Adds support for also running on NRF52 targets (#291)

* Fix problem of transitions getting faster with each call of setTargetFPS

    On my app I noticed that each time I called setTargetFPS the transitions
    would become faster and faster, until finally they don't even take one
    frame.  The problem was that the FP math for calculating changeRatio
    would (because of rounding err) keep shrinking the number of ticksPerFrame.

    This change instead computs ticksPerFrame/perTransition based on the
    requested display time, so error can't accumulate from a series of calls.

    (In my app I only bump up target FPS before each transition but then
    I lower it down again afterwards to save CPU)

* Allow this library to work on other Arduinos (NRF52) besides ESPs

* Let users specify -1 for scl/sda to mean 'use current value'
(Also makes it easier to share code when users of library are targeting
multiple platforms)

* fix missing dependency, std::max is defined in algorithm

Author: geeksville

library.json

@@ -23,6 +23,7 @@
   "frameworks": "arduino",
   "platforms": [
     "espressif8266",
-    "espressif32"
+    "espressif32",
+    "nordicnrf52"
   ]
 }

src/SSD1306Wire.h

@@ -33,6 +33,7 @@
 
 #include "OLEDDisplay.h"
 #include <Wire.h>
+#include <algorithm>
 
 #if defined(ARDUINO_ARCH_AVR) || defined(ARDUINO_ARCH_STM32)
 #define _min	min
@@ -42,12 +43,12 @@
 class SSD1306Wire : public OLEDDisplay {
   private:
       uint8_t             _address;
-      uint8_t             _sda;
-      uint8_t             _scl;
+      int                 _sda;
+      int                 _scl;
       bool                _doI2cAutoInit = false;
 
   public:
-    SSD1306Wire(uint8_t _address, uint8_t _sda, uint8_t _scl, OLEDDISPLAY_GEOMETRY g = GEOMETRY_128_64) {
+    SSD1306Wire(uint8_t _address, int _sda = -1, int _scl = -1, OLEDDISPLAY_GEOMETRY g = GEOMETRY_128_64) {
       setGeometry(g);
 
       this->_address = _address;
@@ -56,10 +57,12 @@ class SSD1306Wire : public OLEDDisplay {
     }
 
     bool connect() {
-#ifdef ARDUINO_ARCH_AVR 
+#if !defined(ARDUINO_ARCH_ESP32) && !defined(ARDUINO_ARCH8266)
       Wire.begin();
 #else
-      Wire.begin(this->_sda, this->_scl);
+      // On ESP32 arduino, -1 means 'don't change pins', someone else has called begin for us.
+      if(this->_sda != -1)
+        Wire.begin(this->_sda, this->_scl);
 #endif
       // Let's use ~700khz if ESP8266 is in 160Mhz mode
       // this will be limited to ~400khz if the ESP8266 in 80Mhz mode.
@@ -84,10 +87,10 @@ class SSD1306Wire : public OLEDDisplay {
           for (x = 0; x < this->width(); x++) {
            uint16_t pos = x + y * this->width();
            if (buffer[pos] != buffer_back[pos]) {
-             minBoundY = _min(minBoundY, y);
-             maxBoundY = _max(maxBoundY, y);
-             minBoundX = _min(minBoundX, x);
-             maxBoundX = _max(maxBoundX, x);
+             minBoundY = std::min(minBoundY, y);
+             maxBoundY = std::max(maxBoundY, y);
+             minBoundX = std::min(minBoundX, x);
+             maxBoundX = std::max(maxBoundX, x);
            }
            buffer_back[pos] = buffer[pos];
          }
@@ -175,7 +178,7 @@ class SSD1306Wire : public OLEDDisplay {
 
     void initI2cIfNeccesary() {
       if (_doI2cAutoInit) {
-#ifdef ARDUINO_ARCH_AVR 
+#if !defined(ARDUINO_ARCH_ESP32) && !defined(ARDUINO_ARCH8266)
       	Wire.begin();
 #else
       	Wire.begin(this->_sda, this->_scl);