PIC32MX: High-speed Wireless Communication

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Original Assignment

Do not erase this section!

Your assignment is to create the circuit and code that allows two PIC32s to use wireless communication at high speeds using the Transceiver nRF24L01+ Module with Chip Antenna from Sparkfun.

Read up on the nRF24L01+ Module commands and create functions to allow a PIC32 to initialize and send and receive data.

Test your code by sending 1000 bytes of data from one PIC32 to the other and echo the data back. How long does this transmission take? How far can you separate the PIC32s before the transmission is unreliable?

Overview

This wiki describes how to wire a nRF24L01+ chip ("wireless chip") to the transmitting PIC32 board ("transmitter") and receiving PIC32 board ("receiver"), and includes annotated code describing the functions that facilitate the wireless communication.

To operate the system, you must properly connect the wireless chips to the PIC32s, load the transmitter code onto the PIC that you wish to act as a transmitter, load the receiver code onto the PIC that you wish to act as a receiver, properly connect an RS232 cable to the PIC and open a serial communication program (e.g. HyperTerminal or putty), and turn the NU32 boards on. If the system works, the transmitting PIC will broadcast any characters received from the PC via RS232, and the receiving PIC will display what it receives from wireless link on the PC via RS232. The payload width can be adjusted using the "[" and "]" keys on both the transmitting and receiving PICs. Both wireless chips must be set to the same payload width in order to communicate. Payload widths may vary from 1 to 32. The transmitting PIC will not transmit until enough characters have been entered to fill a payload. Once enough characters have been entered into the transmitting PIC, the serial display will move to a new line to signal transmission.

Circuit

Schematic of the nRF24L01+ connected to the PIC32_NU32 board

The wireless chip has 8 pins that need to be wired to the PIC:

(1) Vcc -> +3.3 Vdc supply
(2) CE -> uC pin PORTC.1, configured as GPIO/input
(3) CSN -> uC pin PORTC.2, configured as GPIO/output
(4) SCK -> uC pin PORTC.3/SCK, configured as SCK(SPI)/output
(5) MOSI -> uC pin PORTC.5/SDO, configured as SDO(SPI)/output
(6) MISO -> uC pin PORTC.4/SDI, configured as SDI(SPI)/input
(7) IRQ -> uC pin PORTB.0, configured as GPIO/input
(8) GND -> common digital ground

The +3.3V and ground are provided by the NU32 board. The term "uC" above stands for microcontroller, which is the PIC32 in our case. GPIO stands for General Purpose Input/Output.

Descriptions of the wireless chip's pins can be found in Brennan Ball's DIYembedded Tutorial 0. The SCK, MOSI, and MISO pins interface with the SPI on the PIC32 which allows for communication between the PIC and the wireless chip. The GPIO pins will be initialized as digital inputs or outputs in the code to enable/disable the wireless chip and check the wireless data transfer/receive stats.

In order to print information from the PIC to the PC, we need to wire an PIC_RS232 cable's transfer and receive lines to the UART ports of the NU32 board (F4, F5).

Code

Besides the main C files for the transmitter and receiver, the project also needs the nRF24L01.h header file and C file in addition to the hardware header and linker files. Download the nRF24L01+ header files.

Transmitter Code

 
// ************************************************************** 
 /*
 
 	WirelessTransmitter.c
 	Lab 5: High-speed Wireless Communication
 	Jonathan Drake, Caitlin Ramsey 
 	2010-02-16
 
 	This code initializes the nRF24L01+ chip as a transmitter and
 	continuously transmits a character every 100ms. The loop contains
 	code to both output the program's status to the PC via RS232
 	cable and onboard LEDs. 
 
 */ 
 // **************************************************************
 
 
 // Includes
 #include "HardwareProfile.h"
 #include "nrf24l01.h" 
 
 // Function Declarations
 // Note: Descriptions of functions found after main() function
 void Initialize(void);
 void InitializeIO(void);
 void SpiInitDevice(int chn, int isMaster, int frmEn, int frmMaster);
 void initUART2(int pbClk);
 unsigned char spi_send_read_byte(unsigned char byte);
 void Delayms( unsigned t);
 void Delayus( unsigned t);
 void Delaytus( unsigned t);
 
 // Constants
 #define DESIRED_BAUDRATE    	(19200)      // The desired BaudRate for RS232 communication w/ UART
 
 // Main Function
 int main(void) { 
 
 	 Initialize(); // initialize onboard LEDs, IO pins, UART2, SPI1, set up nRF24L01+ as TX
 
 	 char RS232_Out_Buffer[64]; // buffer for printing data to the screen via UART
 	 unsigned char data = 'x'; // char to be transmitted
  
 	 // print char to screen
 	 sprintf(RS232_Out_Buffer, "data to send = %c\r\n", data); 
 	 putsUART2(RS232_Out_Buffer);
 
 	 while(1)
 	 {
 		 putsUART2("...\r");	// print ... to show transmission
 		 nrf24l01_irq_clear_all(); //clear all interrupts in the 24L01
 		 nrf24l01_set_as_tx(); // force 24L01 to be a transmitter (this is a double-check)
  
 		 //transmit received char over RF, length = 1 byte, true = send away
 		 nrf24l01_write_tx_payload(&data, 1, true); 
 		 
 		 // is the 24L01 activated?
 		 if (nrf24l01_irq_pin_active()) {
 			 mLED_1_On();
  		 } else {
  			 mLED_1_Off();
  		 }
 		 
 		 // is the 24L01 an active transmitter?
 		 if (nrf24l01_irq_tx_ds_active()) {
 			 mLED_2_On();
 		 } else {
 			 mLED_2_Off();
 		 }			
 		 
 		 // wait until the packet has been sent or the maximum number of retries has been reached
 		 while(!(nrf24l01_irq_pin_active() && nrf24l01_irq_tx_ds_active()));	
 			 
 		 // toggle onboard LED 3 to indicate loop iterating
 		 mLED_3_Toggle();
 		 Delayms(100);	
 	 }
  
 } 
 
 // Initialize all initialize functions (function descriptions to follow)
 void Initialize(void) {
    
   	 // initialize peripheral bus clock to SYS_FREQ (80 MHz)    
  	 int	pbClk;
  	 pbClk = SYSTEMConfigPerformance(SYS_FREQ);
    	 
  	 // initialize UART   
  	 initUART2(pbClk);	
     	 
     // initialize input/output pins     
   	 InitializeIO();
      
  	 // initialize the SPI channel 1 as master, no frame mode   
  	 SpiInitDevice(1, 1, 0, 0);	   
        	 
  	 //initialize 24L01 to debug configuration as transfer, 1 byte data size, and auto-acknowledge mode disabled   
   	 nrf24l01_initialize_debug(false, 1, false);   
           	 
     // initialize all onboard LEDs on NU32   
  	 mInitAllLEDs();    
      
  	 // if program initialized correctly, indicate on PC & onboard LEDs     
  	 putsUART2("\r\n***** System Initialized *****\r\n");    
  	 mLED_0_On();   
       
 }
 
 // initialize IO pins
 void InitializeIO(void) {	
   	 TRISBbits.TRISB0 = 1; // set IRQ pin as input
  	 TRISC = 0xFFF9; // make CSN, CE digital outputs
  	 PORTC = 0x0004; // set CSN bit active
 }	
 
 
 // initialize UART2
 void initUART2(int pbClk) {
  	 #define config1 	UART_EN | UART_IDLE_CON | UART_RX_TX | UART_DIS_WAKE | UART_DIS_LOOPBACK | UART_DIS_ABAUD | UART_NO_PAR_8BIT | UART_1STOPBIT | UART_IRDA_DIS | UART_DIS_BCLK_CTS_RTS| UART_NORMAL_RX | UART_BRGH_SIXTEEN
  	 #define config2		UART_TX_PIN_LOW | UART_RX_ENABLE | UART_TX_ENABLE | UART_INT_TX | UART_INT_RX_CHAR | UART_ADR_DETECT_DIS | UART_RX_OVERRUN_CLEAR	
   	 OpenUART2( config1, config2, pbClk/16/DESIRED_BAUDRATE-1);	// calculate actual BAUD generate value.
   	 ConfigIntUART2(UART_INT_PR2 | UART_RX_INT_EN);
 }
 
 
 // initialize SPI
 void SpiInitDevice(int chn, int isMaster, int frmEn, int frmMaster) {
   	 unsigned int config = SPI_CON_MODE16|SPI_CON_SMP|SPI_CON_ON;	// SPI configuration word
   	 if(isMaster)
   	 {
   		 config|=SPI_CON_MSTEN;
   	 }
   	 if(frmEn)
   	 {
   		 config|=SPI_CON_FRMEN;
   		 if(!frmMaster) {   
   			 config|=SPI_CON_FRMSYNC;
      	 }
   	 }
  	 SpiChnOpen(chn, config, 4);	// divide fpb by 4, configure the I/O ports. Not using SS in this example
 }
 
 // ******************************************************
 /*      
 	Function:	spi_send_read_byte
 	Inputs:		unsigned char byte
   	Outputs:	unsigned short rxData
     
	This function is required by the 24L01 header file. 
   	It takes the inputted byte, sends it over the chosen 
   	SPI channel, then waits to retreive data back. 
 */      
 // ****************************************************** 
 unsigned char spi_send_read_byte(unsigned char byte) {
  	 unsigned short	txData, rxData; // transmit, receive characters
   	 int chn = 1; // SPI channel to use (1 or 2)
  	 
   	 txData = byte; // take inputted byte and store into txData   
   	 SpiChnPutC(chn, txData);			// send data
 	 rxData = SpiChnGetC(chn);			// retreive over channel chn the received data into rxData
    
  	 return rxData; 
 }
 
 
  // ******************************************************
  /*
   
  	 Functions:	Delayms, Delayus
  	 Inputs:	unsigned t
  	 Outputs:	none
   
  	 These functions are required by the 24L01 header file. 
   	 They take an input of t (ms, us) and delay the 
  	 program. 
   
  */
  // ****************************************************** 
 void Delayms( unsigned t) {
  	// This uses Timer 1, can be changed to another timer. Assumes FPB = SYS_FREQ
  	OpenTimer1(T1_ON | T1_PS_1_256, 0xFFFF);
  	while (t--)
  	{  // t x 1ms loop
  		WriteTimer1(0);
  		while (ReadTimer1() < SYS_FREQ/256/1000);
  	}
  	CloseTimer1();
 } // Delayms
 
 void Delayus( unsigned t) {
  	OpenTimer1(T1_ON | T1_PS_1_256, 0xFFFF);
  	while (t--)
  	{  // t x 1ms loop
  		WriteTimer1(0);
  		while (ReadTimer1() < SYS_FREQ/256/1000000);
  	}
  	CloseTimer1();
 } // Delayus

Receiver Code

// ************************************************************** 
/*

	WirelessReceiver.c
	Lab 5: High-speed Wireless Communication
	Jonathan Drake, Caitlin Ramsey 
	2010-02-16
	
	This code initializes the nRF24L01+ chip as a receiver to 
	continuously listen over its wireless antenna. If data is 
	received, the program prints the data on a PC. The loop contains
	code to both output the program's status to the PC via RS232
	cable and onboard LEDs. 

*/ 
// **************************************************************
 

// Includes
#include "HardwareProfile.h"
#include "nrf24l01.h"


// Function Declarations
// Note: Descriptions of functions found after main() function
void Initialize(void);
void InitializeIO(void);
void SpiInitDevice(int chn, int isMaster, int frmEn, int frmMaster);
void initUART2(int pbClk);
unsigned char spi_send_read_byte(unsigned char byte);
void Delayms( unsigned t);
void Delayus( unsigned t);
void Delaytus( unsigned t);


// Constants
#define DESIRED_BAUDRATE (19200) // The desired BaudRate for RS232 communication w/ UART

// Main Function
int main(void)
{
	// initialize onboard LEDs, IO pins, UART2, SPI1, set up nRF24L01+ as RX
	Initialize(); 

	char RS232_Out_Buffer[64]; // buffer for printing data to the screen via UART
	unsigned char data; //register to hold letter sent and received
	
	while(1)
	{
		nrf24l01_irq_clear_all(); //clear all interrupts in the 24L01
		nrf24l01_set_as_rx(true); // force 24L01 to be a receiver (this is a double-check)

		// is the 24L01 activated?
		if (nrf24l01_irq_pin_active()) {
			mLED_1_On();
		} else {
			mLED_1_Off();
		}

		// is the 24L01 receiving data?
		if (nrf24l01_irq_rx_dr_active()) {
			mLED_2_On();
		} else {
			mLED_2_Off();
		}		

		//check to see if the data has been received.  if so, get the data
		if((nrf24l01_irq_pin_active() && nrf24l01_irq_rx_dr_active()))
		{
			mLED_3_On();
			nrf24l01_read_rx_payload(&data, 1); //get the payload into data
			sprintf(RS232_Out_Buffer, "\r\nrec data = %d\r\n", data); // show the data
			putsUART2(RS232_Out_Buffer);
			Delayms(2000);
		} else { // otherwise, show that chip is still listening
			putsUART2("...\r");
		}

		// toggle onboard LED 3 to indicate loop iterating
		mLED_3_Off();
		Delayms(10);
	}

}

// Initialize all initialize functions (function descriptions to follow)
void Initialize(void) {

	// initialize peripheral bus clock to SYS_FREQ (80 MHz)    
	int	pbClk;
	pbClk = SYSTEMConfigPerformance(SYS_FREQ);
	
	// initialize UART   
	initUART2(pbClk);	
	
	// initialize input/output pins     
	InitializeIO();
	
	// initialize the SPI channel 1 as master, no frame mode   
	SpiInitDevice(1, 1, 0, 0);	   
	
	//initialize 24L01 to debug configuration as receiver, 1 byte data size, and auto-acknowledge mode disabled   
	nrf24l01_initialize_debug(true, 1, false);   
	
	// initialize all onboard LEDs on NU32   
	mInitAllLEDs();    
	
	// if program initialized correctly, indicate on PC & onboard LEDs     
	putsUART2("\r\n***** System Initialized *****\r\n");    
	mLED_0_On();   

}

// initialize IO pins
void InitializeIO(void) {	
	TRISBbits.TRISB0 = 1; // set IRQ pin as input
	TRISC = 0xFFF9; // make CSN, CE digital outputs
	PORTC = 0x0004; // set CSN bit active
}

// initialize UART2
void initUART2(int pbClk)
{
	#define config1 	UART_EN | UART_IDLE_CON | UART_RX_TX | UART_DIS_WAKE | UART_DIS_LOOPBACK | UART_DIS_ABAUD | UART_NO_PAR_8BIT | UART_1STOPBIT | UART_IRDA_DIS | UART_DIS_BCLK_CTS_RTS| UART_NORMAL_RX | UART_BRGH_SIXTEEN
	#define config2		UART_TX_PIN_LOW | UART_RX_ENABLE | UART_TX_ENABLE | UART_INT_TX | UART_INT_RX_CHAR | UART_ADR_DETECT_DIS | UART_RX_OVERRUN_CLEAR	
 	OpenUART2( config1, config2, pbClk/16/DESIRED_BAUDRATE-1);	// calculate actual BAUD generate value.
 	ConfigIntUART2(UART_INT_PR2 | UART_RX_INT_EN);
}


// initialize SPI
void SpiInitDevice(int chn, int isMaster, int frmEn, int frmMaster)
{
	unsigned int config = SPI_CON_MODE16|SPI_CON_SMP|SPI_CON_ON;	// SPI configuration word
	if(isMaster)
	{
		config|=SPI_CON_MSTEN;
	}
	if(frmEn)
	{
		config|=SPI_CON_FRMEN;
		if(!frmMaster)
		{
			config|=SPI_CON_FRMSYNC;
		}
	}
	SpiChnOpen(chn, config, 4);	// divide fpb by 4, configure the I/O ports. Not using SS in this example
}

// ******************************************************
/*      
	Function:	spi_send_read_byte
	Inputs:		unsigned char byte
  	Outputs:	unsigned short rxData
    
	This function is required by the 24L01 header file. 
  	It takes the inputted byte, sends it over the chosen 
  	SPI channel, then waits to retreive data back. 
*/      
// ****************************************************** 
unsigned char spi_send_read_byte(unsigned char byte) {
 	 unsigned short	txData, rxData; // transmit, receive characters
  	 int chn = 1; // SPI channel to use (1 or 2)
 	 
  	 txData = byte; // take inputted byte and store into txData   
  	 SpiChnPutC(chn, txData);			// send data
	 rxData = SpiChnGetC(chn);			// retreive over channel chn the received data into rxData
   
 	 return rxData; 
}


// ******************************************************
/*
 
	 Functions:	Delayms, Delayus
	 Inputs:	unsigned t
	 Outputs:	none
 
	 These functions are required by the 24L01 header file. 
 	 They take an input of t (ms, us) and delay the 
	 program. 
 
*/
// ****************************************************** 
void Delayms( unsigned t) {
 	// This uses Timer 1, can be changed to another timer. Assumes FPB = SYS_FREQ
 	OpenTimer1(T1_ON | T1_PS_1_256, 0xFFFF);
 	while (t--)
 	{  // t x 1ms loop
 		WriteTimer1(0);
 		while (ReadTimer1() < SYS_FREQ/256/1000);
 	}
 	CloseTimer1();
} // Delayms

void Delayus( unsigned t) {
 	OpenTimer1(T1_ON | T1_PS_1_256, 0xFFFF);
 	while (t--)
 	{  // t x 1ms loop
 		WriteTimer1(0);
 		while (ReadTimer1() < SYS_FREQ/256/1000000);
 	}
 	CloseTimer1();
} // Delayus