DISPLAY - Allow FC to boot normally if OLED display is not connected at

boot.  FC can detect when the display is unplugged and recovers after
display I2C timeouts.

src/main/drivers/display_ug2864hsweg01.c

@@ -169,14 +169,15 @@ static const uint8_t const multiWiiFont[][5] = { // Refer to "Times New Roman" F
         };
 
 #define OLED_address   0x3C     // OLED at address 0x3C in 7bit
-void i2c_OLED_send_cmd(uint8_t command)
+
+static bool i2c_OLED_send_cmd(uint8_t command)
 {
-    i2cWrite(OLED_address, 0x80, command);
+    return i2cWrite(OLED_address, 0x80, command);
 }
 
-static void i2c_OLED_send_byte(uint8_t val)
+static bool i2c_OLED_send_byte(uint8_t val)
 {
-    i2cWrite(OLED_address, 0x40, val);
+    return i2cWrite(OLED_address, 0x40, val);
 }
 
 void i2c_OLED_clear_display(void)
@@ -247,9 +248,14 @@ void i2c_OLED_send_string(const char *string)
 * according to http://www.adafruit.com/datasheets/UG-2864HSWEG01.pdf Chapter 4.4 Page 15
 */
 #if 1
-void ug2864hsweg01InitI2C(void)
+bool ug2864hsweg01InitI2C(void)
 {
-    i2c_OLED_send_cmd(0xAE); // Set display OFF
+
+    // Set display OFF
+    if (!i2c_OLED_send_cmd(0xAE)) {
+        return false;
+    }
+
     i2c_OLED_send_cmd(0xD4); // Set Display Clock Divide Ratio / OSC Frequency
     i2c_OLED_send_cmd(0x80); // Display Clock Divide Ratio / OSC Frequency
     i2c_OLED_send_cmd(0xA8); // Set Multiplex Ratio
@@ -272,7 +278,10 @@ void ug2864hsweg01InitI2C(void)
     i2c_OLED_send_cmd(0xA4); // Set all pixels OFF
     i2c_OLED_send_cmd(0xA6); // Set display not inverted
     i2c_OLED_send_cmd(0xAF); // Set display On
+
     i2c_OLED_clear_display();
+
+    return true;
 }
 #else
 void ug2864hsweg01InitI2C(void)

src/main/drivers/display_ug2864hsweg01.h

@@ -34,7 +34,7 @@
 #define VERTICAL_BARGRAPH_ZERO_CHARACTER (128 + 32)
 #define VERTICAL_BARGRAPH_CHARACTER_COUNT 7
 
-void ug2864hsweg01InitI2C(void);
+bool ug2864hsweg01InitI2C(void);
 
 void i2c_OLED_set_xy(uint8_t col, uint8_t row);
 void i2c_OLED_set_line(uint8_t row);

src/main/io/display.c

@@ -73,6 +73,7 @@ controlRateConfig_t *getControlRateConfig(uint8_t profileIndex);
 #define PAGE_CYCLE_FREQUENCY (MILLISECONDS_IN_A_SECOND * 5)
 
 static uint32_t nextDisplayUpdateAt = 0;
+static bool displayPresent = false;
 
 static rxConfig_t *rxConfig;
 
@@ -136,7 +137,7 @@ typedef struct pageState_s {
 static pageState_t pageState;
 
 void resetDisplay(void) {
-    ug2864hsweg01InitI2C();
+    displayPresent = ug2864hsweg01InitI2C();
 }
 
 void LCDprint(uint8_t i) {
@@ -211,11 +212,6 @@ void showTitle()
 
 void handlePageChange(void)
 {
-    // Some OLED displays do not respond on the first initialisation so refresh the display
-    // when the page changes in the hopes the hardware responds.  This also allows the
-    // user to power off/on the display or connect it while powered.
-    resetDisplay();
-
     i2c_OLED_clear_display_quick();
     showTitle();
 }
@@ -533,9 +529,22 @@ void updateDisplay(void)
     }
 
     if (pageState.pageChanging) {
-        handlePageChange();
         pageState.pageFlags &= ~PAGE_STATE_FLAG_FORCE_PAGE_CHANGE;
         pageState.nextPageAt = now + PAGE_CYCLE_FREQUENCY;
+
+        // Some OLED displays do not respond on the first initialisation so refresh the display
+        // when the page changes in the hopes the hardware responds.  This also allows the
+        // user to power off/on the display or connect it while powered.
+        resetDisplay();
+
+        if (!displayPresent) {
+            return;
+        }
+        handlePageChange();
+    }
+
+    if (!displayPresent) {
+        return;
     }
 
     switch(pageState.pageId) {