Hardware SPI BREAKING: unswap mode 2 and 3 for portability

use SPI.restoreEsp8266LegacyMode2And3() for former behaviour

Author: d-a-v

libraries/SPI/SPI.cpp

@@ -42,6 +42,7 @@ typedef union {
 SPIClass::SPIClass() {
     useHwCs = false;
     pinSet = SPI_PINS_HSPI;
+    legacyMode2and3 = false;
 }
 
 bool SPIClass::pins(int8_t sck, int8_t miso, int8_t mosi, int8_t ss)
@@ -161,6 +162,13 @@ void SPIClass::setDataMode(uint8_t dataMode) {
     bool CPOL = (dataMode & 0x10); ///< CPOL (Clock Polarity)
     bool CPHA = (dataMode & 0x01); ///< CPHA (Clock Phase)
 
+    if(!legacyMode2and3) {
+        // https://github.com/esp8266/Arduino/issues/2416
+        // https://github.com/esp8266/Arduino/pull/2418
+        if(CPOL)          // Ensure same behavior as
+            CPHA ^= 1;    // SAM, AVR and Intel Boards
+    }
+
     if(CPHA) {
         SPI1U |= (SPIUSME);
     } else {

libraries/SPI/SPI.h

@@ -58,6 +58,7 @@ class SPIClass {
   void end();
   void setHwCs(bool use);
   void setBitOrder(uint8_t bitOrder);  
+  void restoreEsp8266LegacyMode2And3(); // must be called *before* setDataMode()
   void setDataMode(uint8_t dataMode);
   void setFrequency(uint32_t freq);
   void setClockDivider(uint32_t clockDiv);
@@ -77,6 +78,7 @@ class SPIClass {
 private:
   bool useHwCs;
   uint8_t pinSet;
+  bool legacyMode2and3;
   void writeBytes_(const uint8_t * data, uint8_t size);
   void transferBytes_(const uint8_t * out, uint8_t * in, uint8_t size);
   void transferBytesAligned_(const uint8_t * out, uint8_t * in, uint8_t size);