ANT_SEL pin of nRF21540 using nRF Connect SDK

[Samuele Forconi]

Hi,

we have a Gateway board that uses the nRF52832 with the nRF21540.

The firmware running on the nRF52832 is a slightly modified version of the HCI UART sample found in the nRF Connect SDK.

We have created the new board files (dts etc.) for porting the HCI UART firmware on our board and everything is working correctly (the firmware compiles correctly and the HCI UART is working and I am able to see advertising packets coming when I start a scan procedure).

Our hardware has 2 antennas, connected to the nRF21540, 1 internal antenna and 1 external antenna (with uFL connector).

I would like to build 1 firmware that use the internal antenna and 1 firmware that use the external antenna (for 2 different products that shares the same board).

The DTS file for the board that I have created is the following:

/dts-v1/;
#include <nordic/nrf52832_qfaa.dtsi>
#include "tinygateway_flex-pinctrl.dtsi"

/ {
	model = "Custom Board auto generated by nRF Connect for VS Code";
	compatible = "BlueUp,tinygateway-flex";
	
	chosen {
		zephyr,console = &uart0;
		zephyr,shell-uart = &uart0;
		zephyr,uart-mcumgr = &uart0;
		zephyr,bt-mon-uart = &uart0;
		zephyr,bt-c2h-uart = &uart0;
		zephyr,sram = &sram0;
		zephyr,flash = &flash0;
		zephyr,code-partition = &slot0_partition;
	};
	
	leds {
		compatible = "gpio-leds";

		led0: led_0 {
			gpios = <&gpio0 20 GPIO_ACTIVE_LOW>;
			label = "Blue LED 0";
		};
	};
	
	nrf_radio_fem: nrf21540_fem {
		compatible = "nordic,nrf21540-fem";
		tx-en-gpios = <&gpio0 28 GPIO_ACTIVE_HIGH>;
		rx-en-gpios = <&gpio0 30 GPIO_ACTIVE_HIGH>;
		pdn-gpios = <&gpio0 16 GPIO_ACTIVE_HIGH>;
		ant-sel-gpios = <&gpio0 29 GPIO_ACTIVE_HIGH>;
		mode-gpios = <&gpio0 27 GPIO_ACTIVE_HIGH>;
		spi-if = <&nrf_radio_fem_spi>;
		supply-voltage-mv = <3000>;
	};
	
	/* These aliases are provided for compatibility with samples */
	aliases {
		led0 = &led0;
	};
};

&reg {
	regulator-initial-mode = <NRF5X_REG_MODE_DCDC>;
};

&adc {
	status = "okay";
};

&uicr {
	gpio-as-nreset;
};

&gpiote {
	status = "okay";
};

&gpio0 {
	status = "okay";
};

&uart0 {
	compatible = "nordic,nrf-uarte";
	status = "okay";
	current-speed = <115200>;
	pinctrl-0 = <&uart0_default>;
	pinctrl-1 = <&uart0_sleep>;
	pinctrl-names = "default", "sleep";
};

fem_spi: &spi0 {
	status = "okay";
	cs-gpios = <&gpio0 12 GPIO_ACTIVE_LOW>;
	pinctrl-0 = <&spi0_default>;
	pinctrl-1 = <&spi0_sleep>;
	pinctrl-names = "default", "sleep";

	nrf_radio_fem_spi: nrf21540_fem_spi@0 {
		compatible = "nordic,nrf21540-fem-spi";
		status = "okay";
		reg = <0>;
		spi-max-frequency = <8000000>;
	};
};

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

&flash0 {
	partitions {
		compatible = "fixed-partitions";
		#address-cells = <1>;
		#size-cells = <1>;

		boot_partition: partition@0 {
			label = "mcuboot";
			reg = <0x00000000 DT_SIZE_K(48)>;
		};

		slot0_partition: partition@c000 {
			label = "image-0";
			reg = <0x0000c000 DT_SIZE_K(220)>;
		};

		slot1_partition: partition@43000 {
			label = "image-1";
			reg = <0x00043000 DT_SIZE_K(220)>;
		};

		storage_partition: partition@7a000 {
			label = "storage";
			reg = <0x0007a000 DT_SIZE_K(24)>;
		};
	};
};

In the Kconfig files I did not see any reference to the antenna selection, so my question is: how should I select the antenna to use for the nRF21540?

Thanks for the support.

BR,

Samuele.

[Kazi Afroza Sultana]

Hello Samuele,

There is no kconfig options for antenna selection on nRF21540. Antenna selection is hardware controlled done through the ANT_SEL pin of the FEM which already you have done in the device tree.

There is one API https://docs.nordicsemi.com/bundle/nrf-apis-latest/page/group_fem_al_gade636165bd57936884a26ade1885f856.html you can use to select antenna from software by using this fem_antenna_select().

API defines the following enumeration

enum fem_antenna {
    FEM_ANTENNA_1,
    FEM_ANTENNA_2
};

and the function looks like

int fem_antenna_select(enum fem_antenna ant);

Can call this function like this

#include <include/fem_al/fem_al.h>

void select_ant1(void)
{
    fem_antenna_select(FEM_ANTENNA_1);  // to Use ANT1
}

void select_ant2(void)
{
    fem_antenna_select(FEM_ANTENNA_2);  // to Use ANT2
}

Thanks.

BR
Kazi

[Samuele Forconi]

Hi Kazi,

thanks for your hint.

Before your suggestion I managed to compile 2 firmwares each with different antenna selection by toggling the ACTIVE_LOW / ACTIVE_HIGH pin on the board DTS file (not the very best way, but it worked...).

Thanks for pointing me to that fem API, I will try to use it.

BR

Samuele.