Make yield() overridable (espressif#2991)

Author: dok-net

cores/esp32/HardwareSerial.h

@@ -97,10 +97,12 @@ class HardwareSerial: public Stream
     uart_t* _uart;
 };
 
+extern void serialEventRun(void) __attribute__((weak));
+
 #if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SERIAL)
 extern HardwareSerial Serial;
 extern HardwareSerial Serial1;
 extern HardwareSerial Serial2;
 #endif
 
-#endif
+#endif // HardwareSerial_h

cores/esp32/esp32-hal-misc.c

@@ -44,11 +44,13 @@ float temperatureRead()
     return (temprature_sens_read() - 32) / 1.8;
 }
 
-void yield()
+void __yield()
 {
     vPortYield();
 }
 
+void yield() __attribute__ ((weak, alias("__yield")));
+
 #if CONFIG_AUTOSTART_ARDUINO
 
 extern TaskHandle_t loopTaskHandle;

cores/esp32/main.cpp

@@ -17,6 +17,7 @@ void loopTask(void *pvParameters)
             esp_task_wdt_reset();
         }
         loop();
+        if (serialEventRun) serialEventRun();
     }
 }