nRF24L01+ Running on Maple

Last weekend, I got a Maple Native board from Leaf Labs. This is a somewhat-Arduino-compatible board running a STM Cortex-M3 processor with 512k flash and 1M of external RAM. I figure it will ease the wait for the Arduino Due.

So my first task is to port RF24, my Driver for nRF24L01(+) 2.4GHz Wireless Transceiver library. This library makes it easy to use dirt-cheap nRF24L01+ modules for radio communication.

It turns out the port was dead simple. So now Maple users can enjoy the benefits of $4 RF Radios.

The Hardware

In the picture above, I re-used the board introduced earlier in my Getting Started with nRF24L01+ on Arduino post. Happily, the pins are in the same order on the Arduino as the Maple, so the same board fits neatly onto the Maple Native, albeit oriented backwards. Then, wires are needed to connect VCC and GND over to the module. All of the other power (red & black) wires on the green board are extraneous on Maple.

The Example

Check out the specific example for Maple, pingpair_maple.

Put the same sketch on two units. On one of the boards, tie pin #10 to ground. On the other, leave it floating. This mechanism identifies one of the units as the sender, and the other as the receiver. Power them both up, and watch the debug spew tell the tale.

Now sending 90...ok...Got response 90, round-trip delay: 28
Now sending 1122...ok...Got response 1122, round-trip delay: 26
Now sending 2152...ok...Got response 2152, round-trip delay: 27
Now sending 3182...ok...Got response 3182, round-trip delay: 29
Now sending 4214...ok...Got response 4214, round-trip delay: 27
Now sending 5244...ok...Got response 5244, round-trip delay: 29
Now sending 6277...ok...Got response 6277, round-trip delay: 26
Now sending 7307...ok...Got response 7307, round-trip delay: 26
Now sending 8337...ok...Got response 8337, round-trip delay: 29
Now sending 9369...ok...Got response 9369, round-trip delay: 27
Now sending 10399...ok...Got response 10399, round-trip delay: 29
Now sending 11431...ok...Got response 11431, round-trip delay: 27
Now sending 12462...ok...Got response 12462, round-trip delay: 28


As I only have one Maple, I tested it using a Maple and one of my Wireless Sensor Nodes

The Changes

Mainly what was needed was to re-arrange the Arduino-specific header files into their own header, and add some compatibility glue.

rf24_config.h

#ifndef __RF24_CONFIG_H__
#define __RF24_CONFIG_H__
 
#if ARDUINO < 100
#include <WProgram.h>
#else
#include <Arduino.h>
#endif
 
#include <stddef.h>
 
// Stuff that is normally provided by Arduino
#ifndef ARDUINO
#include <stdint.h>
#include <stdio.h>
#include <string.h>
extern HardwareSPI SPI;
#define _BV(x) (1<<(x))
#endif
 
#undef SERIAL_DEBUG
#ifdef SERIAL_DEBUG
#define IF_SERIAL_DEBUG(x) ({x;})
#else
#define IF_SERIAL_DEBUG(x)
#endif
 
// Avoid spurious warnings
#if ! defined( NATIVE ) && defined( ARDUINO )
#undef PROGMEM
#define PROGMEM __attribute__(( section(".progmem.data") ))
#undef PSTR
#define PSTR(s) (__extension__({static prog_char __c[] PROGMEM = (s); &__c[0];}))
#endif
 
// Progmem is Arduino-specific
#ifdef ARDUINO
#include <avr/pgmspace.h>
#define PRIPSTR "%S"
#else
typedef char const prog_char;
typedef uint16_t prog_uint16_t;
#define PSTR(x) (x)
#define printf_P printf
#define strlen_P strlen
#define PROGMEM
#define pgm_read_word(p) (*(p))
#define PRIPSTR "%s"
#endif
 
#endif // __RF24_CONFIG_H__


SPI Configiration

Needed to avoid setting SPI parameters in the Arduino fashion. Fortunately, the defaults for Maple HardwareSPI were correct for this radio, so no SPI configuration was needed whatsoever.

void RF24::csn(int mode)
{
#ifdef ARDUINO
SPI.setBitOrder(MSBFIRST);
SPI.setDataMode(SPI_MODE0);
SPI.setClockDivider(SPI_CLOCK_DIV4);
#endif
digitalWrite(csn_pin,mode);
}


pingpair_maple.pde

The example needed a little tuning:

//
// Maple specific setup. Other than this section, the sketch is the same on Maple as on
// Arduino
//
 
#ifdef MAPLE_IDE
 
// External startup function
extern void board_start(const char* program_name);
 
// Use SPI #2.
HardwareSPI SPI(2);
 
#else
#define board_startup printf
#define toggleLED(x) (x)
#endif