Balena Docker container for using the Pimoroni Enviro+ board

The Enviro+ is a lovely little integrated sensor board for the Raspberry Pi series of boards.

The Pimoroni Getting Started guide is here

Setup

My container should have all needed dependencies and the various examples

You will need to slightly reconfigure your RPi if you are using the particulate sensor as the serial console gets in the way.

If using Balena as your embedded Docker platform you can do something like this

#First disable read-only rootfs:
mount -o remount,rw /

# Then mask the serial getty service:
systemctl mask serial-getty@serial0.service

reboot

You also need a couple of device settings for the I2C and I2S bus

• DT parameters needs to be "i2c_arm=on","spi=on","audio=on","i2s=on"
• DT overlays needs to be pi3-miniuart-bt

For more details on this see the Pimoroni Enviro+ repo

Add USB gadget support

First you must have the "dwc2" overlay setup as above.

Then open a terminal to the host OS and:

mount -o remount,rw /

echo "g_ether" > /etc/modules-load.d/g_ether.conf

mount -o remount,ro /

reboot

This will load the ethernet gadget on boot. You can test this by connecting to a host system and on Linux you should see a new USB ethernet device

Setup Problems downloading container update [Solved]

On the Pi Zero it can take a while to extract container images, particularly if they are quite large.

What can then happen is that a Balena watchdog can then timeout and restart the download, so you end up downloading over and over (quite frustrating!)

See the conversation here where I investigated this.

To resolve you need to edit the timeout on the watchdog and to do this you need to open a terminal in the Host OS, then:

# First disable read-only rootfs:
mount -o remount,rw /

# Edit the service
vi /etc/systemd/system/balena-engine.service

# Change Watchdog Sec in that file to increase it...
WatchdogSec=3600

# Remount ro
mount -o remount,ro /

reboot

Kernel Module Versioning

Also there is an I2S audio driver which is built specifically against the underlying Linux kernel

Check the BelenaOS version of your installation and change this line in Dockerfile.template

ENV VERSION '2.54.2+rev1.prod'

This is built and included for this BalenaOS in the sensors image. To load in use

insmod rpi0-i2s-audio.ko

To check use

arecord -l

You should see an audio device like this

root@539cd3741a89:/usr/src/app# arecord -l
**** List of CAPTURE Hardware Devices ****
card 1: sndrpi0simpleca [snd_rpi0_simple_card], device 0: simple-card_codec_link snd-soc-dummy-dai-0 [simple-card_codec_link snd-soc-dummy-dai-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Environment Variables

There's a sensors container that runs up. This starts autorun.sh which checks for an AUTORUN environment variable. If this isn't present it loops over a sleep function which allows you to debug. Otherwise the container would exit. With this set it runs a runmqtt.sh script which currently runs the default Pimoroni mqtt-all.py script with parameters on the command-line

Environment Variable	Description
AUTORUN	If present we start the main task, otherwise sleep
MQTT_BROKER	MQTT broker host to which to publish data
MQTT_PORT	MQTT broker port
MQTT_TOPIC	MQTT topic we publish to