MAVLink: raise the serial transmit buffer size to 256 bytes

the 128 byte serial transmit buffer was causing significant problems
with queueing of mavlink messages. With 256 bytes we can fit a lot
more messages out in each pass of the code, which makes telemetry more
efficient

As we discussed on the dev call, we now have enough free ram for this
to be worthwhile

ArduCopter/system.pde

@@ -76,25 +76,12 @@ static void init_ardupilot()
 	// Console serial port
 	//
 	// The console port buffers are defined to be sufficiently large to support
-	// the console's use as a logging device, optionally as the GPS port when
-	// GPS_PROTOCOL_IMU is selected, and as the telemetry port.
-	//
-	// XXX This could be optimised to reduce the buffer sizes in the cases
-	// where they are not otherwise required.
-	//
-	Serial.begin(SERIAL0_BAUD, 128, 128);
+    // the MAVLink protocol efficiently
+    //
+	Serial.begin(SERIAL0_BAUD, 128, 256);
 
 	// GPS serial port.
 	//
-	// Not used if the IMU/X-Plane GPS is in use.
-	//
-	// XXX currently the EM406 (SiRF receiver) is nominally configured
-	// at 57600, however it's not been supported to date.  We should
-	// probably standardise on 38400.
-	//
-	// XXX the 128 byte receive buffer may be too small for NMEA, depending
-	// on the message set configured.
-	//
 	#if GPS_PROTOCOL != GPS_PROTOCOL_IMU
 	Serial1.begin(38400, 128, 16);
 	#endif
@@ -169,11 +156,11 @@ static void init_ardupilot()
     if (!usb_connected) {
         // we are not connected via USB, re-init UART0 with right
         // baud rate
-        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 128);
+        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD));
     }
 #else
     // we have a 2nd serial port for telemetry
-    Serial3.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 128);
+    Serial3.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 256);
 	gcs3.init(&Serial3);
 #endif
 
@@ -620,9 +607,9 @@ static void check_usb_mux(void)
     // the user has switched to/from the telemetry port
     usb_connected = usb_check;
     if (usb_connected) {
-        Serial.begin(SERIAL0_BAUD, 128, 128);
+        Serial.begin(SERIAL0_BAUD);
     } else {
-        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 128);
+        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD));
     }
 }
 #endif

ArduPlane/system.pde

@@ -79,23 +79,12 @@ static void init_ardupilot()
 	// Console serial port
 	//
 	// The console port buffers are defined to be sufficiently large to support
-	// the console's use as a logging device, optionally as the GPS port when
-	// GPS_PROTOCOL_IMU is selected, and as the telemetry port.
+	// the MAVLink protocol efficiently
 	//
-	// XXX This could be optimised to reduce the buffer sizes in the cases
-	// where they are not otherwise required.
-	//
-	Serial.begin(SERIAL0_BAUD, 128, 128);
+	Serial.begin(SERIAL0_BAUD, 128, 256);
 
 	// GPS serial port.
 	//
-	// XXX currently the EM406 (SiRF receiver) is nominally configured
-	// at 57600, however it's not been supported to date.  We should
-	// probably standardise on 38400.
-	//
-	// XXX the 128 byte receive buffer may be too small for NMEA, depending
-	// on the message set configured.
-	//
     // standard gps running
     Serial1.begin(38400, 128, 16);
 
@@ -145,11 +134,11 @@ static void init_ardupilot()
     if (!usb_connected) {
         // we are not connected via USB, re-init UART0 with right
         // baud rate
-        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 128);
+        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD));
     }
 #else
     // we have a 2nd serial port for telemetry
-    Serial3.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 128);
+    Serial3.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 256);
 	gcs3.init(&Serial3);
 #endif
 
@@ -556,9 +545,9 @@ static void check_usb_mux(void)
     // the user has switched to/from the telemetry port
     usb_connected = usb_check;
     if (usb_connected) {
-        Serial.begin(SERIAL0_BAUD, 128, 128);
+        Serial.begin(SERIAL0_BAUD);
     } else {
-        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, 128);
+        Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD));
     }
 }
 #endif