Add rxFifoFull() function, Only flush tx w ack_plds

- Add function to check if the rx fifo has been filled and potentially
overloaded
- TX FIFO is now only flushed when transitioning between reading/writing
as start/stopListening() is called IF dynamic payloads are enabled

RF24.cpp

@@ -517,7 +517,9 @@ void RF24::startListening(void)
 
   // Flush buffers
   //flush_rx();
-  flush_tx();
+  if(read_register(FEATURE) & _BV(EN_ACK_PAY)){
+	flush_tx();
+  }
 
   // Go!
   ce(HIGH);
@@ -538,7 +540,9 @@ void RF24::stopListening(void)
   	delayMicroseconds(300);
   #endif
   delayMicroseconds(130);
-  flush_tx();
+  if(read_register(FEATURE) & _BV(EN_ACK_PAY)){
+	flush_tx();
+  }
   //flush_rx();
   write_register(CONFIG, ( read_register(CONFIG) ) & ~_BV(PRIM_RX) );
   write_register(EN_RXADDR,read_register(EN_RXADDR) | _BV(pgm_read_byte(&child_pipe_enable[0]))); // Enable RX on pipe0
@@ -714,6 +718,7 @@ void RF24::startFastWrite( const void* buf, uint8_t len, const bool multicast){
 
 }
 
+/****************************************************************************/
 
 //Added the original startWrite back in so users can still use interrupts, ack payloads, etc
 //Allows the library to pass all tests
@@ -732,6 +737,13 @@ void RF24::startWrite( const void* buf, uint8_t len, const bool multicast ){
 
 }
 
+/****************************************************************************/
+
+bool RF24::rxFifoFull(){
+	return read_register(FIFO_STATUS) & _BV(RX_FULL);
+}
+/****************************************************************************/
+
 bool RF24::txStandBy(){
     #if defined (FAILURE_HANDLING)
 		uint32_t timeout = millis();
@@ -755,6 +767,8 @@ bool RF24::txStandBy(){
 	return 1;
 }
 
+/****************************************************************************/
+
 bool RF24::txStandBy(uint32_t timeout){
 
 	uint32_t start = millis();

RF24.h

@@ -217,6 +217,12 @@ class RF24
    */
   bool available(uint8_t* pipe_num);
 
+  /**
+   * Check if the radio needs to be read. Can be used to prevent data loss
+   * @@return True if all three 32-byte radio buffers are full
+   */
+  bool rxFifoFull();
+
   /**
    * Enter low-power mode
    *
@@ -908,6 +914,7 @@ class RF24
    */
   uint8_t get_status(void);
 
+  #if !defined (MINIMAL)
   /**
    * Decode and print the given status to stdout
    *
@@ -951,7 +958,7 @@ class RF24
    * @param qty How many successive registers to print
    */
   void print_address_register(const char* name, uint8_t reg, uint8_t qty = 1);
-
+#endif
   /**
    * Turn on or off the special features of the chip
    *
@@ -1063,6 +1070,12 @@ class RF24
  * ping/pong cycle, and the receiver sleeps between payloads. <br>
  */
 
+ /**
+ * @example rf24ping85.ino
+ * <b>New: Contributed by https://github.com/tong67</b><br>
+ * This is an example of how to use the RF24 class to communicate with ATtiny85 and other node. <br>
+ */
+
 /**
  * @example pingpair_dyn.ino
  *

RPi/RF24/RF24.cpp

@@ -514,8 +514,10 @@ void RF24::startListening(void)
     closeReadingPipe(0);
   }
   // Flush buffers
-  //flush_rx();
-  flush_tx();
+  flush_rx();
+  if(read_register(FEATURE) & _BV(EN_ACK_PAY)){
+	flush_tx();
+  }
 
   // Go!
   bcm2835_gpio_write(ce_pin, HIGH);
@@ -535,8 +537,11 @@ void RF24::stopListening(void)
 {
   bcm2835_gpio_write(ce_pin, LOW);
   delayMicroseconds(470);
-  flush_tx();
-  //flush_rx();
+
+  if(read_register(FEATURE) & _BV(EN_ACK_PAY)){
+	flush_tx();
+  }
+  flush_rx();
 
   write_register(CONFIG, ( read_register(CONFIG) ) & ~_BV(PRIM_RX) );  
   write_register(EN_RXADDR,read_register(EN_RXADDR) | _BV(pgm_read_byte(&child_pipe_enable[0])));
@@ -743,7 +748,11 @@ bool RF24::txStandBy(){
 	bcm2835_gpio_write(ce_pin, LOW);			   //Set STANDBY-I mode
 	return 1;
 }
+bool RF24::rxFifoFull(){
 
+	bool val = (read_register(FIFO_STATUS) & _BV(RX_FULL));
+	return val;
+}
 /****************************************************************************/
 
 bool RF24::txStandBy(uint32_t timeout){

RPi/RF24/RF24.h

@@ -795,6 +795,12 @@ class RF24
    */
   bool available(uint8_t* pipe_num);
 
+  /**
+   * Check if the radio needs to be read. Can be used to prevent data loss and during delays
+   * @@return True if all three 32-byte radio buffers are full
+   */
+  bool rxFifoFull();
+
 /**
    * Non-blocking write to the open writing pipe used for buffered writes
    *