Reorganize RX message buffering checks

- fix doxygen warning

drivers/RF24/RF24.cpp

@@ -25,7 +25,7 @@
 LOCAL uint8_t MY_RF24_BASE_ADDR[MY_RF24_ADDR_WIDTH] = { MY_RF24_BASE_RADIO_ID };
 LOCAL uint8_t MY_RF24_NODE_ADDRESS = AUTO;
 
-#ifdef MY_RF24_IRQ_PIN
+#if defined(MY_RX_MESSAGE_BUFFER_FEATURE)
 	LOCAL RF24_receiveCallbackType RF24_receiveCallback = NULL;
 #endif
 
@@ -261,7 +261,7 @@ LOCAL bool RF24_sanityCheck(void) {
 	return status;
 }
 
-#ifdef MY_RF24_IRQ_PIN
+#if defined(MY_RX_MESSAGE_BUFFER_FEATURE)
 LOCAL void RF24_irqHandler( void )
 {
 	if (RF24_receiveCallback)
@@ -307,14 +307,14 @@ LOCAL bool RF24_initialize(void) {
 	// Initialize pins
 	pinMode(MY_RF24_CE_PIN,OUTPUT);
 	pinMode(MY_RF24_CS_PIN,OUTPUT);
-	#ifdef MY_RF24_IRQ_PIN
+	#if defined(MY_RX_MESSAGE_BUFFER_FEATURE)
 		pinMode(MY_RF24_IRQ_PIN,INPUT);
 	#endif
 	// Initialize SPI
 	_SPI.begin();
 	RF24_ce(LOW);
 	RF24_csn(HIGH);
-	#ifdef MY_RF24_IRQ_PIN
+	#if defined(MY_RX_MESSAGE_BUFFER_FEATURE)
 		// assure SPI can be used from interrupt context
 		// Note: ESP8266 & SoftSPI currently do not support interrupt usage for SPI,
 		// therefore it is unsafe to use MY_RF24_IRQ_PIN with ESP8266/SoftSPI!

drivers/RF24/RF24.h

@@ -36,9 +36,6 @@
 #if defined (ARDUINO) && !defined (__arm__) && !defined (_SPI)
 	#if defined(MY_SOFTSPI)
 		SoftSPI<MY_SOFT_SPI_MISO_PIN, MY_SOFT_SPI_MOSI_PIN, MY_SOFT_SPI_SCK_PIN, MY_RF24_SPI_DATA_MODE> _SPI;
-	#elif defined(ARDUINO_ARCH_SAMD)
-		#include <SPI.h>
-		#define _SPI SPI1
 	#else	    
 		#include <SPI.h>
 		#define _SPI SPI
@@ -61,8 +58,31 @@
 	#endif
 #endif
 
+// verify RF24 IRQ defs
+#if defined(MY_RX_MESSAGE_BUFFER_FEATURE)
+	#if !defined(MY_RF24_IRQ_PIN)
+		#error Message buffering feature requires MY_RF24_IRQ_PIN to be defined!
+	#endif
+	// SoftSPI does not support usingInterrupt()
+	#ifdef MY_SOFTSPI
+		#error RF24 IRQ usage cannot be used with Soft SPI
+	#endif
+	// ESP8266 does not support usingInterrupt()
+	#ifdef ARDUINO_ARCH_ESP8266
+		#error RF24 IRQ usage cannot be used with ESP8266
+	#endif
+	#ifndef SPI_HAS_TRANSACTION
+		#error RF24 IRQ usage requires transactional SPI support
+	#endif
+#else
+	#ifdef MY_RX_MESSAGE_BUFFER_SIZE
+		#error Receive message buffering requires RF24 IRQ usage
+	#endif
+#endif
+
+
 // RF24 settings
-#ifdef MY_RF24_IRQ_PIN
+#if defined(MY_RX_MESSAGE_BUFFER_FEATURE)
 	#define MY_RF24_CONFIGURATION (uint8_t) ((RF24_CRC_16 << 2) | (1 << MASK_TX_DS) | (1 << MASK_MAX_RT))
 #else
 	#define MY_RF24_CONFIGURATION (uint8_t) (RF24_CRC_16 << 2)
@@ -253,7 +273,7 @@ LOCAL void RF24_setPipeLSB(uint8_t pipe, uint8_t LSB);
 LOCAL void RF24_setStatus(uint8_t status);
 LOCAL void RF24_enableFeatures(void);
 
-#ifdef MY_RF24_IRQ_PIN
+#if defined(MY_RX_MESSAGE_BUFFER_FEATURE)
 	typedef void (*RF24_receiveCallbackType)(void);
   /**
 	 * Register a callback, which will be called (from interrupt context) for every message received.