openlabs blog

It turns out that Linux's 802.15.4 implementation is just about ready to facilitate promiscuous packet sniffing natively. With minimal patching, we can now use a Raspberry Pi and 802.15.4 radio to sniff raw 802.15.4 packets using Wireshark or tcpdump or whatever.

Here I'll demonstrate the method I've come to prefer: Sniffing packets on the RPi with tcpdump and sending them over wifi using netcat to Wireshark running on another (less graphically laggy) computer.

Here I document a case of compiling on Lubuntu 14.04 and flashing with lpc21isp through the openOBC's micro-USB port. This is what I'd recommend as probably the most supported setup.

The same steps can work on a variety of systems, but I'm doing this with a fresh install of Lubuntu 14.04 in Virtualbox. A normal install will have just about everything we need out of the box, but we'll probably have to install an arm-none-eabi toolchain and lpc21isp, and we may have to install git.

Yeah, I finally got around to installing an oil pressure sensor in my E36 and trying it out with my openOBC. It was one of those really bizarre experiences where everything just worked without a fight.

The pressure sensor I used is a VDO 360-007. It's an 80 psi sensor with M12x1.5 threads and a warning light output at 8.5 psi. It fit perfectly in place of the factory pressure switch I replaced with it and the gauge output on it connects to the analog.in1 or in2 pins of the openOBC board, which are both set up by default to work with grounded resistive sensors like this.

6LoWPAN support in the Linux kernel is sufficiently new right now that you can't just use any old kernel version - you have to ensure you're using a new enough kernel if you want to do anything useful. This presents a problem since the custom kernel normally used on the Raspberry Pi is forked from an older version of the kernel. Fortunately however, support for the RPi in the vanilla kernel has reached the point where we can now run a vanilla Linux kernel on the RPi rather than the custom RPi kernel.

Actually, even the mainline kernel does not currently have sufficiently complete 6LoWPAN and 802.15.4 code to interoperate well with other platforms like Contiki OS. Our task therefore is to get the net-next kernel running on an RPi.

The net-next kernel is a branch maintained by David Miller which holds a variety of network-related changesets as they make their way into the mainline branch. As far as I know, net-next is where all 6LoWPAN and 802.15.4 Linux development is taking place and is the preferred kernel branch to work from right now if you're using either.

Previously, development had been occurring on David Miller's net-next branch. Alexander Aring now maintains linux-wpan and linux-wpan-next branches based on bluetooth and bluetooth-next, as well as a fork of the userspace tools here. Fortunately this change between branches does not seem to have caused any problems with running on the RPi.

Substituting a vanilla Linux kernel for the forked RPi Linux kernel is simple enough, but there are some noteworthy obstacles. First is that booting a vanilla kernel will require us to use U-Boot *, which the RPi does not use by default. Second is that RPi support in the vanilla kernel is not 100% done yet. The complete list of omissions is unknown to me, but I believe HDMI is the main thing that's missing. Fortunately for us though, everything that we need to turn the RPi into a 6LoWPAN border router is working.

Aside from that, this won't be too different from compiling a kernel in any other case.