bootloader877a10.c

PIC Boot Loader for the 16F877A MCU.

/////////////////////////////////////////////////////////////////////////////
//
//       =================================================
//
//       This code is released under the GPL license. Read the attached license
//       for full information but here's the basic points:
//        - Use it freely
//        - Let others use your new/modified code freely too
//        - So, please release the source
//
//       =================================================
//
//       PIC Boot Loader for the 16F877A MCU
//       V. 1.0 Nov 22, 2006
//       By Arnan (Roger) Sipitakiat
//       http://www.gogoboard.org
//
//       This code is designed for the GoGo board
//       but it should work with any 877A PIC device.
//
//       The loader will start when pin B7 is set high during
//       power-up.
//
//       The loader occupies memory addresses between 0x1e50-0x1fff (0.4k)
//       User code must not use this memory segment.
//       in CCS, you can use the following command to reserve the memory space
//          #ORG 0x1e50, 0x1fff {}
//
//       Note that the configuration bits can't be changed. Whatever is used
//       here is what the user's program is stuck with.
//
/////////////////////////////////////////////////////////////////////////////


#include <16F877A.H>
#device ADC=10 *=16

#case

#fuses HS,NOWDT,NOPROTECT, BROWNOUT, NOLVP, PUT

#use DELAY(clock=20000000)

#use rs232(baud=19200, xmit=PIN_C6, rcv=PIN_C7)

// define possible reply bytes
#define READY_FOR_NEXT  0x11
#define FINISH_FLAG     0x55
#define BOOTLOADER_OVERWRITE  0x80

#define LOADER_BEGIN      0x1E50
#define LOADER_END        0x1FFF

#define SerBufferSize 45  // serial input buffer size

#define RUN_BUTTON   PIN_B7
#define RUN_LED      PIN_B6
#define USER_LED     PIN_D0

// #org tells the compiler where to put the procedures in memory
#ORG LOADER_BEGIN, LOADER_END auto=0 default

// a slim version of atoi().
// converts ascii text to integer
// i.e. '1' = 1, 'A' = 10
unsigned int a2i(unsigned char asciiByte) {

      if (asciiByte >= 'A' && asciiByte <= 'F')
         return((asciiByte) - 'A' + 10);
      else if (asciiByte >= '0' && asciiByte <= '9')
         return( asciiByte - '0');
}


// convert two ascii text to a 8 bit integer
unsigned int read8() {
     return( (a2i(getc()) << 4) + (a2i(getc())) );
}


void main()
{
   unsigned int16 Buffer[SerBufferSize];  // serial input buffer
   int1 notDone = 1;

   unsigned int recLen;   // HEX file record length
   unsigned int16 writeAddr;  // HEX file write address
   unsigned char recType;  // HEX file record type

   unsigned char i=0,j;   // general counters
   unsigned int16 UserBootVectorAddr; // holds the address of our new boot vector

   if (input(RUN_BUTTON) ) {

      UserBootVectorAddr=label_address(UserBootVector);

      output_high(RUN_LED); output_high(USER_LED);

      while (notDone) {

         //////////////////////////////////////////
         /// Wait for ':'

         while (getc() != ':') ;

         /////////////////////////////////////////
         //  Record length

         recLen = read8();
         recLen >>= 1;  // we divided the Length by 2.
                        // Each memory location on the PIC (16 bit) is
                        // twice the unit size of the HEX file (8 bit).

         /////////////////////////////////////////
         //  Write Address

         writeAddr  = ((int16)read8() << 8) + read8();

         writeAddr >>= 1;  // divide by 2
                        // The physical address on the PIC is half the
                        // address in the HEX file.

         /////////////////////////////////////////
         //  Rec Type

         getc();  // ignore the first digit, it is always '0'
         recType = getc();

         if (recType == '1') { // End of file record
            notDone = 0;

         } else if (recType == '0') { // data record

            /// get the data
            for (i=0; i < recLen ; i++) {
                Buffer[i] = read8() + ((int16)read8() << 8);
            }

            // if data is in the EEPROM area
            if ((writeAddr >= 0x2100) && (writeAddr <= 0x21FF)) {
               write_eeprom((int) writeAddr, (int) Buffer[i]);
            }
            // else if data is in the Configuration register area
            else if ((writeAddr >= 0x2000) && (writeAddr <= 0x20FF)) {
               // Can't write configuration registers -> just skip.
            }

            // else if data overlaps the bootloader code -> halt
            else if ((writeAddr >= LOADER_BEGIN) && (writeAddr <= LOADER_END)) {

               putc(BOOTLOADER_OVERWRITE);
/*               while (1) {
                  output_high(RUN_LED);
                  delay_ms(300);
                  output_low(RUN_LED);
                  delay_ms(300);
               }
*/            }

            // else -> data is in program area
            else {
               for (i=0; i<recLen ;i++) {
                  // (*) Modifing the Boot Vector

                  // The first four commands in memory are called the boot
                  // vector. It resets the board and points to the address of
                  // the main function.

                  // Each HEX file has their own version of these commands. But
                  // since we always want the boot loader to run before the
                  // user code, we must not overwrite the loader's boot vertor.
                  // Instead, we move the user's boot vector to another location
                  // within the boot loader's program area
                  // (see label "UserBootVector" below).

                  // This 'if' command detects user's boot vector and redirects it
                  // The boot vector is at address 0x0000 - 0x0003
                  if ((writeAddr < 0x004) && (i<4) )
                     write_program_eeprom(UserBootVectorAddr + i, Buffer[i]);
                  else
                     write_program_eeprom(writeAddr + i, Buffer[i]);
               }

            }
            // Tells the PC to send the next line
            putc(READY_FOR_NEXT);


         }


      }

      // Tells the PC that we are finished
      putc(FINISH_FLAG);
      for (j=0;j<255;j++) {
         for (i=0;i<255;i++) {}; // this loop gives the chip time to finish
                                 // sending the serial byte before resetting it self.
                                 // I did not use delay_ms() because I have had
                                 // some strange problems with it.
      }

   }

// This is a reboot command written in Assembly.
// these four commands will be overwritten with the boot vector we obtain
// from the HEX file.
// See (*) above for more info.
UserBootVector:
      #asm
      MOVLW   0x00
      MOVWF   0x0A
      GOTO   0x00
      NOP
      NOP
      #endasm

}


#ORG default