exit function when interrupted

I have an interrupt function called, interrupt_Foo() {...} which turns on a flag when 1 second has elapsed, and a user-defined function foo_calling() {...} which calls another function foo_called() {...}. I want to stop the process in foo_called() when 1 second has elapsed.

The code snippet below may elaborate further my need:

void interrupt interrupt_foo() {
   ...
   if(1 second has elapsed) {
      flag1s = 1;
   } else {
      flag1s = 0;
   }
}

void foo_calling() {
   // need som开发者_运维技巧ething here to stop the process of foo_called()
   ...
   (*fptr_called)(); // ptr to function which points to foo_called
   ...
}

void foo_called() {
   // or something here to stop the process of this function
   ...
   // long code
   ...
}

This is real time operating system so polling the 1 second flag inside foo_called() at some portion in the code is undesirable. Please help.

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If you are willing to write non-portable code, and test the heck out of it before deploying it, and if the processor supports it, there may be a solution.

When the interrupt handler is called, the return address must be stored somewhere. If that is a location your code can query - like a fixed offset down the stack - then you can compare that address to the range occupied by your function to determine if 'foo_called is executing. You can get the address of the function by storing a dummy address, compiling, parsing the map file, then updating the address and recompiling.

Then, if your processor supports it, you can replace the return address with the address of the last instruction(s) of foo_called. (make sure you include the stack cleanup and register restoration code.). Then exit the interrupt as normal, and the interrupt handling logic will return code to the end of your interrupted function.

If the return address is not stored in the stack, but in an unwritable register, you still may be able to force quit your function - if the executable code is in writrable memory. Just store the instruction at the interruupt's return address, then overwrite it with a jump instruction which jumps to the function end. In the caller code, add a detector which restored the overwritten instruction.

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I would expect that your RTOS has some kind of timer signal/interrupt that you can use to notify you when one second has passed. For instance if it is a realtime UNIX/Linux then you would set a signal handler for SIGALRM for one second. On a RT variant of Linux this signal will have more granularity and better guarantees than on a non-RT variant. But it is still a good idea to set the signal for slightly less than a second and busy-wait (loop) until you reach one second.