allow to set pin to OUTPUT_OPEN_DRAIN in analogWrite

Author: Michael Kluge

cores/esp8266/Arduino.h

@@ -170,7 +170,7 @@ void digitalWrite(uint8_t pin, uint8_t val);
 int digitalRead(uint8_t pin);
 int analogRead(uint8_t pin);
 void analogReference(uint8_t mode);
-void analogWrite(uint8_t pin, int val);
+void analogWrite(uint8_t pin, int val, bool openDrain = false);
 void analogWriteFreq(uint32_t freq);
 void analogWriteResolution(int res);
 void analogWriteRange(uint32_t range);

cores/esp8266/core_esp8266_wiring_pwm.cpp

@@ -43,7 +43,7 @@ extern void __analogWriteFreq(uint32_t freq) {
   _setPWMFreq(freq);
 }
 
-extern void __analogWrite(uint8_t pin, int val) {
+extern void __analogWrite(uint8_t pin, int val, bool openDrain) {
   if (pin > 16) {
     return;
   }
@@ -62,7 +62,11 @@ extern void __analogWrite(uint8_t pin, int val) {
     analogMap &= ~(1 << pin);
   }
   else {
-    pinMode(pin, OUTPUT);
+    if(openDrain) {
+      pinMode(pin, OUTPUT_OPEN_DRAIN);
+    } else {
+      pinMode(pin, OUTPUT);
+    }
   }
   uint32_t high = (analogPeriod * val) / analogScale;
   uint32_t low = analogPeriod - high;
@@ -87,7 +91,7 @@ extern void __analogWriteResolution(int res) {
   }
 }
 
-extern void analogWrite(uint8_t pin, int val) __attribute__((weak, alias("__analogWrite")));
+extern void analogWrite(uint8_t pin, int val, bool openDrain) __attribute__((weak, alias("__analogWrite")));
 extern void analogWriteFreq(uint32_t freq) __attribute__((weak, alias("__analogWriteFreq")));
 extern void analogWriteRange(uint32_t range) __attribute__((weak, alias("__analogWriteRange")));
 extern void analogWriteResolution(int res) __attribute__((weak, alias("__analogWriteResolution")));