Check system uptime before SDR startup delay.

Throw a system error in developer mode if the uptime is greater than
120s and `sdrWatcher()` is restarted (usually a systemd restart).

main/sdr.go

@@ -10,6 +10,7 @@
 package main
 
 import (
+	"fmt"
 	"log"
 	"os/exec"
 	"regexp"
@@ -17,6 +18,7 @@ import (
 	"strings"
 	"sync"
 	"sync/atomic"
+	"syscall"
 	"time"
 
 	"../godump978"
@@ -471,7 +473,21 @@ func sdrWatcher() {
 	prevUATEnabled := false
 	prevESEnabled := false
 
-	time.Sleep(90 * time.Second)
+	// Get the system (RPi) uptime.
+	info := syscall.Sysinfo_t{}
+	err := syscall.Sysinfo(&info)
+	if err == nil {
+		// Got system uptime. Delay if and only if the system uptime is less than 120 seconds. This should be plenty of time
+		//  for the RPi to come up and start Stratux. Keeps the delay from happening if the daemon is auto-restarted from systemd.
+		if info.Uptime < 120 {
+			time.Sleep(90 * time.Second)
+		} else if globalSettings.DeveloperMode {
+			// Throw a "critical error" if developer mode is enabled. Alerts the developer that the daemon was restarted (possibly)
+			//  unexpectedly.
+			daemonRestartedErr := fmt.Errorf("System uptime %d seconds. Daemon restarted.\n")
+			addSystemError(daemonRestartedErr)
+		}
+	}
 
 	for {
 		time.Sleep(1 * time.Second)