goto_address and label_address problems!

Guest · Guest

I'm having problems when using the goto_address and label_address functions. They seem to work perfectly when used within the same function as the label is located, but as soon as I move the label outside the function that calls the goto_address(label_address(....)) bit of my code, the compiler complains with error 88: Undefined label that was used in a GOTO > start2

My code looks like this:

start2:
function1(void)
{
.....
.....
}

function2(void)
{
....
goto_address(label_address(start2));
....
}

Thanks for any help on why this appears/how to fix it!

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

You can't put a label outside of a function.

Tell us what your overall purpose is.

Guest · Guest

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Normally this would be done from main(). You would have a while(1)
loop in main() that periodically checks an interrupt-driven RS-232 receive
buffer to see if there is a char available. If there is a char available,
then fetch it, and check it to see if it's your "reset" command char.
If so, then call your init function.

Guest · Guest

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

You shouldn't have to check for the incoming character at several
places in the program. There should be just one central routine
that checks incoming characters and calls the appropriate function
based on the received command. If you want to do something
else, maybe someone else can respond.

Guest · Guest

OK thanks for your help PCM Programmer. Perhaps I didn't explain myself quite right.

Anyways, I had a closer look at the documentation and found in the explanation for label_address() it says:

"Parameters: label is a C label anywhere in the function"

So aparantly it cannot handle labels outside the function, but the goto_address() function can. I find that a bit odd to have 2 functions that complement each other not working as you would expect.

I think I will just make a workaround and fix the initilisation routine in ROM at a known address and use the goto_address() function to goto that known ROM address.

Thanks.

Ttelmah · Guest

In the 'long term', what your are trying to do, would cause problems. There is nothing to tidy up the stack. When you are inside 'function2', the return address on the stack, is the point at which this function was called. If you jump into 'function1', then when it finishes, it will return you to the function2 return address...
This is why jumps 'trans function', are potentially lethal traps.

You can 'cross jump', by coding like this:

Guest · Guest

Thanks Ttelmah. You have solved my problem!
I never thought about declaring the address as a global variable. Very annoying because its such a simple fix. I would buy you a beer if I could!

I don't believe I will have any stack issues in my case, because where I will be jumping to is inside main() (where I will then call my initialisation function) and becuase main() never returns then it shouldn't be a problem. The values on the stack before will just stay there and possibly drop off the end when the stack fills up (if my knowledge is correct).

Thanks again!

Ttelmah · Guest

OK. A target inside main, should be alright in this regard.
You should make sure you disable the stack full 'reset' option on your chip (if it has this), otherwise you may get a problem (NOSTVREN in the fuses).

Happy New Year to everybody

Best Wishes