From e81214a22f53caa5112a8a68e78ea954ac98f0eb Mon Sep 17 00:00:00 2001
From: Julian Oes <julian@oes.ch>
Date: Wed, 4 Nov 2020 11:08:30 +0100
Subject: [PATCH] mavlink: avoid double trigger using sequence

By adding the sequence number we can avoid double triggering due to
command retransmissions. This is according to the mavlink spec for
MAV_CMD_IMAGE_START_CAPTURE.
---
 src/modules/mavlink/streams/CAMERA_TRIGGER.hpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/modules/mavlink/streams/CAMERA_TRIGGER.hpp b/src/modules/mavlink/streams/CAMERA_TRIGGER.hpp
index 127904e9aa..295ea92dc4 100644
--- a/src/modules/mavlink/streams/CAMERA_TRIGGER.hpp
+++ b/src/modules/mavlink/streams/CAMERA_TRIGGER.hpp
@@ -70,6 +70,7 @@ private:
 		0,	//target_sys_id
 		MAV_COMP_ID_CAMERA // active_comp_id
 	};
+	int _sequence {1};
 
 	bool send() override
 	{
@@ -90,7 +91,7 @@ private:
 				vcmd.param1 = 0.0f; // all cameras
 				vcmd.param2 = 0.0f; // duration 0 because only taking one picture
 				vcmd.param3 = 1.0f; // only take one
-				vcmd.param4 = NAN;
+				vcmd.param4 = (float)_sequence++;
 				vcmd.param5 = (double)NAN;
 				vcmd.param6 = (double)NAN;
 				vcmd.param7 = NAN;