Defensive code for Heltec Display (#1296)

Added to Heltec board display code logic to reduce corruption of messages on the display

Two piece of defensive code were added

- Only display messages to the display when operating on Core 1 ( Default Arduino ESP32 CONFIG_ARDUINO_RUNNING_CORE )

- Only display one character/string at a time

In the event of failure, default to Serial output.

PS SSD1306 driver similar issues

https://github.com/ThingPulse/esp8266-oled-ssd1306/issues/326
https://github.com/ThingPulse/esp8266-oled-ssd1306/issues/352

main/ZboardHeltec.ino

@@ -32,7 +32,8 @@
 #if defined(ZboardHELTEC)
 #  include "ArduinoLog.h"
 #  include "config_HELTEC.h"
-// #  include "heltec.h"
+
+SemaphoreHandle_t semaphoreOLEDOperation;
 
 void logToLCD(bool display) {
   display ? Log.begin(LOG_LEVEL_LCD, &Oled) : Log.begin(LOG_LEVEL, &Serial); // Log on LCD following LOG_LEVEL_LCD
@@ -125,6 +126,10 @@ OledSerial::OledSerial(int x) {
 
 void OledSerial::begin() {
   // Heltec.begin(); // User OMG serial support
+
+  semaphoreOLEDOperation = xSemaphoreCreateBinary();
+  xSemaphoreGive(semaphoreOLEDOperation);
+
   display->init();
   display->flipScreenVertically();
   display->setFont(ArialMT_Plain_10);
@@ -157,18 +162,9 @@ void OledSerial::fillScreen(OLEDDISPLAY_COLOR color) {
   display->fillRect(0, 0, OLED_WIDTH, OLED_HEIGHT);
 }
 
-size_t OledSerial::write(uint8_t c) {
-  display->clear();
-  display->setColor(WHITE);
-  display->setFont(ArialMT_Plain_10);
-
-  display->write((char)c);
-  display->drawLogBuffer(0, 0);
-  display->display();
-  return 1;
-}
-
 size_t OledSerial::write(const uint8_t* buffer, size_t size) {
+  if (xPortGetCoreID() == CONFIG_ARDUINO_RUNNING_CORE) {
+    if (xSemaphoreTake(semaphoreOLEDOperation, pdMS_TO_TICKS(30000)) == pdTRUE) {
       display->clear();
       display->setColor(WHITE);
       display->setFont(ArialMT_Plain_10);
@@ -178,8 +174,13 @@ size_t OledSerial::write(const uint8_t* buffer, size_t size) {
       }
       display->drawLogBuffer(0, 0);
       display->display();
+      xSemaphoreGive(semaphoreOLEDOperation);
       return size;
     }
+  }
+  // Default to Serial output if the display is not available
+  return Serial.write(buffer, size);
+}
 
 /*
 Display OpenMQTTGateway logo - borrowed from ZboardM5.ino and tweaked for ssd1306 display ( removed color and tweaked size/location )

main/config_HELTEC.h

@@ -87,7 +87,12 @@ public:
 
   void fillScreen(OLEDDISPLAY_COLOR); // fillScreen display and set color
 
-  size_t write(uint8_t);
+  // This is a bit of lazy programmer simplifacation for the semapore and core detecting code.  Not sure if it is truly space efficient.
+
+  inline size_t write(uint8_t x) {
+    return write(&x, 1);
+  }
+
   size_t write(const uint8_t* buffer, size_t size);
   inline size_t write(const char* buffer, size_t size) {
     return write((uint8_t*)buffer, size);