+++ /dev/null
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-<HTML
-><HEAD
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->Counters</TITLE
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-TITLE="Exception handling"
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-TITLE="Clocks"
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-><H1
-><A
-NAME="KERNEL-COUNTERS">Counters</H1
-><DIV
-CLASS="REFNAMEDIV"
-><A
-NAME="AEN854"
-></A
-><H2
->Name</H2
->cyg_counter_create, cyg_counter_delete, cyg_counter_current_value, cyg_counter_set_value, cyg_counter_tick -- Count event occurrences</DIV
-><DIV
-CLASS="REFSYNOPSISDIV"
-><A
-NAME="AEN861"><H2
->Synopsis</H2
-><DIV
-CLASS="FUNCSYNOPSIS"
-><A
-NAME="AEN862"><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_counter_create</CODE
->(cyg_handle_t* handle, cyg_counter* counter);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_counter_delete</CODE
->(cyg_handle_t counter);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->cyg_tick_count_t cyg_counter_current_value</CODE
->(cyg_handle_t counter);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_counter_set_value</CODE
->(cyg_handle_t counter, cyg_tick_count_t new_value);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_counter_tick</CODE
->(cyg_handle_t counter);</CODE
-></P
-><P
-></P
-></DIV
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="KERNEL-COUNTERS-DESCRIPTION"
-></A
-><H2
->Description</H2
-><P
->Kernel counters can be used to keep track of how many times a
-particular event has occurred. Usually this event is an external
-signal of some sort. The most common use of counters is in the
-implementation of clocks, but they can be useful with other event
-sources as well. Application code can attach <A
-HREF="kernel-alarms.html"
->alarms</A
-> to counters, causing a function
-to be called when some number of events have occurred.
- </P
-><P
->A new counter is initialized by a call to
-<TT
-CLASS="FUNCTION"
->cyg_counter_create</TT
->. The first argument is used to
-return a handle to the new counter which can be used for subsequent
-operations. The second argument allows the application to provide the
-memory needed for the object, thus eliminating any need for dynamic
-memory allocation within the kernel. If a counter is no longer
-required and does not have any alarms attached then
-<TT
-CLASS="FUNCTION"
->cyg_counter_delete</TT
-> can be used to release the
-resources, allowing the <SPAN
-CLASS="STRUCTNAME"
->cyg_counter</SPAN
-> data
-structure to be re-used.
- </P
-><P
->Initializing a counter does not automatically attach it to any source
-of events. Instead some other code needs to call
-<TT
-CLASS="FUNCTION"
->cyg_counter_tick</TT
-> whenever a suitable event
-occurs, which will cause the counter to be incremented and may cause
-alarms to trigger. The current value associated with the counter can
-be retrieved using <TT
-CLASS="FUNCTION"
->cyg_counter_current_value</TT
-> and
-modified with <TT
-CLASS="FUNCTION"
->cyg_counter_set_value</TT
->. Typically
-the latter function is only used during initialization, for example to
-set a clock to wallclock time, but it can be used to reset a counter
-if necessary. However <TT
-CLASS="FUNCTION"
->cyg_counter_set_value</TT
-> will
-never trigger any alarms. A newly initialized counter has a starting
-value of 0.
- </P
-><P
->The kernel provides two different implementations of counters. The
-default is <TT
-CLASS="VARNAME"
->CYGIMP_KERNEL_COUNTERS_SINGLE_LIST</TT
-> which
-stores all alarms attached to the counter on a single list. This is
-simple and usually efficient. However when a tick occurs the kernel
-code has to traverse this list, typically at DSR level, so if there
-are a significant number of alarms attached to a single counter this
-will affect the system's dispatch latency. The alternative
-implementation, <TT
-CLASS="VARNAME"
->CYGIMP_KERNEL_COUNTERS_MULTI_LIST</TT
->,
-stores each alarm in one of an array of lists such that at most one of
-the lists needs to be searched per clock tick. This involves extra
-code and data, but can improve real-time responsiveness in some
-circumstances. Another configuration option that is relevant here
-is <TT
-CLASS="VARNAME"
->CYGIMP_KERNEL_COUNTERS_SORT_LIST</TT
->, which is
-disabled by default. This provides a trade off between doing work
-whenever a new alarm is added to a counter and doing work whenever a
-tick occurs. It is application-dependent which of these is more
-appropriate.
- </P
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="KERNEL-COUNTERS-CONTEXT"
-></A
-><H2
->Valid contexts</H2
-><P
-><TT
-CLASS="FUNCTION"
->cyg_counter_create</TT
-> is typically called during
-system initialization but may also be called in thread context.
-Similarly <TT
-CLASS="FUNCTION"
->cyg_counter_delete</TT
-> may be called during
-initialization or in thread context.
-<TT
-CLASS="FUNCTION"
->cyg_counter_current_value</TT
->,
-<TT
-CLASS="FUNCTION"
->cyg_counter_set_value</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_counter_tick</TT
-> may be called during
-initialization or from thread or DSR context. In fact,
-<TT
-CLASS="FUNCTION"
->cyg_counter_tick</TT
-> is usually called from inside a
-DSR in response to an external event of some sort.
- </P
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