Add option to set SPI frequency in SD.begin(...)

Author: sandeepmistry

src/SD.cpp

@@ -347,7 +347,12 @@ boolean SDClass::begin(uint8_t csPin) {
          root.openRoot(volume);
 }
 
-
+boolean SDClass::begin(uint32_t clock, uint8_t csPin) {
+  return card.init(SPI_HALF_SPEED, csPin) &&
+         card.setSpiClock(clock) &&
+         volume.init(card) &&
+         root.openRoot(volume);
+}
 
 // this little helper is used to traverse paths
 SdFile SDClass::getParentDir(const char *filepath, int *index) {

src/SD.h

@@ -68,6 +68,7 @@ class SDClass {
   // This needs to be called to set up the connection to the SD card
   // before other methods are used.
   boolean begin(uint8_t csPin = SD_CHIP_SELECT_PIN);
+  boolean begin(uint32_t clock, uint8_t csPin);
 
   // Open the specified file/directory with the supplied mode (e.g. read or
   // write, etc). Returns a File object for interacting with the file.

src/utility/Sd2Card.cpp

@@ -540,6 +540,15 @@ uint8_t Sd2Card::setSckRate(uint8_t sckRateID) {
 #endif // USE_SPI_LIB
   return true;
 }
+#ifdef USE_SPI_LIB
+//------------------------------------------------------------------------------
+// set the SPI clock frequency
+uint8_t Sd2Card::setSpiClock(uint32_t clock)
+{
+  settings = SPISettings(clock, MSBFIRST, SPI_MODE0);
+  return true;
+}
+#endif
 //------------------------------------------------------------------------------
 // wait for card to go not busy
 uint8_t Sd2Card::waitNotBusy(uint16_t timeoutMillis) {

src/utility/Sd2Card.h

@@ -223,6 +223,9 @@ class Sd2Card {
   }
   void readEnd(void);
   uint8_t setSckRate(uint8_t sckRateID);
+#ifdef USE_SPI_LIB
+  uint8_t setSpiClock(uint32_t clock);
+#endif
   /** Return the card type: SD V1, SD V2 or SDHC */
   uint8_t type(void) const {return type_;}
   uint8_t writeBlock(uint32_t blockNumber, const uint8_t* src);