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Hi all

I'm developing an application in C18 on the 18F6520.

I have an ISR that looks for characters on serial port1 

It uses the getcUSART1 function to retrieve each character.

Depending on the character it shoves a cmd on a circular buffer unless it is
a special character then it builds a string till a terminating character
arrives or if it is neither a command character or a special character I
just drop it and wait for the next one to arrive.

The circular buffer is about a hundred characters long and will over write
old commands if the buffer is not emptied in time by my main loop.so this
should not cause problems (other than dropping commands of
course)....provided I don't have a stupid coding mistake.

The building of a string is either done when it is eight characters long or
it is dropped too.

 

All is well till I send charters without letting up (I just hold down a key
on a terminal emulator) for an extended periods of time.

Then strange things seem to happen sometimes the ultoa function starts
returning nonsense strings.  

I don't think it has anything to do with ultoa other than it needs stack
space to do its thing.

 

My reasoning goes like this as I call getcUSART1 again and again if I don't
allow the last getcUSART1 to finish before my next ISR happens eventually
I'll over flow the stack and strange things will start to happen.

Now I want  increase my clock speed and stack size till I can keep up but
there might always be point where external events happen faster than I am
able to respond no matter how fast I run my device.

So I need to know a couple of things.

 

One how do I increase my stack size (I'm using the linker script file ).

And two in order to keep from pushing this problem down the road and having
the same issue even when I'm running faster how do I tell in my ISR if I'm
about to run out of resources so I can start dropping characters instead
continuing to calling getcUSART1and overflowing the stack?

(assuming this is what is happening )

This way I can fail gracefully and maybe send a message to the
user/interface to knock it off till I am not so over whelmed instead of
running out of stack size and crashing or sending nonsense to the
user/interface.

 

Phillip

Things should be as simple as possible but no simpler

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Phillip Coiner

CTO, GPS Source, Inc.

 

 

Your source for quality GNSS Networking Solutions and Design Services, Now!

 


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