The driver provides a character device and a few sysfs attributes, allowing for simple wireless communication with another Raspberry Pi or perhaps an Arduino with the same nRF905 chip.

/dev/nrf905

Allowed operations are write and read. The file can be opened for both read and write operations (r+ mode, see man 3 fopen for further details).

Read and write operations only work with 32 bytes at a time (the size of the buffer on the nRF905 chip). If a different size is used, EMSGSIZE is returned.

/sys/bus/spi/devices/spi0.0/frequency

The frequency (in kHz) that the transceiver is tuned to. Allowed ranges are [422400, 473600) and [844800, 947200), with rounding to 100kHz in the former and 200kHz in the latter case. The lower bound is included in both cases, the upper is excluded. Both HFREQ_PLL and CH_NO are set based on the frequency written to this sysfs attribute.

/sys/bus/spi/devices/spi0.0/pa_pwr

Output power. Allowed values are from 0 to 3 (both inclusive).

• 0: -10dBm
• 1: -2dBm
• 2: +6dBm
• 3: +10dBm

/sys/bus/spi/devices/spi0.0/rx_address

The address used when receiving. At the moment, the driver supports only 4-byte addresses.

/sys/bus/spi/devices/spi0.0/tx_address

The address used when transmitting. At the moment, the driver supports only 4-byte addresses.

This needs to be done only once per boot.

sudo sh -c "echo -n ABCD > /sys/bus/spi/devices/spi0.0/rx_address"
sudo sh -c "echo -n ABCD > /sys/bus/spi/devices/spi0.0/tx_address"
sudo sh -c "echo -n 868000 > /sys/bus/spi/devices/spi0.0/frequency"
sudo sh -c "echo -n 3 > /sys/bus/spi/devices/spi0.0/pa_pwr"

sudo dd if=/dev/nrf905 bs=32 count=1 2>/dev/null | hexdump -Cv

sudo dd if=/dev/urandom bs=32 count=1 of=/dev/nrf905

For normal usage, you should change the permissions (see man 1 chmod), but that is out of the scope of this document.

At the moment of writing, the current version is 2016-11-25 and the lite edition has been used while writing this document.

See https://www.raspberrypi.org/documentation/installation/installing-images/README.md for instructions on how to make a bootable SD card.

sudo apt-get update
sudo apt-get dist-upgrade

sudo apt-get install linux-image-4.4.0-1-rpi2 linux-image-rpi2-rpfv linux-headers-rpi2-rpfv

Note: Use rpi instead of rpi2 if you have the original Raspberry Pi.

Edit /boot/config.txt and add the following lines

# use the rpfv kernel
kernel=vmlinuz-4.4.0-1-rpi2
initrd=initrd.img-4.4.0-1-rpi2 followkernel

Note: Use rpi instead of rpi2 if you have the original Raspberry Pi.

sudo reboot

uname -r

If everything is correct, the output should be

4.4.0-1-rpi2

git clone https://github.com/ICBTech/nRF905.git

make
make dtb

sudo make modules_install
sudo make dtb_install
sudo depmod -a

sudo modprobe nrf905

dmesg | grep nrf905

If everything is correct, the output should be

[   79.829085] nrf905_init

The timestamp would, of course, be different.

Edit /boot/config.txt and add the following lines

# load our custom overlay
dtoverlay=nrf905

In that same file, also uncomment the line to enable spi

# enable spidev
dtparam=spi=on

sudo reboot

sudo modprobe nrf905

dmesg | grep nrf905

If everything is correct, the output should be

[   25.095296] nrf905_init
[   25.096562] nrf905 spi0.0: nrf905_probe
[   25.096615] nrf905 spi0.0: gpio_pwr_up: 17
[   25.096627] nrf905 spi0.0: gpio_trx_ce: 27
[   25.096638] nrf905 spi0.0: gpio_tx_en: 22
[   25.096649] nrf905 spi0.0: gpio_dr: 18

The timestamps would, of course, be different. Compared to the previous run of the same command, the output now also contains lines where the driver is probed (bound to the spi address defined in the dts file).

Edit /etc/modules and add the following line

nrf905