Switching between modes with an interrupt - c

Question

I have two modes that I want to switch between with an interrupt that is generated by a sliding switch. Initially I read the current position and choose a mode/function. I want to switch between the two right when the position of the switch is changed. I have an interrupt which occurs on both edges (whenever the position is changed). However since both functions run continuously in a while loop, I can't just call them in the interrupt. Basically I have something like this:
interrupt()
{
//not sure how to switch between modes here
}
main()
{
//choose mode on startup
if (switch_HIGH)
modeA();
else
modeB();
}
modeA()
{
while(1)
{
//do something
}
}
modeB()
{
while(1)
{
//do something
}
}
I don't know if it's a good idea to just leave a function where it is and just move to something else but I can't think of any other way to do it. I'd really appreciate it if someone could tell me how I can go about this.
The language I'm using is C and the platform is a NIOS system on a Altera DE1 development board.

Answer 1

Using an interrupt for this seems very pointless; it's much simpler to just poll the input on each loop, and call the proper function just as you're doing.
UPDATE: I just relized your code doesn't have a loop, so the above is a bit hard to understand, of course.
I meant that you can structure your program like this:
int main(void)
{
initialize_hardware();
while(1)
{
if(switch_HIGH)
modeA();
else
modeB();
}
}
This makes the CPU go around in an infinite loop, and on each iteration it checks the switch and calls either modeA() or modeB() depending on the current mode.
Adding an interrupt gains you nothing except adding more complexity.
That said, what I would do is use a function pointer to indicate the current mode, and change the function pointer's value inside the interrupt, depending on the state of the switch. Then in the main loop just call the pointed-at function.
Remember to initialize the function properly, since you probably won't get an interrupt when teh device comes out of reset. This is another argument against this solution; the complexity is much bigger than just checking the switch on each iteration.

Answer 2

How about calling the two functions as threads. The interrupt function can kill the active thread and start the other thread. Pseudo code:
thread threada,threadb;
flag a=0;
interrupt()
{
if(a==0)
{
thread_kill(threada);
threadb=thread_create(modeB);
a=1;
}
else
{
thread_kill(threadb);
threada=thread_create(modeA);
a=0;
}
}
main()
{
thread_create(threada);
a=1;
}
modeA()
{
while(1)
{
//do something
}
}
modeB()
{
while(1)
{
//do something
}
}
Rather than killing the thread, you can have graceful shutdown mechanism using some kind of synchronization.