feat: Suspend/Resume Support via Systemd

docs/index.md

@@ -17,6 +17,8 @@ This tool is a daemon process that can be used to sync the two keyboard halves f
 
 You may want to setup this tool to run at startup. Depending on your distribution `systemd` is a likely solution. See <https://github.com/arjun024/systemd-example-startup> for an example. If you installed via the AUR package this is setup automatically.
 
+_NOTE:_ libusb does NOT raise a `HOTPLUG_EVENT_DEVICE_LEFT` event on suspend (at least on Linux). This means the sync script doesn't know the keyboard handles are invalid upon resuming. Two address this two `systemd` scripts can be used. See the `systemd/` directory in the repo. The AUR package takes this approach.
+
 ### Run
 
     $ dumang-sync

systemd/dumang-sync-python.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=DuMang DK6 Layer Sync (Python Invoke)
+
+[Service]
+Type=Simple
+ExecStart=dumang-sync
+
+[Install]
+WantedBy=multi-user.target

systemd/dumang-sync.service

@@ -1,9 +1,16 @@
 [Unit]
 Description=DuMang DK6 Layer Sync
+# NOTE: Two systemd services are required since on suspend, libusb does NOT raise a HOTPLUG_EVENT_DEVICE_LEFT
+# event. This means the sync script doesn't know the keyboard handles are invalid upon resuming.
+# TODO: Is this expected behavior on part of libusb or a bug?
+Before=sleep.target
+StopWhenUnneeded=yes
 
 [Service]
-Type=Simple
-ExecStart=dumang-sync
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=-/bin/systemctl stop dumang-sync-python.service
+ExecStop=-/bin/systemctl start dumang-sync-python.service
 
 [Install]
-WantedBy=multi-user.target
+WantedBy=sleep.target