Raspberry Pi support

Added support for hardware SPI on RPI per jscrane fork:
- Fixed a few bugs with single SPI transfers
- Aligned with optimized RF24 library fork
- Updated bmc2835 files per
http://www.airspayce.com/mikem/bcm2835/index.html
- Merged bcm files with changes from
https://github.com/farconada/RF24Network
- Added example files
- Added setup info to readme

RPi/RF24/examples/transfer.cpp

@@ -0,0 +1,148 @@
+/*
+TMRh20 2014
+
+ This program is free software; you can redistribute it and/or
+ modify it under the terms of the GNU General Public License
+ version 2 as published by the Free Software Foundation.
+ */
+
+/** General Data Transfer Rate Test
+ * This example demonstrates basic data transfer functionality with the 
+ updated library. This example will display the transfer rates acheived using
+ the slower form of high-speed transfer using blocking-writes.
+ */
+
+#include <cstdlib>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include "./RF24.h"
+
+
+using namespace std;
+//
+// Hardware configuration
+//
+
+// CE Pin, CSN Pin, SPI Speed
+
+// Setup for GPIO 22 CE and GPIO 25 CSN with SPI Speed @ 1Mhz
+//RF24 radio(RPI_V2_GPIO_P1_22, RPI_V2_GPIO_P1_18, BCM2835_SPI_SPEED_1MHZ);
+
+// Setup for GPIO 22 CE and CE0 CSN with SPI Speed @ 4Mhz
+//RF24 radio(RPI_V2_GPIO_P1_15, BCM2835_SPI_CS0, BCM2835_SPI_SPEED_4MHZ); 
+
+// Setup for GPIO 22 CE and CE1 CSN with SPI Speed @ 8Mhz
+RF24 radio(RPI_V2_GPIO_P1_15, RPI_V2_GPIO_P1_26, BCM2835_SPI_SPEED_8MHZ);  
+
+
+
+// Radio pipe addresses for the 2 nodes to communicate.
+const uint64_t addresses[2] = { 0xABCDABCD71LL, 0x544d52687CLL };
+
+bool role_ping_out = 1, role_pong_back = 0;
+bool role = 0;
+uint8_t data[32]; 
+unsigned long startTime, stopTime, counter, rxTimer=0; 
+
+int main(int argc, char** argv){
+
+ 
+  // Print preamble:
+
+  printf("RF24/examples/Transfer/\n");
+  
+  radio.begin();                           // Setup and configure rf radio
+  radio.setChannel(1);
+  radio.setPALevel(RF24_PA_MAX);
+  radio.setDataRate(RF24_2MBPS);
+  radio.setAutoAck(1);                     // Ensure autoACK is enabled
+  radio.setRetries(2,15);                   // Optionally, increase the delay between retries & # of retries
+  radio.setCRCLength(RF24_CRC_8);
+  radio.printDetails();
+/********* Role chooser ***********/
+
+  printf("\n ************ Role Setup ***********\n");
+  string input = "";
+  char myChar = {0};
+  cout << "Choose a role: Enter 0 for receiver, 1 for transmitter (CTRL+C to exit)\n>";
+  getline(cin,input);
+  
+  if(input.length() == 1) {
+	myChar = input[0];
+	if(myChar == '0'){
+		cout << "Role: Pong Back, awaiting transmission " << endl << endl;
+	}else{  cout << "Role: Ping Out, starting transmission " << endl << endl;
+		role = role_ping_out;
+	}
+  }
+/***********************************/
+
+    if ( role == role_ping_out )    {
+      radio.openWritingPipe(addresses[0]);
+      radio.openReadingPipe(1,addresses[1]);
+    } else {
+      radio.openWritingPipe(addresses[1]);
+      radio.openReadingPipe(1,addresses[0]);
+      radio.startListening();
+    }
+    
+     
+  for(int i=0; i<32; i++){
+     data[i] = rand() % 255;               //Load the buffer with random data
+  }
+
+    // forever loop
+    while (1){
+
+	if (role == role_ping_out){
+		sleep(2);
+		printf("Initiating Basic Data Transfer\n\r");
+
+		long int cycles = 10000; //Change this to a higher or lower number.
+
+		startTime = millis();
+
+		for(int i=0; i<cycles; i++){        //Loop through a number of cycles
+      			data[0] = i;                      //Change the first byte of the payload for identification
+      			if(!radio.writeFast(&data,32)){   //Write to the FIFO buffers        
+        			counter++;                      //Keep count of failed payloads
+      			}
+    		}
+		stopTime = millis();
+
+		if(!radio.txStandBy()){ counter+=3; }
+
+  		float numBytes = cycles*32;
+   		float rate = numBytes / (stopTime - startTime);
+    
+  		printf("Transfer complete at %.2f KB/s \n\r",rate);
+   		printf("%lu of %lu Packets Failed to Send\n\r",counter,cycles);
+  		counter = 0;   
+
+	}
+    
+
+if(role == role_pong_back){
+     while(radio.available()){       
+      radio.read(&data,32);
+      counter++;
+     }
+   if(millis() - rxTimer > 1000){
+     rxTimer = millis();
+     printf("Rate: ");
+     float numBytes = counter*32;
+     printf("%.2f KB/s \n\r",numBytes/1000);
+     printf("Payload Count: %lu \n\r", counter);
+     counter = 0;
+   }
+  }
+
+} // loop
+} // main
+
+
+
+
+
+