This change prevents tickless idle mode potentially sleeping for an extra tick in the corer case that a tick interrupt occurred between the scheduler being suspended and the expected idle time being checked for a second time (within the idle task) - as described by the sequence below. Th change updates eTaskConfirmSleepModeStatus() to specifically check if a tick is pending, and if so, abort entering sleep mode.
+ The idle task decides to enter sleep mode on the following line.
```
if( xExpectedIdleTime >= configEXPECTED_IDLE_TIME_BEFORE_SLEEP )
```
+ The scheduler is suspended, preventing any context switches.
[Potentially a tick interrupt could occur here. That could happen if other tasks executing consumed a lot of time since the above code line executed. If a tick interrupt occurs here the interrupt will be entered but the interrupt will not do anything other than increment xPendedTicks.]
+ The expected idle time is checked again. No context switches can occur now so the code will execute until the scheduler is unsuspended. Assuming configEXPECTED_IDLE_TIME_BEFORE_SLEEP is set to a sensible value, a tick interrupt won't occur for some time.
+ portSUPPRESS_TICKS_AND_SLEEP() is called.
+ The default implementation of the tickless function calls eTaskConfirmSleep() - which prior to this change does not return eAbortSleep even though xPendedTicks is not 0, and after this change does return eAbortSleep.
diff --git a/tasks.c b/tasks.c
index f93fca0..d83db4b 100644
--- a/tasks.c
+++ b/tasks.c
@@ -3526,6 +3526,12 @@
/* A yield was pended while the scheduler was suspended. */
eReturn = eAbortSleep;
}
+ else if( xPendedTicks != 0 )
+ {
+ /* A tick interrupt has already occurred but was held pending
+ because the scheduler is suspended. */
+ eReturn = eAbortSleep;
+ }
else
{
/* If all the tasks are in the suspended list (which might mean they
