Trying to access raspberry GPIO from a docker container.

Simple python script which reads temperature and humidity sensors and send it to a MQTT broker.

• DHT sensor on D4
• build with sudo docker compose build

For the container, challenge are:

• access to the GPIO
• pretend to be a raspberry board

Access to the GPIO

According to this SO answer, Running the container in privileged mode works. I didn't succeed by mapping --device /dev/gpiomem.

Pretend to be a raspberry board

Adafruit_dht lib depends on adafruit_platformdetect lib and RPi.GPIO. These try to determine the board model through config files which are usually present with Raspbian.

It is up to you to find the right infos for your board thanks to lib examples below.

adafruit_platformdetect

Lib example:

from adafruit_platformdetect import Detector
detector = Detector()
print("Chip id: ", detector.chip.id)   # Chip id:  BCM2XXX
print("Board id: ", detector.board.id) # Board id:  RASPBERRY_PI_3A_PLUS

Source code

It tries to read env vars before analyzing config files. So simply add this to the compose file:

    environment:
      - BLINKA_FORCECHIP=BCM2XXX
      - BLINKA_FORCEBOARD=RASPBERRY_PI_3A_PLUS

RPi.GPIO

Lib example:

import RPi.GPIO as GPIO
print(GPIO.RPI_INFO)

Source code

It reads the following config files:

• /proc/device-tree/system/linux,revision
• /proc/cpuinfo

Focus on /proc/cpuinfo only. The lib tries to find a line beginning with Hardware : BCMxxxx. On my raspbian installation, the line doesn't exist. So I copy-paste and edit the file.

cp /proc/cpuinfo proc-cpuinfo  #copy paste
chmod 644 proc-cpuinfo         #change permission for writing
nano proc-cpuinfo              #edit the file and add , for example, `Hardware        : BCM2837`

Then bind the file to the container. So in compose file:

    volumes:
      - ./proc-cpuinfo:/proc/cpuinfo:ro