From 400b6efef7711b054ea06980bc8cd47257014a20 Mon Sep 17 00:00:00 2001
From: Hermes <piotr@piksar.eu>
Date: Tue, 29 Sep 2026 15:23:37 +0200
Subject: [PATCH] feat: gate video and terminal logs on AUX2 state

---
 cmd/groundstation/main.go  | 44 ++++++++++++++++++------------
 cmd/groundstation/video.go | 56 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+), 17 deletions(-)
 create mode 100644 cmd/groundstation/video.go

diff --git a/cmd/groundstation/main.go b/cmd/groundstation/main.go
index 8372767..ceae894 100644
--- a/cmd/groundstation/main.go
+++ b/cmd/groundstation/main.go
@@ -7,7 +7,6 @@ import (
 	"io"
 	"log"
 	"os"
-	"os/exec"
 	"os/signal"
 	"syscall"
 
@@ -18,23 +17,21 @@ import (
 func main() {
 	serialPath := flag.String("serial", "/dev/ttyS0", "GX12 AUX1 UART device")
 	stdin := flag.Bool("stdin", false, "read framed data from standard input")
-	startVideo := flag.Bool("start-video", false, "start fpv-video with Ground Station")
+	videoByAux2 := flag.Bool("video-by-aux2", true, "start fpv-video when AUX2 is above -512")
+	videoCommand := flag.String("video-command", "fpv-video", "video launcher command")
 	flag.Parse()
 
-	if *stdin && *startVideo {
-		log.Fatal("-stdin is intended for protocol tests; omit -start-video")
+	if *stdin {
+		*videoByAux2 = false
 	}
 
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
 
-	if *startVideo {
-		cmd := exec.CommandContext(ctx, "fpv-video")
-		cmd.Stdout, cmd.Stderr = os.Stdout, os.Stderr
-		if err := cmd.Start(); err != nil {
-			log.Fatalf("start fpv-video: %v", err)
-		}
-		defer func() { _ = cmd.Wait() }()
+	var video *videoController
+	if *videoByAux2 {
+		video = newVideoController(*videoCommand)
+		defer func() { _ = video.Stop() }()
 	}
 
 	var input io.Reader = os.Stdin
@@ -49,13 +46,14 @@ func main() {
 		input = port
 	}
 
-	if err := run(ctx, input, os.Stdout); err != nil && err != context.Canceled {
+	if err := run(ctx, input, os.Stdout, video); err != nil && err != context.Canceled {
 		log.Fatal(err)
 	}
 }
 
-func run(ctx context.Context, input io.Reader, output io.Writer) error {
+func run(ctx context.Context, input io.Reader, output io.Writer, video *videoController) error {
 	buf := make([]byte, protocol.RCSize)
+	var previous *protocol.RCFrame
 	for {
 		if err := readRCFrame(ctx, input, buf); err != nil {
 			return err
@@ -65,10 +63,22 @@ func run(ctx context.Context, input io.Reader, output io.Writer) error {
 			log.Printf("discard frame: %v", err)
 			continue
 		}
-		fmt.Fprintf(output, "seq=%d t=%d ch1=%d ch2=%d ch3=%d ch4=%d aux1=%d aux2=%d\n",
-			frame.Sequence, frame.Timestamp,
-			frame.Channels[0], frame.Channels[1], frame.Channels[2], frame.Channels[3],
-			frame.Channels[4], frame.Channels[5])
+		// AUX2 is the dedicated GS video switch: -1024 means management/off,
+		// while its middle position (0) means preflight/WFB/on.
+		if video != nil {
+			if err := video.Set(frame.Channels[5] > -512); err != nil {
+				return err
+			}
+		}
+
+		if previous == nil || previous.Channels != frame.Channels {
+			fmt.Fprintf(output, "seq=%d t=%d ch1=%d ch2=%d ch3=%d ch4=%d aux1=%d aux2=%d\n",
+				frame.Sequence, frame.Timestamp,
+				frame.Channels[0], frame.Channels[1], frame.Channels[2], frame.Channels[3],
+				frame.Channels[4], frame.Channels[5])
+			copy := frame
+			previous = &copy
+		}
 	}
 }
 
diff --git a/cmd/groundstation/video.go b/cmd/groundstation/video.go
new file mode 100644
index 0000000..c6fcc7a
--- /dev/null
+++ b/cmd/groundstation/video.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"sync"
+)
+
+// videoController owns the optional fpv-video launcher. It never touches WFB
+// directly; fpv-video remains the sole owner of the video receiver lifecycle.
+type videoController struct {
+	command string
+	mu      sync.Mutex
+	cmd     *exec.Cmd
+	done    chan error
+}
+
+func newVideoController(command string) *videoController {
+	return &videoController{command: command}
+}
+
+func (v *videoController) Set(active bool) error {
+	v.mu.Lock()
+	defer v.mu.Unlock()
+
+	if active {
+		if v.cmd != nil {
+			return nil
+		}
+		v.cmd = exec.Command(v.command)
+		v.cmd.Stdout, v.cmd.Stderr = os.Stdout, os.Stderr
+		if err := v.cmd.Start(); err != nil {
+			v.cmd = nil
+			return fmt.Errorf("start %s: %w", v.command, err)
+		}
+		v.done = make(chan error, 1)
+		cmd := v.cmd
+		go func() { v.done <- cmd.Wait() }()
+		return nil
+	}
+
+	if v.cmd == nil {
+		return nil
+	}
+	if err := v.cmd.Process.Signal(os.Interrupt); err != nil {
+		return fmt.Errorf("stop %s: %w", v.command, err)
+	}
+	<-v.done
+	v.cmd, v.done = nil, nil
+	return nil
+}
+
+func (v *videoController) Stop() error {
+	return v.Set(false)
+}