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--- doc:appunti:hardware:raspberrypi_thermostat [2022/01/12 16:13] – [Starting the protherm service at bootstrap] 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 743: / Line 771: @@
 <file>
-# Create a systemd device "dev-spidev0.0.device" to trigger the start of the service.
+# Inform systemd when the kernel device /dev/spidev0.0 becomes available.
-SUBSYSTEM=="spidev", KERNEL=="spidev0.0", TAG+="systemd"
+# 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 two keywords that must be matched (because of the **%%==%%** sign) during a device event: if the event is triggered by 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.
+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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