Random CONST CHAR

Markdem · Joined: 24 Jun 2005 Posts: 206

I have got a problem I can't work out..
CCS = 5.025

I have the following:

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Ttelmah · Joined: 11 Mar 2010 Posts: 19506

Some comments:

You say in your post header 'random const char', but this is not a 'const'.
What happens is that:

"Content-Length:"

is a const, but declared as 'static', this is copied into the RAM string
http_len_str, _once_ before the main code actually runs. Never again.
So if anything else at all talks to the RAM area containing this string, any
changes will be retained.
Now when you remove 'static', this value is instead copied into the
http_len_str, every time the routine starts.
So I'd suspect that something is accidentally changing the 15th byte
of http_len_str. Result you see this changed byte when you stop and
look at the variable in the debugger.
Given that the 'non static' version is OK, look later in the routine(s) than
where you are stopping and looking at the value.
As PCM says, 5.025, is a rather old version, but I'd be most suspicious
that you actually have a code error resulting in the byte being changed.

Markdem · Joined: 24 Jun 2005 Posts: 206

Sorry for the late reply,..

I tried the demo, still have the same issue.

Ttelmah - what you are saying makes sense, however I have no idea how I would ever debug this. Is there away of checking what memory location is given to "http_len_str[]" and using the debugger to watch for change? I know I can do this in visual studio but no idea how I would do it using MPLab\CCS.

And does it really matter anyway? I am guessing it takes a few extra ns to run the function but besides that, what else should I be thinking about?

Thanks

Ttelmah · Joined: 11 Mar 2010 Posts: 19506

The ways to debug are first, to look at the .sym file.
Find where this variable is, and look what is immediately in front of this
in memory. The most likely culprit is always another variable 'nearby'.
Just after as well, but slightly less likely.
Then look in your code for every operation that does anything involving the
nearby variables. Particularly anything involving pointers (array operations,
string operations etc..).
When you are running the debugger, the 'watch' values do not update, till
you stop. So you have to split the code up, and run a small section, and
see if the watch has changed. You can do a sort of 'binary search', with
a pair of breakpoints gradually being moved closer and closer together, till
you isolate where the change occurs.