Add control of chip select pin

SerialFlash.h

 class SerialFlashChip
 {
 public:
-	static bool begin();
+	static bool begin(uint8_t pin = 6);
 	static uint32_t capacity(const uint8_t *id);
 	static uint32_t blockSize();
 	static void sleep();

SerialFlashChip.cpp

 #include "SerialFlash.h"
 #include "util/SerialFlash_directwrite.h"
 
-#define CSCONFIG()  pinMode(6, OUTPUT)
-#define CSASSERT()  digitalWriteFast(6, LOW)
-#define CSRELEASE() digitalWriteFast(6, HIGH)
+#define CSASSERT()  DIRECT_WRITE_LOW(cspin_basereg, cspin_bitmask)
+#define CSRELEASE() DIRECT_WRITE_HIGH(cspin_basereg, cspin_bitmask)
 #define SPICONFIG   SPISettings(50000000, MSBFIRST, SPI_MODE0)
 
-#if !defined(__arm__) || !defined(CORE_TEENSY)
-#define digitalWriteFast(pin, state) digitalWrite((pin), (state))
-#endif
-
 uint16_t SerialFlashChip::dirindex = 0;
 uint8_t SerialFlashChip::flags = 0;
 uint8_t SerialFlashChip::busy = 0;
 
+static volatile IO_REG_TYPE *cspin_basereg;
+static IO_REG_TYPE cspin_bitmask;
+
 #define FLAG_32BIT_ADDR		0x01	// larger than 16 MByte address
 #define FLAG_STATUS_CMD70	0x02	// requires special busy flag check
 #define FLAG_DIFF_SUSPEND	0x04	// uses 2 different suspend commands
 //#define FLAG_DIFF_SUSPEND	0x04	// uses 2 different suspend commands
 //#define FLAG_256K_BLOCKS	0x10	// has 256K erase blocks
 
-bool SerialFlashChip::begin()
+bool SerialFlashChip::begin(uint8_t pin)
 {
 	uint8_t id[3];
 	uint8_t f;
 	uint32_t size;
 
+	cspin_basereg = PIN_TO_BASEREG(pin);
+	cspin_bitmask = PIN_TO_BITMASK(pin);
 	SPI.begin();
-	CSCONFIG();
+	pinMode(pin, OUTPUT);
 	CSRELEASE();
 	readID(id);
 	f = 0;
 	return true;
 }
 
+// chips tested: https://github.com/PaulStoffregen/SerialFlash/pull/12#issuecomment-169596992
+//
 void SerialFlashChip::sleep()
 {
 	if (busy) wait();

examples/CopyFromSD/CopyFromSD.ino

 #include <SD.h>
 #include <SPI.h>
 
-const int SDchipSelect = 4; // Audio Shield has SD card CS on pin 10
-const int FlashChipSelect = 6;
+const int SDchipSelect = 4;    // Audio Shield has SD card CS on pin 10
+const int FlashChipSelect = 6; // digital pin for flash chip CS pin
 
 void setup() {
   //uncomment these if using Teensy audio shield
   if (!SD.begin(SDchipSelect)) {
     error("Unable to access SD card");
   }
-  if (!SerialFlash.begin()) {
+  if (!SerialFlash.begin(FlashChipSelect)) {
     error("Unable to access SPI Flash chip");
   }
 

examples/CopyFromSerial/CopyFromSerial.ino

 
 
 //SPI Pins (these are the values on the Audio board; change them if you have different ones)
-#define MOSI              7
+#define MOSI               7
 #define MISO              12
-#define SCK                14
+#define SCK               14
+#define CSPIN              6
 
 void setup(){
   Serial.begin(9600);  //Teensy serial is always at full USB speed and buffered... the baud rate here is required but ignored
   SPI.setMOSI(MOSI);
   SPI.setMISO(MISO);
   SPI.setSCK(SCK);
-  SerialFlash.begin();
+  SerialFlash.begin(CSPIN);
 
   //We start by formatting the flash...
   uint8_t id[3];

examples/EraseEverything/EraseEverything.ino

 #include <SerialFlash.h>
 #include <SPI.h>
 
+const int FlashChipSelect = 6; // digital pin for flash chip CS pin
+
 SerialFlashFile file;
 
 const unsigned long testIncrement = 4096;
   while (!Serial && (millis() - startMillis < 10000)) ;
   delay(100);
 
-  SerialFlash.begin();
+  SerialFlash.begin(FlashChipSelect);
   unsigned char id[3];
   SerialFlash.readID(id);
   unsigned long size = SerialFlash.capacity(id);

examples/ListFiles/ListFiles.ino

 #include <SerialFlash.h>
 #include <SPI.h>
 
-const int FlashChipSelect = 6;
+const int FlashChipSelect = 6; // digital pin for flash chip CS pin
 
 void setup() {
   //uncomment these if using Teensy audio shield
   delay(100);
   Serial.println("All Files on SPI Flash chip:");
 
-  if (!SerialFlash.begin()) {
+  if (!SerialFlash.begin(FlashChipSelect)) {
     error("Unable to access SPI Flash chip");
   }
 

examples/RawHardwareTest/RawHardwareTest.ino

 // the exact part number and manufacturer of the chip.
 
 
-
 #include <SerialFlash.h>
 #include <SPI.h>
 
+const int FlashChipSelect = 6; // digital pin for flash chip CS pin
+
 SerialFlashFile file;
 
 const unsigned long testIncrement = 4096;
   delay(100);
 
   Serial.println("Raw SerialFlash Hardware Test");
-  SerialFlash.begin();
+  SerialFlash.begin(FlashChipSelect);
 
   if (test()) {
     Serial.println();