Hi,
I feel quite foolish asking the following question... Please don't judge me too
harshly...
In my MSPGCC based system I have got the following #defines which I use for
critical (interrupts disabled) access around volatile memory which is modified
by interrupt routines:
#define criticalStart() __asm__ __volatile__("push r2"::); __asm__
__volatile__("dint"::)
#define criticalEnd() __asm__ __volatile__("pop r2"::)
Usually I use this code to write to a counter which is decremented by my timer
ISR, eg
void setTimeout(UInt16 timeout)
{
// Other work before setting the volatile, ISR driven value
criticalStart();
busyTimeout = timeout;
criticalEnd();
}
Today I am using Code composer for a new project and I tried a similar trick.
After several hours of debugging, it turns out that my little "push r2" trick
causes code composer to access local variables incorrectly, since these are
accessed relative to the stack pointer.
For example, the following code does not function correctly because the
"localTimer" variable is not written correctly (the memory access is one word
off owing to the extra stack push).
while(true)
{
UInt32 localTimer;
criticalStart();
localTimer = globalTimer;
criticalEnd();
if (localTimer == 0)
{
break;
}
}
My question is, does GCC analyse the inline assembly code and notice that I
have altered the stack, or have I just been *extremely* lucky for many years?
Certainly code composer does not see that I have modified the stack.
I am going to change my critical macros like so (this is how I am now doing
critical access in code composer, which, unless I am missing something, has no
builtin way to do critical functions):
#define criticalStart() { UInt16 __oldInterruptStatus__ = READ_SR(); __asm__
__volatile__("dint"::)
#define criticalEnd() WRITE_SR(__oldInterruptStatus__); }
Any major issues with doing this? Should I instead wrap all reads and writes to
volatile memory/variables with critical functions? I usually only wrap one line
of code with the critical macros.
Also if anybody knows code composer v3.1 and knows a better way, please let me
know.
Thanks,
- Wayne
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