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Buildroot External structure for DigitalRoosterGui

Buildroot external for creating a root file system running DigitalRoosterGui as digital alarm clock.

This repository is part of a larger project. For more information head to

Supported hardware

For detailed information on the hardware check out This software includes configurations for Raspberry Pi Zero W and Banana Pi M2 Zero. The Raspberry Pi port works great while Banana Pi is still under development. We have to figure out the performance issues i.e. why it takes ages for the display to update after a touch event. I don't consider this port production ready yet.

The device tree and kernel drivers include support for following hardware:

  • Adafruit PiTFT2.8" capacitive touch

  • The DigitalRooster-MK3B extension board which is compatible both Raspberry Pi and Banana Pi M2 Zero.

    • Three Channel audio using a 3W MAX98357A I2S driver. Since this IC is a Class-D amp I equipped the channels with passive LC filter to improve audio quality. The left/right channels have a cut-off frequency of around 20kHz while the mid channel filter is a 16kHz low-pass

    • a hardware shutdown line for the audio codecs so 'off' is really 'off' and there is no popping noise when changing tracks

    • A BQ32000 Real Time Clock chip with trickle-charge circuit that charges a 200mF SuperCap. Although the software synchronizes time using NTP I wanted a Real Time Clock in case the network is down. Also having a the correct time during boot makes logging a lot more insightful and avoids TLS error for certificates that are not yet valid on Jan 1st of 1970...

    • A TLC59208F PWM LED driver for backlight control and a possible RGBA light to wake up with a sunrise simulation. The PWM pins on both Raspberry Pi and BananaPi are scarce an used for other functions, e.g. I2S. Software PWM is not really a nice option so I was willing to spend some 2.5$ for a nice I2C chip that integrates nicely with the Linux LED driver framework

    • Integrated circuitry for the Grayhill rotary encoder 61C11-01-08-02 that requires voltage dividers and a debounce for the push button

    • The possiblity to connect an external I2C device. I have a APDS9660 gesture and light sensor in mind for dynamic back-light control or gesture snooze.

Alternatively you can use the Adafruit Speaker Bonnet with MAX98357 I2S amp to get sound. It works with Raspberry Pi (but not BananaPi) and unfortunately does not have a hardware shutdown pin.

DigitalRooster on hardware DigitalRooster Mk3b extension board


Copyright 2018 by Thomas Ruschival

Licensed under the GNU PUBLIC LICENSE Version 2. The license terms can be found in the file LICENSE

Build Pre-requisites

  • buildroot installation git clone git://


mkdir <build_tree>
make BR2_EXTERNAL=<local_clone_of_this_repo> -C<buildroot_installation_dir> \
     O=<build_tree> XXX_defconfig
cd <build_tree>
make menuconfig (optional)

Tip: in the build tree create a file where you can set individual buildroot variables for your system like for instance the root password. See buildroot manual Following example uses ccache, overrides the hostname, root password and the source location for DigitalRoosterGui.



Target build configurations

Currently the following configurations (XXX_defconfig) for exist:

  • rpi0w_defconfig DigitalRooster on a Raspberry Pi Zero W (currently running at my bedside)

  • bananapi_m2_zero_defconfig DigitalRooster on a BananaPi M2 Zero ( in development )

Environment variables

Some properties that are very specific to your home such as wifi is configured through environment variables.

Wifi Network configuration

boards/common/ has a hook to configure wifi network passwords.

Set the environment variable LOCAL_WIFI_NET_CFG to a file path containing your wifi network configuration. The content of this file will be added to /etc/wpa_supplicant.conf of your target file system.

SSH public key file

boards/common/ has a hook to a public key to /root/.ssh/authorized_keys.

Set your environment variable LOCAL_SSH_PUBKEY to the public key file of the identity you want to use for ssh authentication.

Signed SWUpdate images (optional)

SWUpdate installed with rpi0w_defconfig is configured to verify image signatures. Once compiled with signed image verification this feature is no longer optional. This means if you want to use sw-update images to update your DigitalRooster you have to create signed images.

To do this you need a public certificate that is installed on DigitalRooster and will be used by sw-update to verify your image. You will also need a private key to sign your image.

These to files are passed to the build by two environment variables:

  • The variable SWU_IMAGE_CERT_PATH contains the path of the public certificate that will be installed in /etc/ssl/certs/sw-update-cert.pem used for validating signatures at runtime.
  • The environment variable SWU_IMAGE_SIG_KEY_PATH contains the path to a path of the private RSA key matching the public cert used for signing in the .swu file.

To create the key and the ceritficate follow the documentation of Update images from verified source

Example for the whole build process

For the anxious and impatient among you here is a copy-and-paste runthrough. The only thing I can't give you is the SSID and passphrase of your wifi...

  1. Create a wpa_supplicant.conf fragment for the wifi-key and SSID
mkdir digitalrooster
cd digitalrooster
export TOPDIR=$(pwd)

cat > $TOPDIR/my_wifi_conf << EOF
  1. Checkout the repositories
git clone git://
git clone
  1. Create image signing keys and certificate (optional)
# Create a unencrypted key (not recommended)
openssl genrsa -out $TOPDIR/swupdate-key.pem
export SWU_IMAGE_SIG_KEY_PAT=$TOPDIR/swupdate-key.pem
# Create the certificate for this key
openssl rsa -in swupdate-key.pem -out $TOPDIR/swupdate-pub-cert.pem -outform PEM -pubout
export SWU_IMAGE_CERT_PATH=$TOPDIR/swupdate-pub-cert.pem
  1. Configure and build
mkdir build-rpi0w
cd build-rpi0w
make BR2_EXTERNAL=$TOPDIR/buildroot_digitalrooster -C$TOPDIR/buildroot \
     O=$(pwd) rpi0w_defconfig

# this takes some time......
# copy image to sdcard
dd if=./images/sdcard.img of=/dev/sde bs=512