AVR-Chat

I'm fairly sure that I'm into a stack overflow/buffer overrun bug in my (FreeRTOS
based) application on an ATMega32A.

It gets through initialization and initial task creation but very shortly after that
it re-executes the "main" function (as shown by a breakpoint).  My guess is that
this is most likely due to executing a 'return' through a clobbered stack
frame/marker.

I think I need to understand WinAVR frames better to track this down - besides, I
should know it anyway ...

Can someone suggest a good web site/doc where I can read about the stack
frames/markers produced by WinAVR (GCC)?

At the moment, I'm trying to 'sneak up on it' with breakpoints, UART traces,
disabling sections of code, disabling interrupt handlers, etc.  FreeRTOS has some
stack overflow detection logic (which I have turned on) but, AFAIK, it is only
invoked on task switches.

Another question:  Is there a way to have WinAVR emit a macro/function invocation on
function entry and exit?  This would help 'instrument' the code with verification
logic.  I know I can insert my own but I wondered if there was a WinAVR supported
way to do this quickly and thoroughly.

A "stack trace back" would be nice but it's not available in AVRStudio.  I have not
yet gotten up the GDB (which I believe does have a stack trace back) interface in
the Code::Blocks IDE yet (maybe my time would be well spent on that ...).

Other than that, and suggestions on tracking this down would be welcome.

General Pondering:  Stack overflow can be a difficult problem because, particularly
in embedded systems, it is dependent on the 'worst case' stack depth which is
subject to interrupt timing, etc.  I wonder why processor manufacturers have not
added a hardware "Stack Fence", such that, if the stack grows past this a trap
occurs.  Sure would be nice for me at the moment and, I suspect, would catch some
product malfunctions in the field.
 
Cheers,

Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck