>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 13 June 2005 11:01
>To: piclist@mit.edu
>Subject: [PIC] Error messages when inserting Assembler code into C
>
>
>I am trying to insert some assembler code into my C code.  The 
>micro I use is a PIC18F8720 with the HI-TECH compiler. I am 
>using a global variable that is accessed in C and assembler 
>and unless I use near RAM I can not get most assembler 
>instructions to work.
>
>char varib;
>void func(void)
>{
>#asm
>
>	movff	wreg,_varib		//works fine
>	addwf	_varib		//does not compile is this line is added
>
>#endasm
>}
>
>When I compile I get this message:
>Fixup overflow referencing psect bigbss (loc 0x19E28 
>(0x19DD6+82), size 1, value 0xB67)
>
>The varib variable is stored at 0xB67 so I thought it may be a 
>banking problem. If anyone can be of help it will be greatly 
>appreciated.

Once you start adding inline assembler into your C code you lose the advantages that the compiler gives you such as portability and in the PIC's case automatic handling of data memory banking.  If you really need to do this, you will have to manipulate the bank select register yourself.  The reason that the first instruction works ok is that movff takes a 12bit address for it's operands so no banking instructions are required.  The code below should compile ok:

char varib;
void func(void)
{
#asm

	movff	wreg,_varib		; no bank switching required

	movlb	_varib shr 8	; set bank using high order bits of _varib address
	addwf	_varib & 0xFF	; use lower 8 bits of _varib address in operand

#endasm
}

Regards

Mike

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