Referencing C variables in In-line assembly

zevious · Feb 5, 2009

Hi,

I'm wrote a small 18F in-line assembly snippet in MPLAB referencing a local C variable. From the results I'm not referencing the C variable correctly.

Any ideas?

unsigned char count = 0;
unsigned char current_count = 10;

count = current_count;

_asm

// Loop until count is 0
start:
DECFSZ count, 1, 0
BRA start
GOTO done
done:

_endasm

Pommie · Feb 6, 2009

To use a variable without managing the banking you need to have it in access ram. Try moving your variable so it is global and put it in the access area by doing,

Code:

#pragma udata access somename
near unsigned char count;
#pragma udata

Mike.

zevious · Feb 6, 2009

Thanks Mike,

How would I manage the banking to avoid allocating it in access ram?

Pommie · Feb 6, 2009

Well, if you run out of access ram you need to load the bsr with the bank number of your variable. What is wrong with using the access ram, the compiler doesn't seem to!!

Mike.

zevious · Feb 6, 2009

Thanks again Mike,

I believe I can use access RAM (near), and it do sound like it would end up being faster and require less cycles. But lets say I wanted to set the BSR with bank information to access the count variable in my simple loop example above. How would I accomplish that?

I am sorry for these newbie questions but I'm just starting up with MPASM syntax (as you can tell)

Pommie · Feb 6, 2009

You would simply do movlb count.

Mike.

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Referencing C variables in In-line assembly

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