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--- doc:appunti:hardware:raspberrypi_thermostat [2022/01/12 15:21] – [Installing on Raspberry Pi OS 2021-10-30 Bullseye] niccolo
+++ doc:appunti:hardware:raspberrypi_thermostat [2022/01/12 17:11] (current) – [Installing the old Adafruit LCD library] niccolo
@@ Line 659: / Line 659: @@
 ==== Installing the new Adafruit LCD library ====
+**WARNING**: Do not use this library on the old Raspberry Pi model B, it is too CPU intensive! Use the old one.
 **WARNING**: The new library is more CPU intensive than the old one. I opened an **[[https://github.com/adafruit/Adafruit_CircuitPython_PCD8544/issues/16|issue on GitHub]]**. So I decided to give-up with the new library and use the old one (see below for installation tips). Here you can see a CPU utilization graph, the first half is using the old library, the second half is using the new one:
@@ Line 708: / Line 710: @@
 ==== Installing the old Adafruit LCD library ====
-As reported above, the new **Adafruit CircuitPython PCD8544** library is more CPU intensive than the old discontinued one **[[https://github.com/adafruit/Adafruit_Nokia_LCD|Adafruit Nokia LCD]]**. Fortunately enough, the old library does run with Python 3, and I was able to use it on my old Raspberry Pi model B over the operating system derived from Debian 11 Bullseye. So the average CPU usage is **lower than 10%**, instead than **above 30%**!
+As reported above, the old and discontinued library **[[https://github.com/adafruit/Adafruit_Nokia_LCD|Adafruit Nokia LCD]]** is less CPU intensive than the new **Adafruit CircuitPython PCD8544**. Fortunately enough, the old library does run with Python 3, and I was able to use it on my old Raspberry Pi model B over the operating system derived from Debian 11 Bullseye. So the average CPU usage is **lower than 10%**, instead than **above 30%**!
+The library is not available from the **[[https://pypi.org/|PyPI]]** repository, so it must be downloaded from the GitHub repository. The library depends upon **Adafruit_GPIO**, which in turn requires **Adafruit_PureIO** and **spidev**. The two Adafruit libraries are available from PyPI, for **spidev** we installed the Debian packaged version.
+<code>
+apt install python3-spidev
+mkdir -p /usr/local/download/Adafruit-GPIO
+cd /usr/local/download/Adafruit-GPIO
+pip3 download Adafruit-GPIO
+pip3 install Adafruit_PureIO-1.1.9-py3-none-any.whl
+pip3 install Adafruit_GPIO-1.0.3-py3-none-any.whl
+</code>
+We download the library from its **GitHub repository** and install it using **pip3**:
+<code>
+cd /usr/local/download
+git clone https://github.com/adafruit/Adafruit_Nokia_LCD.git
+cd Adafruit_Nokia_LCD/
+pip3 install .
+</code>
+The dependencies tree is the following:
+  * Adafruit_Nokia_LCD
+    * Adafruit_GPIO
+      * Adafruit_PureIO
+      * spidev
-FIXME Describe the installation.
 ==== Installing the Telegram Bot Python library ====
@@ Line 735: / Line 763: @@
 pip3 install telepot-12.7-py3-none-any.whl
 </code>
+==== Starting the protherm service at bootstrap ====
+Raspberry Pi OS based on **Debian 11 Bullseye** uses **systemd** to start services on bootstrap. The **protherm** service requires the **/dev/spidev0.0** device to be available on start, otherwise it starts with the LCD disabled. Unfortunately the timing at which the kernel enables the device cannot be predicted, so we have to take some precautions to let systemd wait for the spidev device before starting protherm.
+First of all we create an //udev// rule; the rule will force //systemd// to create a "systemd device" when the kernel device becomes available. The rule is created into a file named **/etc/udev/rules.d/protherm-spidev.rules**:
+<file>
+# Inform systemd when the kernel device /dev/spidev0.0 becomes available.
+# Systemd will create a systemd device named "dev-spidev0.0.device", which
+# can be used to trigger the start of a service.
+ACTION=="add", SUBSYSTEM=="spidev", KERNEL=="spidev0.0", TAG+="systemd"
+</file>
+We use three keywords that must matched (because of the **%%==%%** sign) during an udev event. If the event is of type device **add**, the device belongs to the **spidev** subsystem and the kernel device name is **spidev0.0**, //udev// adds the string **systemd** to the **TAG** key associated to the device itself.
+Systemd includes the **systemd-udevd.service** which will notice every device tagged witht the string **systemd** and dynamically creates a **device unit**. In this case the unit will be called **dev-spidev0.0.device**. You can ask systemd to list all the existing device units (because of the **%%--all%%** option, also the short name is listed):
+<code>
+systemctl list-units --all --type=device
+...
+  dev-spidev0.0.device   loaded active   plugged /dev/spidev0.0
+...
+</code>
+If the systemd device does not exist, it probably means that the udev rule did not worked as expected. Thanks to this systemd device unit, we can write a protherm systemd unit that will start the service only after the device is instantiated by the kernel. The systemd unit will be **/etc/systemd/system/protherm.service**:
+<file>
+[Unit]
+Description=Programmable Thermostat Service
+After=syslog.target
+# Wait for spidev0.0 systemd device to be available.
+After=dev-spidev0.0.device
+Requires=dev-spidev0.0.device
+[Service]
+Type=simple
+WorkingDirectory=/tmp/
+ExecStart=/usr/local/sbin/protherm -f
+[Install]
+WantedBy=multi-user.target
+</file>
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