Add option to select SPI speed at SD::begin

Author: ficeto

libraries/SD/src/SD.cpp

@@ -332,15 +332,15 @@ boolean callback_rmdir(SdFile& parentDir, char *filePathComponent,
 
 
 
-boolean SDClass::begin(uint8_t csPin) {
+boolean SDClass::begin(uint8_t csPin, uint32_t speed) {
   /*
 
     Performs the initialisation required by the sdfatlib library.
 
     Return true if initialization succeeds, false otherwise.
 
    */
-  return card.init(SPI_HALF_SPEED, csPin) &&
+  return card.init(speed, csPin) &&
          volume.init(card) &&
          root.openRoot(volume);
 }

libraries/SD/src/SD.h

@@ -65,7 +65,7 @@ class SDClass {
 public:
   // 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(uint8_t csPin = SD_CHIP_SELECT_PIN, uint32_t speed = SPI_HALF_SPEED);
 
   // Open the specified file/directory with the supplied mode (e.g. read or
   // write, etc). Returns a File object for interacting with the file.