Comtrol eCos - Manual (Page 64)

Alarms
Alarms can be temporarily disabled and reenabled using cyg_alarm_disable and cyg_alarm_enable . Alter-
natively another call to cyg_alarm_initialize can be used to modify the behaviour of an existing alarm. If an
alarm is no longer required then the associated resources can be released using cyg_alarm_delete .
The alarm function is invoked when a counter tick occurs, in other words when there is a call to
cyg_counter_tick , and will happen in the same context. If the alarm is associated with the system’s real-time
clock then this will be DSR context, following a clock interrupt. If the alarm is associated with some other
application-specific counter then the details will depend on how that counter is updated.
If two or more alarms are registered for precisely the same counter tick, the order of execution of the alarm functions
is unspecified.
Valid contexts
cyg_alarm_create cyg_alarm_initialize is typically called during system initialization but may
also be called in thread context. The same applies to cyg_alarm_delete . cyg_alarm_initialize ,
cyg_alarm_disable and cyg_alarm_enable may be called during initialization or from thread or DSR
context, but cyg_alarm_enable and cyg_alarm_initialize may be expensive operations and should only be
called when necessary.
64