Add i2c clock

roles/i2c-clock/files/etc/modules-load.d/rtc-ds1307.conf

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+rtc-ds1307

roles/i2c-clock/files/etc/systemd/system/rtc-i2c.service

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+[Unit]
+ConditionCapability=CAP_SYS_TIME
+ConditionVirtualization=!container
+DefaultDependencies=no
+Wants=dev-rtc_i2c.device
+After=dev-rtc_i2c.device
+Before=systemd-timesyncd.service ntpd.service chrony.service
+
+[Service]
+Type=oneshot
+CapabilityBoundingSet=CAP_SYS_TIME
+PrivateTmp=yes
+ProtectSystem=full
+ProtectHome=yes
+DeviceAllow=/dev/rtc_i2c rw
+DevicePolicy=closed
+ExecStart=/usr/bin/echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device && /sbin/hwclock --s
+
+[Install]
+WantedBy=time-sync.target

roles/i2c-clock/files/etc/udev/rules.d/55-rtc-i2c.rules

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+#/lib/udev/rules.d/50-udev-default.rules:SUBSYSTEM=="rtc", ATTR{hctosys}=="1", SYMLINK+="rtc"
+#/lib/udev/rules.d/50-udev-default.rules:SUBSYSTEM=="rtc", KERNEL=="rtc0", SYMLINK+="rtc", OPTIONS+="link_priority=-100"
+
+# I2C RTC, when added and not the source of the sys clock (kernel), is used ;
+# separate name to ensure rtc-i2c.service will not be run on anything else
+ACTION=="add", SUBSYSTEMS=="i2c", SUBSYSTEM=="rtc", KERNEL=="rtc0", ATTR{hctosys}=="0", SYMLINK+="rtc_i2c", TAG+="systemd"

roles/i2c-clock/tasks/install.yml

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+---
+- become: yes
+  block:
+    - name: install i2c-tools
+      become: yes
+      apt:
+        update_cache: yes
+        pkg:
+          - i2c-tools
+
+    - name: enable automatic module load
+      copy:
+        src: etc/modules-load.d/rtc-ds1307.conf
+        dest: /etc/modules-load.d/rtc-ds1307.conf
+
+    - name: add systemd service
+      copy:
+        src: etc/systemd/system/rtc-i2c.service
+        dest: /etc/systemd/system/rtc-i2c.service
+
+    - name: enable systemd service
+      systemd:
+        name: rtc-i2c.service
+        enabled: yes
+        state: started

roles/i2c-clock/tasks/main.yml

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+---
+- import_tasks: install.yml
+
+- import_tasks: set-time.yml
+
+- import_tasks: remove-fake-clock.yml

roles/i2c-clock/tasks/remove-fake-clock.yml

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+---
+- name: uninstall fakehw
+  become: yes
+  apt:
+    update_cache: yes
+    state: absent
+    pkg:
+      - fake-hwclock

roles/i2c-clock/tasks/set-time.yml

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+---
+- become: yes
+  block:
+    - name: load hwclock
+      shell:
+        cmd: |
+          modprobe rtc-ds1307
+          echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device
+    - name: update time
+      shell:
+        cmd: |
+          hwclock -w
+    - name: read time
+      shell:
+        cmd: |
+          hwclock -r