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TASK
FUNCTION
A µexec task is a C function
that does not take an argument or return a result.
Any such function can be made into a task via UEXC_CreateTask.
Tasks can be created
and killed dynamically, even within other tasks. Normally,
a task function should not terminate (i.e., it should
execute an infinite loop). If it does, µexec deletes
it from the internal data structures.
Typically, you create
some tasks in your main routine and then start the
scheduler running. After that, the processor executes
your tasks and never returns to the main routine.
Each task needs its own
stack, which is supplied to the system when a task
is created. Unfortunately, stack overrun (i.e., when
a task uses stack space that is beyond the range of
the supplied stack) can be a deadly problem.
µexec checks the stack
pointer of a task to ensure that it’s within
bounds, but this check may not be of much value since
a stack overrun may have already damaged important
data, including µexec’s internal data structures.
So, it’s best to be conservative and allocate
a large stack for a task. In fact, if your system
crashes mysteriously, try allocating larger stacks
for your tasks.
Stack overrun is a general
problem in embedded programs. Multiple tasks exacerbate
the problem because each task uses its own stack.
If there is only one control loop, then all the functions
execute with one stack and it is easier to be conservative
with just that stack. Unfortunately, you have to pay
the price for using a multitasking executive.
