allow to set pin to OUTPUT_OPEN_DRAIN in analogWriteMode (#7841)

* allow to set pin to OUTPUT_OPEN_DRAIN in analogWrite

* remove parameter with default value

* Update core_esp8266_wiring_pwm.cpp

* update documentation accordingly

Author: klugem

cores/esp8266/Arduino.h

@@ -171,6 +171,7 @@ int digitalRead(uint8_t pin);
 int analogRead(uint8_t pin);
 void analogReference(uint8_t mode);
 void analogWrite(uint8_t pin, int val);
+void analogWriteMode(uint8_t pin, int val, bool openDrain);
 void analogWriteFreq(uint32_t freq);
 void analogWriteResolution(int res);
 void analogWriteRange(uint32_t range);

cores/esp8266/core_esp8266_wiring_pwm.cpp

@@ -44,6 +44,10 @@ extern void __analogWriteFreq(uint32_t freq) {
 }
 
 extern void __analogWrite(uint8_t pin, int val) {
+  analogWriteMode(pin, val, false);
+}
+
+extern void __analogWriteMode(uint8_t pin, int val, bool openDrain) {
   if (pin > 16) {
     return;
   }
@@ -62,7 +66,11 @@ 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;
@@ -88,6 +96,7 @@ extern void __analogWriteResolution(int res) {
 }
 
 extern void analogWrite(uint8_t pin, int val) __attribute__((weak, alias("__analogWrite")));
+extern void analogWriteMode(uint8_t pin, int val, bool openDrain) __attribute__((weak, alias("__analogWriteMode")));
 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")));

doc/reference.rst

@@ -109,6 +109,9 @@ PWM range may be changed by calling ``analogWriteRange(new_range)`` or
 ``analogWriteResolution(bits)``.  ``new_range`` may be from 15...65535
 or ``bits`` may be from 4...16.
 
+The function ``analogWriteMode(pin, value, openDrain)`` allows to sets
+the pin mode to ``OUTPUT_OPEN_DRAIN`` instead of ``OUTPUT``.
+
 **NOTE:** The default ``analogWrite`` range was 1023 in releases before
 3.0, but this lead to incompatibility with external libraries which
 depended on the Arduino core default of 256.  Existing applications which