feat: simple sensor panels with file-based data source (#7)

* add simulation mode for easier development

* improved sensor file watcher, poc cpu & mem usage

Trigger file read by rename event

* feat: system information sensor tool

Gather various sensor values with the sysinfo crate:
https://github.com/GuillaumeGomez/sysinfo
Values can be written to a sensor source file with the `--out` cmd line
option for the `asterctl` tool.

* ci: build sysinfo tool and include in build artifact

* feat: support integerDigits, decimalDigits sensor value format options

* docs: update documentation

Closes #6

linux/scripts/cpu_usage.sh

@@ -0,0 +1,73 @@
+#!/bin/bash
+# Simple proof-of-concept Linux shell script to periodically write the CPU usage into a sensor text file.
+#
+# A single sensor `cpu_percent` is written to the sensor file containing the overall cpu usage in percent.
+# CPU usage is calculated every second.
+#
+# CPU usage logic from:
+# https://stackoverflow.com/questions/9229333/how-to-get-overall-cpu-usage-e-g-57-on-linux
+#
+set -e
+set -o pipefail
+
+REFRESH=1
+TEMP_DIR="${TMPDIR:-/tmp}"
+TMP_SENSOR_FILE="${TEMP_DIR}/cpu.txt.tmp"
+SENSOR_FILE="${TEMP_DIR}/sensors/cpu.txt"
+
+#=============================================================
+
+usage() {
+  cat << EOF
+Simple PoC script to periodically write the CPU usage into a sensor text file.
+
+Usage:
+$0 [-r REFRESH] [-s SENSOR_FILE] [-t TEMP_DIR]
+
+  -r REFRESH     refresh in seconds.  Default: $REFRESH
+  -s SENSOR_FILE output sensor file.  Default: $SENSOR_FILE
+  -t TEMP_DIR    temporary directory. Default: $TEMP_DIR
+
+EOF
+  exit 1
+}
+
+#=============================================================
+
+#------------------------------------------------------------------------------
+# Start of script
+#------------------------------------------------------------------------------
+# check command line arguments
+while getopts "r:s:t:h" opt; do
+  case ${opt} in
+    "r")
+      REFRESH="$OPTARG"
+      ;;
+    "s")
+      SENSOR_FILE="$OPTARG"
+      ;;
+    "t")
+      TMP_SENSOR_FILE="$OPTARG/cpu.txt.tmp"
+      ;;
+    h )
+        usage
+        ;;
+    : )
+        echo "Option: -$OPTARG requires an argument" 1>&2
+        usage
+        ;;
+   \? )
+        echo "Invalid option: -$OPTARG" 1>&2
+        usage
+        ;;
+  esac
+done
+
+mkdir -p "$(dirname "$SENSOR_FILE")"
+
+while :
+do
+  USAGE=$({ head -n1 /proc/stat;sleep "$REFRESH";head -n1 /proc/stat; } | awk '/^cpu /{u=$2-u;s=$4-s;i=$5-i;w=$6-w}END{print "cpu_percent:"int(0.5+100*(u+s+w)/(u+s+i+w))}')
+  echo "$USAGE" > "$TMP_SENSOR_FILE"
+  mv "$TMP_SENSOR_FILE" "$SENSOR_FILE"
+done

linux/scripts/mem_usage.sh

@@ -0,0 +1,84 @@
+#!/bin/bash
+# Simple proof-of-concept Linux shell script to periodically write the memory usage into a sensor text file.
+#
+# The following sensor values are written to the sensor file.
+# - memory_total in bytes
+# - memory_free in bytes
+# - memory_available in bytes
+# - memory_usage in percent
+#
+# Memory usage is calculated every five seconds.
+
+set -e
+set -o pipefail
+
+REFRESH=5
+TEMP_DIR="${TMPDIR:-/tmp}"
+TMP_SENSOR_FILE="${TEMP_DIR}/mem.txt.tmp"
+SENSOR_FILE="${TEMP_DIR}/sensors/mem.txt"
+
+#=============================================================
+
+usage() {
+  cat << EOF
+Simple PoC script to periodically write the memory usage into a sensor text file.
+
+Usage:
+$0 [-r REFRESH] [-s SENSOR_FILE] [-t TEMP_DIR]
+
+  -r REFRESH     refresh in seconds.  Default: $REFRESH
+  -s SENSOR_FILE output sensor file.  Default: $SENSOR_FILE
+  -t TEMP_DIR    temporary directory. Default: $TEMP_DIR
+
+EOF
+  exit 1
+}
+
+#=============================================================
+
+#------------------------------------------------------------------------------
+# Start of script
+#------------------------------------------------------------------------------
+# check command line arguments
+while getopts "r:s:t:h" opt; do
+  case ${opt} in
+    "r")
+      REFRESH="$OPTARG"
+      ;;
+    "s")
+      SENSOR_FILE="$OPTARG"
+      ;;
+    "t")
+      TMP_SENSOR_FILE="$OPTARG/mem.txt.tmp"
+      ;;
+    h )
+        usage
+        ;;
+    : )
+        echo "Option: -$OPTARG requires an argument" 1>&2
+        usage
+        ;;
+   \? )
+        echo "Invalid option: -$OPTARG" 1>&2
+        usage
+        ;;
+  esac
+done
+
+mkdir -p "$(dirname "$SENSOR_FILE")"
+
+while :
+do
+  MEM_TOTAL=$(grep MemTotal /proc/meminfo | awk '{print $2}')
+  MEM_FREE=$(grep MemFree /proc/meminfo | awk '{print $2}')
+  MEM_AVAILABLE=$(grep MemAvailable /proc/meminfo | awk '{print $2}')
+
+  printf "memory_total:%d\nmemory_free:%d\nmemory_available:%d\nmemory_usage:%d\n" \
+    "$MEM_TOTAL" \
+    "$MEM_FREE" \
+    "$MEM_AVAILABLE" \
+    $(((MEM_TOTAL - MEM_AVAILABLE) * 100 / MEM_TOTAL)) > "$TMP_SENSOR_FILE"
+  mv "$TMP_SENSOR_FILE" "$SENSOR_FILE"
+
+  sleep "$REFRESH"
+done