All,
I am trying to track down a problem of some code that was written by an 'overseas' 3rd party (I will be nice and not state the country of origin).
This code uses a single timer set at a 1mS interrupt rate in order to determine if the SPI is still communicating externally with it's master. If no communications are detected the timer resets the SPI port, clears the interrupt, and jumps to the reset vector. The problem is: the SPI port remains dead until a power cycle is accomplished.
The obvious fix is to use the watchdog (which is what I will eventually do), but I would like to understand the why of why this does not work (yes, bad coding practice is the real reason)...
Since the code jumps to the reset vector this is what I have been able to analyze:
(1) Since this is not a true reset (ie: via watchdog) all hardware registers are not reset - problem potential here. (2) The jump to the reset vector was accomplished while in supervisor mode, so the privleged registers (ie: SP,etc) can be written. (3) The timer interrupt was cleared prior to making the jump to the reset vector, so all interrupts are still enabled. (4) Since this is not a true reset, all resident code can still execute (ie: interrupt handlers). (5) The startup code will reset all initialized data, registers, etc prior to jumping to program main(), effectively returning data to a power up state.
One reason I can currently come up with as to why the SPI is never functional after this occurs is that maybe an interrupt occurs while in the startup code (clearing a tracking variable or resetting the processor registers). But the interrupt would also inhibit the startup code until it was serviced. This potential cause is (probably) not the only reason for this issue, and why I am asking for your input(s).
Unfortunately, this board has no JTAG to connect so stepping through the code is not an option. I could write to the serial port - if it was connected, but it isnt. Right now I am trying to analyze my way through this code before using a 'hammer' approach to solving this problem.
What else am I missing in this analysis? Thanks.
The funny thing here is that the "volatile" keyword is known to be one of the most problematic for compilers. Not just in efficiency, but in producing broken code. www.cs.utah.edu/.../emsoft08-preprint.pdf
A good link about volatile: blog.regehr.org/.../28
Found these gems associated to the name of this thread (credit to the authors). Applicability is in the readers eyes:
"The infinite monkey theorem states that a monkey hitting keys at random on a typewriter keyboard for an infinite amount of time will almost surely type a given text, such as the complete works of William Shakespeare."
Better yet:
"Would a million rednecks shooting at road signs ultimately produce the entire works of Shakespeare in braille?"
Per,
Didnt want to 'cross this bridge' in the original post as most of the responses to this 'structuring' (used very loosely here - actually probably the wrong description altogether) would have probably masked the original question(s) I was trying to get answered above.
After reading the abstract to the first link I must take the time now to stop and read this information to conclusion prior to resuming my other functions (I guess it was also for me so as not to get waylayed).
Good, informational links though.
Thanks.