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What does this code mean?

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Christophe

Joined: 10 May 2005
Posts: 323
Location: Belgium

What does this code mean?

Posted: Tue Apr 07, 2009 9:14 am

Hi,

this piece of code is at the end of my bootloader. It should reset the PIC but it doesn't. Can you help me understand what these commands mean? I ported the code from PIC16LF877A to PIC16F886:

Code:

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

asmallri

Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia

Re: What does this code mean?

Posted: Tue Apr 07, 2009 9:37 am

Christophe wrote:

Hi,

this piece of code is at the end of my bootloader. It should reset the PIC but it doesn't. Can you help me understand what these commands mean? I ported the code from PIC16LF877A to PIC16F886:

Code:

Well it will not help you because as the comment says, this code is overwritten by the user reset vector information extracted from the target applications hex file.

Never the less... The PIC16F does not have a reset instruction so to emulate a reset you need to setup the high program counter byte latch (PCLATH) at 0x0A to point to low memory. After you set PCLATH the next call or goto instruction executed will load this value into the high order of the program counter so goto 0x00 is really goto PCLATH | 0x00
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

Christophe

Joined: 10 May 2005
Posts: 323
Location: Belgium

Posted: Tue Apr 07, 2009 9:42 am

I don't understand why my application does not reset after writing to the program memory. Only after pressing the MCLR (reset), the bootvector from the program HEX file is loaded or the program is launched.

Here's the code:

Code:

#include <16F886.H>
#device *=16
//#case
#fuses XT, PUT, NOWDT, NOPROTECT, NOLVP, NOCPD, NOWRT, BROWNOUT
#define READY_FOR_NEXT 0x11 // define possible reply bytes
#define FINISH_FLAG 0x55
#define BOOTLOADER_OVERWRITE 0x80
#define SerBufferSize 45 // serial input buffer size

#include "GOGOLOADER.H"
#ORG LOADER_BEGIN, LOADER_END auto=0 default // #org tells the compiler where to put the procedures in memory
#use DELAY (clock=4000000)
#use rs232 (baud = 19200, parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8)

unsigned int a2i (unsigned char asciiByte) // a slim version of atoi().converts ascii text to integer
{ // i.e. '1' = 1, 'A' = 10
if (asciiByte >= 'A' && asciiByte <= 'F')
return((asciiByte) - 'A' + 10);
else if (asciiByte >= '0' && asciiByte <= '9')
return ( asciiByte - '0');
}

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

void main ()
{
unsigned int16 Buffer[SerBufferSize]; // serial input buffer
int1 notDone = 1, CODE_TOO_LARGE = FALSE;
unsigned int recLen; // HEX file record length
unsigned int16 writeAddr, timeout = 0; // HEX file write address
unsigned char recType; // HEX file record type
unsigned char i=0,j, triggers_found = 0; // general counters
unsigned int16 UserBootVectorAddr; // holds the address of our new boot vector
unsigned int16 User_BootVector [4] = { 0,0,0,0 };

for ( i = 2; i > 0 ; i-- )
{
while ( !kbhit () && (++timeout < 0xFFFF) ) // 2 Seconden tijd om downloadcommando te sturen: 0xAA , 0xAA
delay_us (16);

if ( kbhit () )
{
if ( getc () == 170 )
triggers_found++;
else
break;
}
}

if ( triggers_found == 2 )
{
putc ('L');
UserBootVectorAddr=label_address(UserBootVector); // Get the adress in the bootloader where the reset vector will be
while (notDone)
{
while (getc() != ':') ; // Wait for ':'
recLen = read8(); // Hex file Record length
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).
writeAddr = ((int16)read8() << 8) + read8(); // Write Address
writeAddr >>= 1; // divide by 2
// The physical address on the PIC is half the address in the HEX file.
getc (); // ignore the first digit, it is always '0'
recType = getc(); // Get the Rec Type

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 ((writeAddr >= 0x2100) && (writeAddr <= 0x21FF)) // if data is in the EEPROM area
write_eeprom((int) writeAddr, (int) Buffer[i]);

else if ((writeAddr >= 0x2000) && (writeAddr <= 0x20FF)) // else if data is in the Configuration register area
{} // Can't write configuration registers -> just skip.

else if ( (writeAddr >= LOADER_BEGIN) && (writeAddr <= LOADER_END)) // else if data overlaps the bootloader code -> halt
{
CODE_TOO_LARGE = TRUE;
break;
}
else
{ // else -> data is in program area
for (i=0; i < recLen ;i++)
{
if (!CODE_TOO_LARGE)
{
if ((writeAddr < 0x004) && (i<4) )
{
User_BootVector[i] = Buffer[i];
}
else
write_program_eeprom (writeAddr + i, Buffer[i]);
}
}
}
putc (READY_FOR_NEXT); // Tells the PC to send the next line
}
}
if ( CODE_TOO_LARGE )
putc ( BOOTLOADER_OVERWRITE );
else
{
for ( i=0; i < 4 ;i++)
write_program_eeprom (UserBootVectorAddr + i, User_BootVector[i] );
putc ( FINISH_FLAG ); // Tells the PC that we are finished
}
for (j=0;j<255;j++) // this loop gives the chip time to finish sending the serial byte before resetting it self.
{
for (i=0;i<255;i++) {};
}
//delay_ms ( 2 );
} // While notdone

UserBootVector:
#asm // This is a reboot command written in Assembly.
MOVLW 0x00 // these four commands will be overwritten with the boot vector we obtain from the HEX file.
MOVWF 0x0A
GOTO 0x00
NOP
NOP
#endasm
}// main
#ORG default

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