Coexistence of short-range radio and other radios

This guide describes how to add short-range radio and other radio coexistence support to your application in nRF Connect SDK.

Short-range RF technologies (here referred to as SR), such as Bluetooth LE or 802.15.4, use a different radio than other technologies like Wi-Fi or LTE (here referred to as the other radios). However, if both SR and the other radio attempt to transmit simultaneously, the radio frequency (RF) waves interfere with each other, causing decreased performance and higher power consumption. Also, in cases like receiving an acknowledgment (ACK), radios should not transmit to ensure correct reception.

These issues are defined as coexistence issues. To mitigate these issues and to improve performance, a Packet Traffic Arbiter (PTA) is used. When both SR and the other radio request access to RF, the Packet Traffic Arbiter grants or denies that access.

Integration considerations

The nRF Connect SDK provides the coexistence feature by providing SR protocol drivers that can call the coexistence API and its implementations. This feature is based on Short-Range Protocols External Radio Coexistence provided by the Multiprotocol Service Layer (MPSL) library.

The following SR protocols are compatible with the coexistence feature:

• Bluetooth LE, if the implementation used is the SoftDevice Controller.

• Protocols based on nRF 802.15.4 Radio Driver, such as Thread and Zigbee.

The following drivers are available:

• nRF70 Series Wi-Fi coexistence

• Generic three-wire coexistence

• Generic one-wire coexistence

• Custom coexistence implementations

The nRF Connect SDK provides a wrapper that configures Wi-Fi Coexistence based on devicetree source (DTS) and Kconfig information.

The following are the common requirements to use the coexistence feature:

1. The Kconfig option CONFIG_MPSL must be enabled. Some protocol drivers, like SoftDevice Controller, enable this option by default.

2. The Kconfig option CONFIG_MPSL_CX must be enabled.

3. The requirements specific to the selected coexistence implementation must be met. These include at least selecting one of supported values of the CONFIG_MPSL_CX_CHOICE choice. For details on the requirements specific to the selected coexistence implementation, consult its documentation.

4. Ensure that the configuration of the nrf_radio_coex node appropriate for the selected implementation is present in the devicetree. When using one of the supported implementations, you must use the nrf_radio_coex name for the node. However, if you add a custom user implementation, you can also use a different name. Some boards supported by the nRF Connect SDK (like nrf7002dk) provide this node by default. You can provide the node using either the devicetree source file of the target board or an overlay file. See Devicetree Guide for more information about the DTS data structure, and Devicetree versus Kconfig for information about differences between DTS and Kconfig.

5. On the nRF5340 SoC, the GPIO pins required for the communication with the PTA must be handed over to the network core. You can use the nrf-gpio-forwarder node in application’s core devicetree for that.

6. You can add a new device binding and use it as the compatible property for the node, if the provided hardware interfaces are unsuitable.

Note

When using the nRF5340, apply steps 1 and 2 only to the network core. See Multi-image builds using child and parent images.

Note

Do not enable Wi-Fi coexistence on the nRF5340 SoC in conjunction with Coded Phy and FEM, as this can lead to undefined behavior.

Supported implementations

The following are the SR protocol driver implementations supported by the nRF Connect SDK.

nRF70 Series Wi-Fi coexistence

The nRF70 Series Wi-Fi coexistence implementation is a three-wire coexistence interface compatible with nRF70 Series devices.

Hardware description

The nRF70 Series device interface consists of the signals listed in the table below. The Pin is the pin name of the nRF70 Series device. The Direction is from the point of view of the SoC running the SR protocol. The DT property is the name of the devicetree node property that configures the connection between the SoC running the SR protocol and the nRF70 Series device.

nRF70 Series device coexistence protocol pins

Pin	Direction	Description	DT property
COEX_REQ	Out	Request signal	req-gpios
COEX_STATUS0	Out	SR transaction direction TX or RX	status0-gpios
COEX_GRANT	In	Grant	grant-gpios

Enabling nRF70 Series Wi-Fi coexistence

To enable Wi-Fi coexistence on the nRF70 Series device, complete the following steps:

1. Add the following node to the devicetree source file:

   / {
         nrf_radio_coex: nrf7002-coex {
            status = "okay";
            compatible = "nordic,nrf700x-coex";
            req-gpios =     <&gpio0 24 (GPIO_ACTIVE_HIGH)>;
            status0-gpios = <&gpio0 14 (GPIO_ACTIVE_HIGH)>;
            grant-gpios =   <&gpio0 25 (GPIO_ACTIVE_HIGH | GPIO_PULL_UP)>;
      };
   };
   

2. Optionally, replace the node name nrf7002-coex with a custom one.

3. Replace the pin numbers provided for each of the required properties:

   • req-gpios - GPIO characteristic of the device that controls the COEX_REQ signal of the nRF70 Series device.

   • status0-gpios - GPIO characteristic of the device that controls the COEX_STATUS0 signal of the nRF70 Series device.

   • grant-gpios - GPIO characteristic of the device that controls the COEX_GRANT signal of the nRF70 Series device.

   Note

   GPIO_PULL_UP is added to avoid a floating input pin and is required on some boards only. If the target board is designed to avoid this signal being left floating, you can remove GPIO_PULL_UP to save power.

   The phandle-array type is used, as it is commonly used in Zephyr’s devicetree to describe GPIO signals. The first element &gpio0 indicates the GPIO port (port 0 has been selected in the example shown). The second element is the pin number on that port.

4. On the nRF5340, apply the same devicetree node mentioned in Step 1 to the network core. Apply the overlay to the correct network-core child image by creating an overlay file named child_image/*childImageName*.overlay in your application directory, for example child_image/multiprotocol_rpmsg.overlay.

   The *childImageName* string must assume one of the following values:

   • multiprotocol_rpmsg for multiprotocol applications having support for both 802.15.4 and Bluetooth.

   • 802154_rpmsg for applications having support for 802.15.4, but not for Bluetooth.

   • hci_ipc for application having support for Bluetooth, but not for 802.15.4.

5. Enable the following Kconfig options:

   • CONFIG_MPSL_CX

   • CONFIG_MPSL_CX_NRF700X

   Note

   If a nordic,nrf700x-coex compatible node is present in the devicetree and CONFIG_MPSL_CX is set to y, MPSL_CX_NRF700X will be selected by default.

Generic three-wire coexistence

The generic three-wire coexistence is a three-wire coexistence interface which follows the Thread Radio Coexistence Practical recommendations for using a three-wire PTA implementation for co-located 2.4 GHz radios.

Hardware description

The generic three-wire interface consists of the signals listed in the table below. The Pin is a generic pin name of a PTA, identified rather by its function. The Direction is from the point of view of the SoC running the SR protocol. The DT property is the name of the devicetree node property that configures the connection between the SoC running the SR protocol and the Wi-Fi device.

Generic three-wire coexistence protocol pins

Pin	Direction	Description	DT property
REQUEST	Out	Request signal	req-gpios
PRIORITY	Out	Priority signal	pri-dir-gpios
GRANT	In	Grant signal	grant-gpios

Enabling generic three-wire coexistence

To enable the generic three-wire coexistence, do the following:

1. Add the following node to the devicetree source file:

   / {
         nrf_radio_coex: radio_coex_three_wire {
            status = "okay";
            compatible = "generic-radio-coex-three-wire";
            req-gpios =     <&gpio0 24 (GPIO_ACTIVE_HIGH)>;
            pri-dir-gpios = <&gpio0 14 (GPIO_ACTIVE_HIGH)>;
            grant-gpios =   <&gpio0 25 (GPIO_ACTIVE_HIGH | GPIO_PULL_UP)>;
      };
   };
   

2. Optionally, replace the node name radio_coex_three_wire with a custom one.

3. Replace the pin numbers provided for each of the required properties:

   • req-gpios - GPIO characteristic of the device that controls the REQUEST signal of the PTA.

   • pri-dir-gpios - GPIO characteristic of the device that controls the PRIORITY signal of the PTA.

   • grant-gpios - GPIO characteristic of the device that controls the GRANT signal of the PTA (RF medium access granted).

     Note

     GPIO_PULL_UP is added to avoid a floating input pin and is required on some boards only. If the target board is designed to avoid this signal being left floating, you can remove GPIO_PULL_UP to save power.

   The phandle-array type is used, as it is commonly used in Zephyr’s devicetree to describe GPIO signals. The first element &gpio0 indicates the GPIO port (port 0 has been selected in the example shown). The second element is the pin number on that port.

4. On the nRF5340, apply the same devicetree node mentioned in Step 1 to the network core. Apply the overlay to the correct network-core child image by creating an overlay file named child_image/*childImageName*.overlay in your application directory, for example child_image/multiprotocol_rpmsg.overlay.

   The *childImageName* string must assume one of the following values:

   • multiprotocol_rpmsg for multiprotocol applications having support for both 802.15.4 and Bluetooth.

   • 802154_rpmsg for applications having support for 802.15.4, but not for Bluetooth.

   • hci_ipc for application having support for Bluetooth, but not for 802.15.4.

5. Enable the following Kconfig options:

   • CONFIG_MPSL_CX

   • CONFIG_MPSL_CX_3WIRE

Generic one-wire coexistence

An example use-case of the generic one-wire coexistence interface is to allow a protocol implementation to coexist alongside an LTE device on a separate chip, such as the nRF91 Series SiP.

Hardware description

The generic one-wire interface consists of the signals listed in the table below. The Pin is a generic pin name of a PTA, identified rather by its function. The Direction is from the point of view of the SoC running the coexistence protocol. The DT property is the name of the devicetree node property that configures the connection between the SoC running the coexistence protocol and the other device.

Generic one-wire coexistence protocol pins

Pin	Direction	Description	DT property
GRANT	In	Grant signal	grant-gpios

In cases where the GPIO is asserted after the radio activity has begun, the GRANT signal triggers a software interrupt, which in turn disables the radio. No guarantee is made on the latency of this interrupt, but the ISR priority is configurable.

Note

The Multiprotocol Service Layer (MPSL) library uses interrupts with priority 0. This may delay the GPIOTE interrupt in some rare cases. For that reason, it’s recommended to deny SR radio activity at least 400 microseconds before activity on the other radio, and to use a GPIOTE interrupt priority as close to 0 as possible.

Enabling generic one-wire coexistence

To enable the generic one-wire coexistence, do the following:

1. Add the following node to the devicetree source file:

   / {
         nrf_radio_coex: radio_coex_one_wire {
            status = "okay";
            compatible = "generic-radio-coex-one-wire";
            grant-gpios =   <&gpio0 25 GPIO_ACTIVE_LOW>;
            concurrency-mode = <0>;
      };
   };
   

   The concurrency-mode property is optional and can be removed. By default, or when set to 0, the GRANT signal will prevent both TX and RX. When set to 1, it will only prevent TX.

2. Optionally, if not using the nRF91 Series SiP, the GRANT signal may be configured active-high using GPIO_ACTIVE_HIGH

3. Optionally, replace the node name radio_coex_one_wire with a custom one.

4. If not already present in the device tree, the GPIOTE interrupt may additionally be configured as follows (the first element is the IRQn, and the second is the priority):

   &gpiote {
     interrupts = < 6 1 >;
   };
   

5. Replace the pin number provided for the grant-gpios property: This is the GPIO characteristic of the device that interfaces with the GRANT signal of the PTA (RF medium access granted).

   The first element &gpio0 indicates the GPIO port (port 0 has been selected in the example shown). The second element is the pin number on that port.

6. Enable the following Kconfig options:

   • CONFIG_MPSL_CX

   • CONFIG_MPSL_CX_1WIRE

Custom coexistence implementations

To add a custom coexistence implementation, complete following steps:

1. Determine the hardware interface of your PTA. If your PTA uses an interface different from the ones already provided by the nRF Connect SDK, you need to provide a devicetree binding file. See nrf/dts/bindings/radio_coex/generic-radio-coex-three-wire.yaml file for an example.

2. Extend the Kconfig choice CONFIG_MPSL_CX_CHOICE with a Kconfig option allowing to select the new coex implementation.

3. Write the implementation for your PTA. See the nrf/subsys/mpsl/cx/3wire/mpsl_cx_3wire.c file for an example. Add the C source file(s) with the implementation, which must contain the following parts:

   • The implementation of the functions required by the interface structure mpsl_cx_interface_t. Refer to MPSL CX API for details.

   • The initialization code initializing the required hardware resources, based on devicetree information.

   • A call to the function mpsl_cx_interface_set() during the system initialization.

4. Add the necessary CMakeLists.txt entries to get your code compiled when the new Kconfig choice option you added is selected.