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dts: bindings: improve nordic,nrf21540-fem docs

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The way the nRF21540 device is configured makes sense once you
understand it, but it's quite unusual: a single peripheral is
configured with two separate devicetree nodes linked by a phandle.

Since this risks entering "exploding head" territory for beginners, it
deserves a thorough example. Add one to the binding's description.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
This commit is contained in:
Martí Bolívar 2021-11-05 13:32:07 -07:00 committed by Carles Cufí
parent 9bbaccc8ed
commit a930bebb42
1 changed files with 53 additions and 2 deletions
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55
dts/bindings/net/wireless/nordic,nrf21540-fem.yaml
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@ -1,9 +1,60 @@
# Copyright (c) 2020 Nordic Semiconductor ASA
# Copyright (c) 2020, 2021 Nordic Semiconductor ASA
# SPDX-License-Identifier: Apache-2.0
description: |
This is a representation of the nRF21540 Radio Front-End module
This is a representation of the nRF21540 Radio Front-End module.
See the "nordic,nrf21540-fem-spi" binding to configure the SPI
interface. The SPI interface should be configured as a child node
of the SPI bus you have connected to the FEM. Then you "connect"
the FEM and SPI configurations using the spi-if property.
Here is an example nRF21540 configuration with a SPI interface
selected, using the SPIM0 peripheral found on several nRF5 SoCs:
&spi0 {
compatible = "nordic,nrf-spim";
status = "okay";
cs-gpios = <&gpio1 3 GPIO_ACTIVE_LOW>;
/* ... MISO/MOSI/SCK pin configuration goes here ... */
my_spi_if: nrf21540-spi@0 {
compatible = "nordic,nrf21540-fem-spi";
reg = <0>;
spi-max-frequency = <8000000>;
};
};
nrf_radio_fem: nrf21540 {
compatible = "nordic,nrf21540-fem";
tx-en-gpios = <&gpio0 2 GPIO_ACTIVE_HIGH>;
rx-en-gpios = <&gpio0 5 GPIO_ACTIVE_HIGH>;
spi-if = <&my_spi_if>;
pdn-gpios = <...>;
ant-sel-gpios = <...>;
mode-gpios = <...>;
/* ... other nRF21540 properties go here ... */
};
In the above example, the nRF21540 is configured for use with:
- TX_EN on P0.2 (from 'tx-en-gpios')
- RX_EN on P0.5 (from 'rx-en-gpios')
- SPI communication via SPIM0 (the bus, or parent node, of
the 'my_spi_if' node
- CSN on P1.3 (from index 0 in the bus node's 'cs-gpios' property)
You must perform any additional required SPI pin configuration
(nRF21540 MISO, MOSI, and SCK pins) within the SPI bus node
('spi0' in the above example). See your SPI node's binding for
details on these pin mux properties. You can use any SPI node
available in your SoC's devicetree.
Configure any other nRF21540 pins as needed using 'pdn-gpios',
'ant-sel-gpios', and 'mode-gpios' properties. If unsure about the
format, use 'tx-en-gpios' as an example.
compatible: "nordic,nrf21540-fem"
include: base.yaml