Is there a mechanism in the scheduler to fire a task at a specific
interval, where the task execution time itself might be variable and
'os_time_delay' might not work.
For example, assume we need to fire the task reliably at 50hz (within
scheduler limits) then push data into a time sensitive algorithm, but
the task workload has a variable execution time. This won't work:
void my_task_func(void *arg) {
/* The task is a forever loop that does not return */
while (1) {
/* Sample data at 50Hz */
os_time_delay( OS_TICKS_PER_SEC/50);
/* Variable time task to get data */
do_something_with_variable_delay()
}
}
If we knew the time for 'do_something' this would be easy, but if not we
need to get the timestamp before execution, and then delay for the
required timespan minus execution time, taking into account timer
rollover, task overrun, etc. That doesn't seem very elegant.
I was wondering if some mechanism to do something like this exists
already in the system, perhaps in another form like indicating a fixed
delay when the task is created:
void my_50hz_func(void *arg) {
static uint32_t a, b;
while (1) {
a = GET_CURRENT_TIMESTAMP; /* Imaginary macro for discussion
purposes! */
/* Variable time task to get data */
do_something_with_variable_delay()
/* Delay until the 20ms interval has passed */
*os_time_delay_until(a + OS_TICKS_PER_SEC/50);**
*** }
}
Alternatively if something like delay_until is a bad approach (?), can
you initialize a task somehow with a fixed delay, saying fire this every
20ms for example, and then just put the task to sleep once the read is
done and you've sent the data to the time sensitive algorithm?
Sorry if I'm missed something obvious looking through the scheduler,
task and time documentation.
