DHT11 for CHIP

This repo contains the collated and modified source code for one stop dht11 support for C.H.I.P:

• dht11 kernel module modified to set 24 MHz PIO Interrupt Clock Select automatically.
• Device tree overlay autoload systemd oneshot service.
• Device tree overlays for 2 sensors. One connected to PWM0 (dht11@1) and the other to AP-EINT3 (dht11@0).
• Test script probe-dht11 in /usr/bin

Installing

Check the deb packages under Releases for the easiest install process.

dpkg -i dht11-chip-1.0-1.deb
systemctl enable autoload-dtbo
systemctl start autoload-dtbo

Corresponding iio device should now be available. Once the DHT11 has been connected the connection can be tested by running the provided test script.

> probe-dth11
[2017-08-18T20:44:01+0300 - dht11@0]: T=24.0C RH=34.0%
[2017-08-18T20:44:03+0300 - dht11@0]: T=24.0C RH=34.0%
[2017-08-18T20:44:05+0300 - dht11@0]: T=24.0C RH=34.0%

Only AP-EINT3 is initially configured with device tree overlays. Move *.dtbo files from /opt/autoload-dtbo/disabled /opt/autoload-dtbo/enabled or vice versa to change this configuration. Other device tree overlays can also be loaded using the same service.

Included works

This repo collates files from multiple sources. However, all of the collated code happens to be licensed under GPLv2+.

Building

Tools & dependencies

The kernel

CHIP-linux kernel of the 4.4.13-ntc-mlc branch is needed for building components. Grab the tip of debian/4.4.13-ntc-mlc branch as a shallow copy and prepare it for modules. Note the LOCALVERSION parameter that is required to later build compatible kernel modules.

git clone --single-branch --branch debian/4.4.13-ntc-mlc --depth 1 https://github.com/NextThingCo/CHIP-linux.git
cd CHIP-linux
make LOCALVERSION= modules_prepare

Device tree compiler

Debian ships dtc 1.4.0 for the next decade or so. Get and compile 1.4.4 from dgibson's repo. Alternative solution would be to grab the sources from Linux git repo, but Mr. Gibson seems to be a maintainer for dtc making the difference neglible.

apt-get install bison flex
git clone --single-branch --branch v1.4.4 --depth 1 https://github.com/dgibson/dtc.git
cd dtc
make NO_PYTHON=1
cp dtc /usr/local/bin/

make install did not seem to work as intended for v1.4.4 tag. However, you can always fall back to the good old cp.

Building

Build the kernel module and dts files by running make. The build script expects to find CHIP-linux at path ~/CHIP-linux. If this is not the case you'll have to use env parameters to guide make.

make ChipLinux=[path to CHIP-linux]

Install/uninstall local build

Provided Makefiles should make installing and uninstalling as simple as running make install and make uninstall.

Packaging

Everything is packaged into a deb package by running make all package. The will be placed in package-workdir/dht11-chip-[version]-[pkg revision].deb. The resulting package does not comply with any sensible packaging guidelines. However, it works quite well to deliver the required files to a CHIP.