CC3D - Use Flex port in I2C mode unless USART3 is used. Add I2C drivers

for compass, baro and display.

Makefile

@@ -381,7 +381,12 @@ CC3D_SRC	 = \
 		   drivers/accgyro_spi_mpu6000.c \
 		   drivers/adc.c \
 		   drivers/adc_stm32f10x.c \
+		   drivers/barometer_bmp085.c \
+		   drivers/barometer_ms5611.c \
 		   drivers/bus_spi.c \
+		   drivers/bus_i2c_stm32f10x.c \
+		   drivers/compass_hmc5883l.c \
+		   drivers/display_ug2864hsweg01.c \
 		   drivers/gpio_stm32f10x.c \
 		   drivers/inverter.c \
 		   drivers/light_led_stm32f10x.c \

docs/Board - CC3D.md

@@ -79,6 +79,22 @@ The SoftSerial port is not available when RX_PARALLEL_PWM is used. The transmiss
 
 To connect the GUI to the flight controller you need additional hardware attached to the USART1 serial port (by default).
 
+# Flex Port
+
+The flex port will be enabled in I2C mode unless USART3 is used.  You can connect external I2C sensors and displays to this port.
+
+You cannot use USART3 and I2C at the same time.
+
+## Flex port pinout
+
+| Pin | Signal             | Notes                   |
+| --- | ------------------ | ----------------------- |
+| 1   | GND                |                         |
+| 2   | VCC unregulated    |                         |
+| 3   | I2C SCL / UART3 TX | 3.3v level              |
+| 4   | I2C SDA / UART3 RX | 3.3v level (5v tolerant |
+
+
 # Flashing
 
 There are two primary ways to get Cleanflight onto a CC3D board.

src/main/main.c

@@ -206,12 +206,15 @@ void init(void)
 #endif
 
 #ifdef USE_I2C
-#ifdef NAZE
+#if defined(NAZE)
     if (hardwareRevision != NAZE32_SP) {
         i2cInit(I2C_DEVICE);
     }
+#elif defined(CC3D)
+    if (!doesConfigurationUsePort(SERIAL_PORT_USART3)) {
+        i2cInit(I2C_DEVICE);
+    }
 #else
-    // Configure the rest of the stuff
     i2cInit(I2C_DEVICE);
 #endif
 #endif

src/main/target/CC3D/target.h

@@ -47,8 +47,18 @@
 
 #define ACC_SPI_MPU6000_ALIGN CW270_DEG
 
+// External I2C BARO
+#define BARO
+#define USE_BARO_MS5611
+#define USE_BARO_BMP085
+
+// External I2C MAG
+#define MAG
+#define USE_MAG_HMC5883
+
 #define INVERTER
 #define BEEPER
+#define DISPLAY
 
 #define USE_USART1
 #define USE_USART3
@@ -69,6 +79,9 @@
 #define USE_SPI_DEVICE_1
 #define USE_SPI_DEVICE_2
 
+#define USE_I2C
+#define I2C_DEVICE (I2CDEV_2) // Flex port - SCL/PB10, SDA/PB11
+
 #define USE_ADC
 
 #define CURRENT_METER_ADC_GPIO      GPIOB