A kernel module that powers the CC2520 802.15.4 radio in Linux.

The general idea is to create a character driver that exposes 802.15.4 frames to the end user, allowing them to test and layer different networking stacks from user-land onto the CC2520 radio. We're specifically targeting running the IPv6 TinyOS networking stack on a Raspberry Pi.

To compile you'll need an ARM cross compiler and the source tree of a compiled ARM kernel. Update the Makefile to point to your kernel source, and run the following command:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-

Please note that we're cross-compiling from an x86 machine.

Currently this process requires compiling against the 3.6 version of the Linux kernel from the Raspberry Pi's GitHub.

Start by creating a folder to group all of the code needed to compile this kernel module.

mkdir rpi
cd rpi

Now get the source. You'll need to get the Raspberry Pi 3.6 kernel source and this repository.

git clone git://github.com/raspberrypi/linux.git
git clone git://github.com/ab500/linux-cc2520-driver.git

Now you need to patch two files in the linux tree. The first changes a small part of the device configuration to let the SPI driver know where it can find DMA-accessible memory. The second updates the spi driver to msperl's version and changes the spi driver to deassert the chip-select line. Not keeping the SPI_CS_TA flag active will have the SPI driver toggle the CS pin between transmissions. The CC2520 radio requires a SPI toggle to terminate command sequences that don't have a predetermined length.

cd linux
git apply ../linux-cc2520-driver/patches/bcm2708.patch
git apply ../linux-cc2520-driver/patches/spi-bcm2708.patch

Finally you're ready to compile the kernel for the Pi. First make sure you have the right build environment. You'll need an ARM GCC cross-compiler installed (arm-linux-gnueabi-gcc).

Follow the instructions on the Raspberry Pi main site under the section "Perform the compilation". You do not need to transfer all of the modules or anything, but you do have to build them.

http://elinux.org/RPi_Kernel_Compilation#Perform_the_compilation

To compile this module update the Makefile with the path of the RPi linux source. Then:

cd ~\rpi\linux-cc2520-driver
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-

To install you will want to start with an RPi already running Raspbian. Make sure you are using version 2013-02-09-wheezy-raspbian or later.

You need to copy the recompiled kernel, the SPI kernel module, and the CC2520 kernel module to the RPi.

cd ~/rpi
scp linux/arch/arm/boot/Image <RPI>:/boot/kernel.img
scp linux/drivers/spi/spi-bcm2708.ko <RPI>:/lib/modules/3.6.11+/kernel/drivers/spi/
scp linux-cc2520-driver/cc2520.ko <RPI>:/lib/modules/3.6.11+/kernel/drivers/misc/

Now that we've gotten the kernel installed we need to enable automatic loading of the SPI driver at boot. Edit /etc/modprobe.d/raspi-blacklist.conf and comment out the line that blacklists the SPI driver from boot. It should look like this when you're done:

# blacklist spi and i2c by default (many users don't need them)
#blacklist spi-bcm2708
blacklist i2c-bcm2708

Now enable the cc2520 driver at boot. Edit /etc/modules to look like:

# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
# Parameters can be specified after the module name.

snd-bcm2835
cc2520

Lastly, force the system to find the new cc2520.ko driver:

sudo depmod -a

Now that everything is setup you can run the driver and test that it works.

To do this I use SFTP.

sftp pi@your-pi-hostname

sftp> put tests/read.c
sftp> put tests/write.c

gcc write.c -o write
gcc read.c -o read

First check the kern.log file for the debug output above. Also make sure your raspberry pi hasn't frozen and paniced. You're doing pretty good.

Next you'll need another 802.15.4 mote. I've been using Epic-based devices. Use the SimpleSackTest app in the shed and install it on a mote. It simply sends an 802.15.4 packet with an incrementing counter in it, requesting an ACK, and will ACK any packets sent to it. On a standard mote the LEDs are setup to indicate the following:

• Blue - Toggles every time a packet is properly acknowledged by the radio.
• Green - Toggles every time a packet is sent by the mote.
• Red - Toggles every time the mote successfully receives a packet.

When the RPi radio is off only the green light will blink. Running the write and read apps on the RPi will cause all the lights to blink.

The output will look something like this:

read.c

Receiving a test message...
result 14
read  0x0D 0x61 0x88 0xD4 0x22 0x00 0x01 0x00 0x01 0x00 0x76 0xD5 0x13 0xEB
Receiving a test message...
result 14
read  0x0D 0x61 0x88 0xD5 0x22 0x00 0x01 0x00 0x01 0x00 0x76 0xD6 0x13 0xEB
Receiving a test message...
result 14
read  0x0D 0x61 0x88 0xD6 0x22 0x00 0x01 0x00 0x01 0x00 0x76 0xD7 0x13 0xEB
Receiving a test message...
result 14
read  0x0D 0x61 0x88 0xD7 0x22 0x00 0x01 0x00 0x01 0x00 0x76 0xD8 0x13 0xEA

write.c

Sending a test message...
result 12
Sending a test message...
result 12
Sending a test message...
result 12
Sending a test message...
result 12
Sending a test message...
result 12
Sending a test message...
result 12

The driver is starting to shape up to be feature-complete. Looking for obscure timing bugs at the moment, but we support LPL, CSMA/CA, unique filtering, and Soft-ACK features. It's basically a fully-featured radio implementing something that's really close to the default TinyOS radio stack.

It runs more-or-less a generic, standard MAC layer. Nothing fancy.