Created example program showing usage of both VSPI/HSPI within arduino API (#1368)

libraries/SPI/examples/SPI_Multiple_Buses/SPI_Multiple_Buses.ino

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+
+
+/* The ESP32 has four SPi buses, however as of right now only two of
+ * them are available to use, HSPI and VSPI. Simply using the SPI API 
+ * as illustrated in Arduino examples will use HSPI, leaving VSPI unused.
+ * 
+ * However if we simply intialise two instance of the SPI class for both
+ * of these buses both can be used. However when just using these the Arduino
+ * way only will actually be outputting at a time.
+ * 
+ * Logic analyser capture is in the same folder as this example as
+ * "multiple_bus_output.png"
+ * 
+ * created 30/04/2018 by Alistair Symonds
+ */
+#include <SPI.h>
+
+static const int spiClk = 1000000; // 1 MHz
+
+//uninitalised pointers to SPI objects
+SPIClass * vspi = NULL;
+SPIClass * hspi = NULL;
+
+void setup() {
+  //initialise two instances of the SPIClass attached to VSPI and HSPI respectively
+  vspi = new SPIClass(VSPI);
+  hspi = new SPIClass(HSPI);
+  
+  //clock miso mosi ss
+
+  //initialise vspi with default pins
+  //SCLK = 18, MISO = 19, MOSI = 23, SS = 5
+  vspi->begin();
+  //alternatively route through GPIO pins of your choice
+  //hspi->begin(5,6,7,8); //SCLK, MISO, MOSI, SS
+  
+  //initialise hspi with default pins
+  //SCLK = 14, MISO = 12, MOSI = 13, SS = 15
+  hspi->begin(); 
+  //alternatively route through GPIO pins
+  //hspi->begin(1,2,3,4); //SCLK, MISO, MOSI, SS
+
+  //set up slave select pins as outputs as the Arduino API
+  //doesn't handle automatically pulling SS low
+  pinMode(5, OUTPUT); //VSPI SS
+  pinMode(15, OUTPUT); //HSPI SS
+
+}
+
+// the loop function runs over and over again until power down or reset
+void loop() {
+  //use the SPI buses
+  vspiCommand();
+  hspiCommand();
+  delay(100);
+}
+
+void vspiCommand() {
+  byte data = 0b01010101; // junk data to illustrate usage
+
+  //use it as you would the regular arduino SPI API
+  vspi->beginTransaction(SPISettings(spiClk, MSBFIRST, SPI_MODE0));
+  digitalWrite(5, LOW); //pull SS slow to prep other end for transfer
+  vspi->transfer(data);  
+  digitalWrite(5, HIGH); //pull ss high to signify end of data transfer
+  vspi->endTransaction();
+}
+
+void hspiCommand() {
+  byte stuff = 0b11001100;
+  
+  hspi->beginTransaction(SPISettings(spiClk, MSBFIRST, SPI_MODE0));
+  digitalWrite(15, LOW);
+  hspi->transfer(stuff);
+  digitalWrite(15, HIGH);
+  hspi->endTransaction();
+}