dsPIC EEPROM read/write

This code provides a simple example of reading and writing to EEPROM on a dsPIC30F4011 using a couple of functions adapted from http://www.microchip.com/forums/fb.ashx?m=417425.

/*
* David Dorran           03/05/13 Adapted from http://www.microchip.com/forums/fb.ashx?m=417425 to use offsets rather than explicit address locations. 
* Additional Notes: Tested on dspic30f4011
**********************************************************************/

#include <p30f4011.h>
#include <libpic30.h>
#include <stdio.h>
#define ERASE_WORD 0x4044
#define WRITE_WORD 0x4004
#define ADDRESS_HI 0x007F
#define EEPROM_LOW_START_ADDRESS 0xFC00
#define TRUE 1

// Configuration settings
_FOSC(CSW_FSCM_OFF & FRC_PLL16); // Fosc=16x7.5MHz, Fcy=30MHz
_FWDT(WDT_OFF);                  // Watchdog timer off
_FBORPOR(MCLR_DIS);              // Disable reset pin

void Eeprom_WriteWord(unsigned short  pushAddressOffset, unsigned short value);
unsigned short Eeprom_ReadWord(unsigned short  pushAddressOffset);

int main(void)
{
	unsigned short value;
    // Setup UART for debugging
    U1BRG = 48;            // 38400 baud @ 30 MIPS
    U1MODEbits.UARTEN = 1; // Enable UART
	
	Eeprom_WriteWord(8, 0x2345 ); //write the wordlength value 0x2345 to the 8th available EEPROM memory location
	Eeprom_WriteWord(13, 0x4612 );
	Eeprom_WriteWord(84, 0xf123 );
	
	value = Eeprom_ReadWord(13); //Read the vword stored in the 13th available EEPROM memory location (should be 0x4612)
	printf("\nRead value = %x\n", value);
    while(1);
}

unsigned short Eeprom_ReadWord(unsigned short  pushAddressOffset) {
   unsigned short ushResult;
   register int eedata_addr; 
   register int eedata_val; 
  unsigned short pushAddress;
   pushAddressOffset = pushAddressOffset*2; //word offset , byte addressable so multiply by 2
   pushAddress = pushAddressOffset + EEPROM_LOW_START_ADDRESS;
   
   TBLPAG = ADDRESS_HI; // __builtin_tblpage()
   eedata_addr = (unsigned short)pushAddress; // __builtin_tbloffset()
   __asm__("TBLRDL [%[addr]], %[val]" : [val]"=r"(eedata_val) : [addr]"r"(eedata_addr)); 
  
   ushResult = eedata_val; 
   return (ushResult);
 }

void Eeprom_WriteWord(unsigned short  pushAddressOffset, unsigned short value) {
  unsigned short pushAddress;
   pushAddressOffset = pushAddressOffset*2; //word offset , byte addressable so multiply by 2
   pushAddress = pushAddressOffset + EEPROM_LOW_START_ADDRESS;
   TBLPAG = ADDRESS_HI;
   NVMADRU = ADDRESS_HI; // Write address of word to be erased into NVMADRU, NVMADR registers.
   NVMADR = (unsigned short) pushAddress;

   NVMCON = ERASE_WORD; // Setup NVMCON register to erase one EEPROM word.
   
   //PROTECT_CODE_FROM_INTERRUPTS_START // Disable interrupts while the KEY sequence is written
      NVMKEY = 0x55; // Write the KEY sequence step1
      NVMKEY = 0xAA; // step2
      NVMCONbits.WR = TRUE; // Start the erase cycle
   //PROTECT_CODE_FROM_INTERRUPTS_STOP // Enable interrupts
   
   while (NVMCONbits.WR == TRUE); // wait for the EEPROMS
   
   NVMCON = WRITE_WORD; // Setup NVMCON register to write one EEPROM word. 
   {
      register int eedata_addr; 
      register int eedata_val; 
      
      eedata_addr = (unsigned short)pushAddress; // write low word of address
      eedata_val = value; // write data
      
      __asm__ volatile ("TBLWTL %[val], [%[addr]]" : [val]"+r"(eedata_val) : [addr]"r"(eedata_addr));
   }
   
	NVMCON = WRITE_WORD;
   //PROTECT_CODE_FROM_INTERRUPTS_START // Disable interrupts while the KEY sequence is written
      NVMKEY = 0x55; // Write the KEY sequence step1
      NVMKEY = 0xAA; // step2
      NVMCONbits.WR = TRUE; // Start the erase cycle
   //PROTECT_CODE_FROM_INTERRUPTS_STOP // Enable interrupts
   
   while (NVMCONbits.WR == TRUE); // wait for the word to be written
   
   // no proper watchdog protection in the 2 while loops
   // no proper check if bytes are written correctly by re-reading them
 }
 

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