AP_GPS: Use GPS_COM_PORT param in GSOF driver

* Instead of hard coding to COM2, allow users to set it
* The enum is confusing, so this needs a wiki entry
* Use the same port in requestBAUD
* If the user configures an invalid param, send an error
* Add values for the GSOF COM ports
* Fix bug in RS232 being port 3 instead of port 0
* Use set_default for the typical user value when the GSOF driver is run

Signed-off-by: Ryan Friedman <ryanfriedman5410+github@gmail.com>

libraries/AP_GPS/AP_GPS.cpp

@@ -356,17 +356,18 @@ const AP_Param::GroupInfo AP_GPS::var_info[] = {
 #if AP_GPS_SBF_ENABLED
     // @Param: _COM_PORT
     // @DisplayName: GPS physical COM port
-    // @Description: The physical COM port on the connected device, currently only applies to SBF GPS
+    // @Description: The physical COM port on the connected device, currently only applies to SBF and GSOF GPS
     // @Range: 0 10
     // @Increment: 1
     // @User: Advanced
+    // @Values: 0:COM1(RS232) on GSOF, 1:COM2(TTL) on GSOF
     // @RebootRequired: True
     AP_GROUPINFO("_COM_PORT", 23, AP_GPS, _com_port[0], HAL_GPS_COM_PORT_DEFAULT),
 
 #if GPS_MAX_RECEIVERS > 1
     // @Param: _COM_PORT2
     // @DisplayName: GPS physical COM port
-    // @Description: The physical COM port on the connected device, currently only applies to SBF GPS
+    // @Description: The physical COM port on the connected device, currently only applies to SBF and GSOF GPS
     // @Range: 0 10
     // @Increment: 1
     // @User: Advanced

libraries/AP_GPS/AP_GPS_GSOF.cpp

@@ -29,6 +29,7 @@
 #include "AP_GPS_GSOF.h"
 #include <AP_Logger/AP_Logger.h>
 #include <AP_HAL/utility/sparse-endian.h>
+#include <GCS_MAVLink/GCS.h>
 
 #if AP_GPS_GSOF_ENABLED
 
@@ -57,10 +58,15 @@ AP_GPS_GSOF::AP_GPS_GSOF(AP_GPS &_gps, AP_GPS::GPS_State &_state,
     
     msg.state = Msg_Parser::State::STARTTX;
 
-    // baud request for port 0
-    requestBaud(0);
-    // baud request for port 3
-    requestBaud(3);
+    constexpr uint8_t default_com_port = static_cast<uint8_t>(HW_Port::COM2);
+    gps._com_port[state.instance].set_default(default_com_port);
+    const auto com_port = gps._com_port[state.instance].get();
+    if (!validate_com_port(com_port)) {
+        // The user parameter for COM port is not a valid GSOF port
+        GCS_SEND_TEXT(MAV_SEVERITY_ERROR, "GSOF instance %d has invalid COM port setting of %d", state.instance, com_port);
+        return;
+    }
+    requestBaud(static_cast<HW_Port>(com_port));
 
     const uint32_t now = AP_HAL::millis();
     gsofmsg_time = now + 110;
@@ -74,8 +80,13 @@ AP_GPS_GSOF::read(void)
     const uint32_t now = AP_HAL::millis();
 
     if (gsofmsgreq_index < (sizeof(gsofmsgreq))) {
+        const auto com_port = gps._com_port[state.instance].get();
+        if (!validate_com_port(com_port)) {
+            // The user parameter for COM port is not a valid GSOF port
+            return false;
+        }
         if (now > gsofmsg_time) {
-            requestGSOF(gsofmsgreq[gsofmsgreq_index], HW_Port::COM2, Output_Rate::FREQ_10_HZ);
+            requestGSOF(gsofmsgreq[gsofmsgreq_index], static_cast<HW_Port>(com_port), Output_Rate::FREQ_10_HZ);
             gsofmsg_time = now + 110;
             gsofmsgreq_index++;
         }
@@ -150,11 +161,11 @@ AP_GPS_GSOF::parse(const uint8_t temp)
 }
 
 void
-AP_GPS_GSOF::requestBaud(const uint8_t portindex)
+AP_GPS_GSOF::requestBaud(const HW_Port portindex)
 {
     uint8_t buffer[19] = {0x02,0x00,0x64,0x0d,0x00,0x00,0x00, // application file record
                           0x03, 0x00, 0x01, 0x00, // file control information block
-                          0x02, 0x04, portindex, 0x07, 0x00,0x00, // serial port baud format
+                          0x02, 0x04, static_cast<uint8_t>(portindex), 0x07, 0x00,0x00, // serial port baud format
                           0x00,0x03
                          }; // checksum
 
@@ -347,4 +358,16 @@ AP_GPS_GSOF::process_message(void)
 
     return false;
 }
+
+bool
+AP_GPS_GSOF::validate_com_port(const uint8_t com_port) const {
+    switch(com_port) {
+        case static_cast<uint8_t>(HW_Port::COM1):
+        case static_cast<uint8_t>(HW_Port::COM2):
+            return true;
+        default:
+            return false;
+    }
+}
+
 #endif

libraries/AP_GPS/AP_GPS_GSOF.h

@@ -44,7 +44,7 @@ private:
     // Ethernet, USB, etc are not supported by the GPS driver at this time so they are omitted.
     // These values are not documented in the API.
     enum class HW_Port {
-        COM1 = 3, // RS232 serial
+        COM1 = 0, // RS232 serial
         COM2 = 1, // TTL serial
     };
 
@@ -58,12 +58,13 @@ private:
 
     bool parse(const uint8_t temp) WARN_IF_UNUSED;
     bool process_message() WARN_IF_UNUSED;
-    void requestBaud(const uint8_t portindex);
 
-    // Send a request to the GPS to enable a message type on the port at the specified rate.
+    // Send a request to the GPS to set the baud rate on the specified port.
     // Note - these request functions currently ignore the ACK from the device.
     // If the device is already sending serial traffic, there is no mechanism to prevent conflict.
     // According to the manufacturer, the best approach is to switch to ethernet.
+    void requestBaud(const HW_Port portIndex);
+    // Send a request to the GPS to enable a message type on the port at the specified rate.
     void requestGSOF(const uint8_t messageType, const HW_Port portIndex, const Output_Rate rateHz);
 
     double SwapDouble(const uint8_t* src, const uint32_t pos) const WARN_IF_UNUSED;
@@ -72,6 +73,7 @@ private:
     uint16_t SwapUint16(const uint8_t* src, const uint32_t pos) const WARN_IF_UNUSED;
 
     bool validate_baud(const uint8_t baud) const WARN_IF_UNUSED;
+    bool validate_com_port(const uint8_t com_port) const WARN_IF_UNUSED;
 
     struct Msg_Parser
     {