For all the C guys out there. Need pointer advice.

What is the address of the variable Uint32 Flash?  I would find it very coincidental that the variable Flash resides at address 0x3F7FF, but please check this.

The reason I ask is that I interpret the following statement you have :

FlashAddr = &Flash ;

as assigning the address of the variable Flash to the contents of FlashAddr rather than the value pointed to by contents of the variable Flash.

I would have used :

FlashAddr = 0x3F7FFFF ;

Exactly what I discovered.  I know I'm doing the pointer wrong and *FlashAddr = 0x3F7FFF when I want FlashAddr = 0x3F7FFF.  However, when I try to put in FlashAddr = 0x3F7FFF, I get a complaint from the compiler that I can't load a long into a pointer.

When I make FlashAddr an int32 (rather than a pointer), make FlashAddr = 03F7FFF, and fix the function calls the compiler complains that that "operand of * must be a pointer" on this line of the function:

crc ^= *buf++ << 8;

If I don't fix the function calls (leave them as pointers) the compiler complains that "Uint32 is incompatible with Uint32 *" referring to the calling function:

CRC = crc16(FlashAddr, 0x3FFF);

You could cast FlashAddr during the function call, as in :

CRC = crc16((Uint32 *)FlashAddr, 0x3FFF) ;

I think I've got it but I'm not sure.  At least I no longer have a random number generator.  Here is what I have now: 

unsigned short crc16(Uint32*, Uint16);

// Global variables 

unsigned short CRC;
Uint32 Flash = 0x3F7FFF;
Uint32 *FlashAddr;


main()
{
FlashAddr = &Flash;
CRC = crc16(FlashAddr, 0x3FFD);
Fail(); // Just so I stop after the calculation.
}


unsigned short crc16(Uint32 *buf, Uint16 len )
{
	unsigned short crc = 0;
	while( len-- ) {
		int i;
		BitData.MOT_SPD = *(Uint16 *)buf;
		crc ^= *(Uint16 *)buf++ << 8;
		for( i = 0; i < 8; ++i ) {
			if( crc & 0x8000 )
				crc = (crc << 1) ^ 0x1021;
			else
				crc = crc << 1;
		}
	}
	return crc;
}

I realize it's a little convoluted but I got the same results when I used the casting.  I'll clean it up and cast it later as soon as I solve the last problem.  I get the same CRC each time unless I recompile.  Then I get a new CRC that stays the same each time until I recompile again.  Is there something that happens in flash (so far I'm still running out of ram) that might change it?

P.S. I'm having trouble copying and pasting code into E2E.

I think you should just cast the constant when you assign it like this

Uinit32* flash_addr = (Uint32*)0x3F7FFF;

Then the type checking should all work out.

Jim Noxon

There is nothing inherent in flash that should change from compile to compile, unless something in your application is actually allocated to a region of memory in flash.  Although you have not stated this specifically, I assume you are using a C2000 device.

Take a look at the map file that can be generated from the code generation tools.  This will indicate where variables, functions, etc. are linked to and will give you an idea if something is being allocated to flash which might change from compile to compile.

Thanks Norman,

I spent a lot of time going back and forth on the code and by the time I posted my message, my ending address had become my starting address.  I figured this out Friday (hey, I'm a hardware engineer).  I also figured out that the code wasn't incrementing the address (it does now).  My last item to fix will be why my data is 0x4000 when I should be seeing 0xFFFF in the memory.  I'll work on this today.

The original code for CRC was pulled off the internet because I had never used CRC before.  The processor I'm using is the SM320F2808.