AP_Mount: set clock on SIYI

this means photos on microSD have correct date

libraries/AP_Mount/AP_Mount_Siyi.cpp

@@ -6,6 +6,7 @@
 #include <GCS_MAVLink/GCS.h>
 #include <GCS_MAVLink/include/mavlink/v2.0/checksum.h>
 #include <AP_SerialManager/AP_SerialManager.h>
+#include <AP_RTC/AP_RTC.h>
 
 extern const AP_HAL::HAL& hal;
 
@@ -68,6 +69,17 @@ void AP_Mount_Siyi::update()
         } else {
             request_configuration();
         }
+
+#if AP_RTC_ENABLED
+        // send UTC time to the camera
+        if (sent_time_count < 5) {
+            uint64_t utc_usec;
+            if (AP::rtc().get_utc_usec(utc_usec) &&
+                send_packet(SiyiCommandId::SET_TIME, (const uint8_t *)&utc_usec, sizeof(utc_usec))) {
+                sent_time_count++;
+            }
+        }
+#endif
     }
 
     // request attitude at regular intervals

libraries/AP_Mount/AP_Mount_Siyi.h

@@ -112,6 +112,7 @@ private:
         SET_CAMERA_IMAGE_TYPE = 0x11,
         READ_RANGEFINDER = 0x15,
         EXTERNAL_ATTITUDE = 0x22,
+        SET_TIME = 0x30,
     };
 
     // Function Feedback Info packet info_type values
@@ -335,6 +336,9 @@ private:
         const char* model_name;
     };
     static const HWInfo hardware_lookup_table[];
+
+    // count of SET_TIME packets, we send 5 times to cope with packet loss
+    uint8_t sent_time_count;
 };
 
 #endif // HAL_MOUNT_SIYISERIAL_ENABLED