 

2) Use the SDK 15.3 with the S140 soft device. Then use a PPI event from when radio turns ON to Tx to initiate an action on a GPIO pin that would turn the PA of the FEM. Likewise an Rx event would create a PPI event to initiate and action on another GPIO pin that would turn the LNA ON.

Yes, this might be a doable solution, you could for instance use the EVENTS_TXREADY and EVENTS_RXREADY events to turn on the PA/LNA of the FEM,

3) Use the 802.15.4 stack in Zephyr. Modify the Zephyr stack to add the FEM control. 

I guess this also might be a viable solution, but I have not worked with the 802.15.4 stack in Zephyr so I do not know how much effort this will be. 

Best regards

Bjørn