Garage

This repo contains a kernel driver which allows you to use your RPi as a radio transmitter. It is heavily influenced by RpiTx userspace app, but only supports CW (on/off) modulation.

I built it for the only purpose: to open my garage door using my smart phone. I've got an Apache server running on my RPi with a single page and a cgi-bin script similar to this. This server is only visible within my Wifi network, so Wifi password is effectively used to restricts access to this resource.

Hardware

Connect a piece of wire to GPIO18 pin. Ideally ~2m long, but ~20cm works as well. This is your antenna.

Building

Instructions may vary depending on your RPi version.

Install cross compile toolchain

e.g gcc-linaro-arm-linux-gnueabihf-raspbian-x64

Firmware revision

root@pi:~# zcat /usr/share/doc/raspberrypi-bootloader/changelog.Debian.gz | grep 'firmware as of' | head -1 | sed 's/.*firmware as of //'
2a329e0c7d8ea19c085bac5633aa4fccee0f21be

This is your firmware revision.

Kernel sources

Use your firmware revision to the kernel sources revision:

$ curl https://raw.githubusercontent.com/raspberrypi/firmware/2a329e0c7d8ea19c085bac5633aa4fccee0f21be/extra/git_hash
bc1669c846b629cface0aaa367afb2b9c6226faf

Checkout this revision from https://github.com/raspberrypi/linux.git

.config

root@pi:~# modprobe configs
root@pi:~# gunzip < /proc/config.gz > .config

Download this .config to your buildbox and put it in the root of your kernel source.

Symvers

Use the firmware revision to get the symvers. In the root of kernel source tree run:

curl https://raw.githubusercontent.com/raspberrypi/firmware/2a329e0c7d8ea19c085bac5633aa4fccee0f21be/extra/Module7.symvers > Module.symvers

Set up your shell environment

It's useful to have a script like this.

export PATH=$PATH:~/tmp/rpi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/
export CROSS_COMPILE=arm-linux-gnueabihf-
export ARCH=arm
export KSRC=~/tmp/rpi/linux

You will need to source it each time you want to rebuild the module.

Preparing to build modules

$ make modules_prepare

Building this module

Given you've set up your environment variables like in the steps above, checkout this repo and run

make

Running

Upload built garage-door.ko to RPi and run:

insmod garage-door.ko

Repo contains a test.sh script which contains an example usage.