AP_OSD: Fixed UART thread ownership for the MSP DisplayPort OSD Backend

libraries/AP_OSD/AP_OSD.cpp

@@ -320,6 +320,9 @@ void AP_OSD::init()
 #if OSD_ENABLED
 void AP_OSD::osd_thread()
 {
+    // initialize thread specific code once
+    backend->osd_thread_run_once();
+
     while (true) {
         hal.scheduler->delay(100);
         update_osd();

libraries/AP_OSD/AP_OSD_Backend.h

@@ -56,6 +56,9 @@ public:
     // copy the backend specific symbol set to the OSD lookup table
     virtual void init_symbol_set(uint8_t *symbols, const uint8_t size);
 
+    // called by the OSD thread once
+    virtual void osd_thread_run_once() { return; }
+
     AP_OSD * get_osd()
     {
         return &_osd;

libraries/AP_OSD/AP_OSD_MSP_DisplayPort.cpp

@@ -50,6 +50,14 @@ bool AP_OSD_MSP_DisplayPort::init(void)
     return true;
 }
 
+// called by the OSD thread once
+void AP_OSD_MSP_DisplayPort::osd_thread_run_once()
+{
+    if (_displayport != nullptr) {
+        _displayport->init_uart();
+    }
+}
+
 void AP_OSD_MSP_DisplayPort::clear(void)
 {
     // clear remote MSP screen

libraries/AP_OSD/AP_OSD_MSP_DisplayPort.h

@@ -24,6 +24,10 @@ public:
     // copy the backend specific symbol set to the OSD lookup table
     void init_symbol_set(uint8_t *lookup_table, const uint8_t size) override;
 
+    // called by the OSD thread once
+    // used to initialize the uart in the correct thread
+    void osd_thread_run_once() override;
+
 
 protected:
     uint8_t format_string_for_osd(char* dst, uint8_t size, bool decimal_packed, const char *fmt, va_list ap) override;