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-<HTML
-><HEAD
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->Alarms</TITLE
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-><H1
-><A
-NAME="KERNEL-ALARMS">Alarms</H1
-><DIV
-CLASS="REFNAMEDIV"
-><A
-NAME="AEN1016"
-></A
-><H2
->Name</H2
->cyg_alarm_create, cyg_alarm_delete, cyg_alarm_initialize, cyg_alarm_enable, cyg_alarm_disable -- Run an alarm function when a number of events have occurred</DIV
-><DIV
-CLASS="REFSYNOPSISDIV"
-><A
-NAME="AEN1023"><H2
->Synopsis</H2
-><DIV
-CLASS="FUNCSYNOPSIS"
-><A
-NAME="AEN1024"><P
-></P
-><TABLE
-BORDER="5"
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-><TR
-><TD
-><PRE
-CLASS="FUNCSYNOPSISINFO"
->#include <cyg/kernel/kapi.h>
- </PRE
-></TD
-></TR
-></TABLE
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_alarm_create</CODE
->(cyg_handle_t counter, cyg_alarm_t* alarmfn, cyg_addrword_t data, cyg_handle_t* handle, cyg_alarm* alarm);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_alarm_delete</CODE
->(cyg_handle_t alarm);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_alarm_initialize</CODE
->(cyg_handle_t alarm, cyg_tick_count_t trigger, cyg_tick_count_t interval);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_alarm_enable</CODE
->(cyg_handle_t alarm);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_alarm_disable</CODE
->(cyg_handle_t alarm);</CODE
-></P
-><P
-></P
-></DIV
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="KERNEL-ALARMS-DESCRIPTION"
-></A
-><H2
->Description</H2
-><P
->Kernel alarms are used together with counters and allow for action to
-be taken when a certain number of events have occurred. If the counter
-is associated with a clock then the alarm action happens when the
-appropriate number of clock ticks have occurred, in other words after
-a certain period of time.
- </P
-><P
->Setting up an alarm involves a two-step process. First the alarm must
-be created with a call to <TT
-CLASS="FUNCTION"
->cyg_alarm_create</TT
->. This
-takes five arguments. The first identifies the counter to which the
-alarm should be attached. If the alarm should be attached to the
-system's real-time clock then <TT
-CLASS="FUNCTION"
->cyg_real_time_clock</TT
->
-and <TT
-CLASS="FUNCTION"
->cyg_clock_to_counter</TT
-> can be used to get hold
-of the appropriate handle. The next two arguments specify the action
-to be taken when the alarm is triggered, in the form of a function
-pointer and some data. This function should take the form:
- </P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->void
-alarm_handler(cyg_handle_t alarm, cyg_addrword_t data)
-{
- …
-}
- </PRE
-></TD
-></TR
-></TABLE
-><P
->The data argument passed to the alarm function corresponds to the
-third argument passed to <TT
-CLASS="FUNCTION"
->cyg_alarm_create</TT
->.
-The fourth argument to <TT
-CLASS="FUNCTION"
->cyg_alarm_create</TT
-> is used
-to return a handle to the newly-created alarm object, and the final
-argument provides the memory needed for the alarm object and thus
-avoids any need for dynamic memory allocation within the kernel.
- </P
-><P
->Once an alarm has been created a further call to
-<TT
-CLASS="FUNCTION"
->cyg_alarm_initialize</TT
-> is needed to activate it.
-The first argument specifies the alarm. The second argument indicates
-the number of events, for example clock ticks, that need to occur
-before the alarm triggers. If the third argument is 0 then the alarm
-will only trigger once. A non-zero value specifies that the alarm
-should trigger repeatedly, with an interval of the specified number of
-events.
- </P
-><P
->Alarms can be temporarily disabled and reenabled using
-<TT
-CLASS="FUNCTION"
->cyg_alarm_disable</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_alarm_enable</TT
->. Alternatively another call to
-<TT
-CLASS="FUNCTION"
->cyg_alarm_initialize</TT
-> 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
-<TT
-CLASS="FUNCTION"
->cyg_alarm_delete</TT
->.
- </P
-><P
->The alarm function is invoked when a counter tick occurs, in other
-words when there is a call to <TT
-CLASS="FUNCTION"
->cyg_counter_tick</TT
->,
-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.
- </P
-><P
->If two or more alarms are registered for precisely the same counter tick,
-the order of execution of the alarm functions is unspecified.
- </P
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="KERNEL-ALARMS-CONTEXT"
-></A
-><H2
->Valid contexts</H2
-><P
-><TT
-CLASS="FUNCTION"
->cyg_alarm_create</TT
->
-<TT
-CLASS="FUNCTION"
->cyg_alarm_initialize</TT
-> is typically called during
-system initialization but may also be called in thread context. The
-same applies to <TT
-CLASS="FUNCTION"
->cyg_alarm_delete</TT
->.
-<TT
-CLASS="FUNCTION"
->cyg_alarm_initialize</TT
->,
-<TT
-CLASS="FUNCTION"
->cyg_alarm_disable</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_alarm_enable</TT
-> may be called during
-initialization or from thread or DSR context, but
-<TT
-CLASS="FUNCTION"
->cyg_alarm_enable</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_alarm_initialize</TT
-> may be expensive operations
-and should only be called when necessary.
- </P
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