Issue with Arduino Mega board (and probably others ?)

Tested RH_NRF24 with Arduino Maga. The documentation says

/// For an Arduino Mega:
/// \code
///                 Mega         Sparkfun WRL-00691
///                 5V-----------VCC   (3.3V to 7V in)
///             pin D8-----------CE    (chip enable in)
///          SS pin D53----------CSN   (chip select in)
///         SCK pin D52----------SCK   (SPI clock in)
///        MOSI pin D51----------SDI   (SPI Data in)
///        MISO pin D50----------SDO   (SPI data out)
///                              IRQ   (Interrupt output, not connected)
///                 GND----------GND   (ground in)
/// \endcode
/// and you can then use the constructor RH_NRF24(8, 53).

But that does not work, as the file RadioHead.h sets "SS" in an incorrect way. In the Arduino pins_arduino.h file you find (for the Mega)

#define PIN_SPI_SS    (53)
#define PIN_SPI_MOSI  (51)
#define PIN_SPI_MISO  (50)
#define PIN_SPI_SCK   (52)

static const uint8_t SS   = PIN_SPI_SS;
static const uint8_t MOSI = PIN_SPI_MOSI;
static const uint8_t MISO = PIN_SPI_MISO;
static const uint8_t SCK  = PIN_SPI_SCK;

So SS is a static const of type uint8_t !!! In the file RadioHead.h SS is set with "#define", and you find

// Slave select pin, some platforms such as ATTiny do not define it.
#ifndef SS
 #define SS 10
#endif

As a result, for the Mega, SS is defined as pin 10 :-( :-(

You can easily test this. A simple sketch

#include <SPI.h>
void setup() {
  Serial.begin(115200);
  Serial.println(SS);
}
void loop() {
}

shows correctly 53 on the Serial monitor, while

#include <RH_NRF24.h>
#include <SPI.h>
void setup() {
  Serial.begin(115200);
  Serial.println(SS);
}
void loop() {
}

shows 10 ! :-(

Work around : use pin 10 for SS and initialize as RH_NRF24 nrf24(8, 10);

PaulStoffregen / RadioHead

Issue with Arduino Mega board (and probably others ?) #39