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+>CPU Load Measurements</TITLE
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+><H1
+><A
+NAME="CPULOAD-FUNCTIONS">Chapter 51. CPU Load Measurements</H1
+><DIV
+CLASS="SECT1"
+><H1
+CLASS="SECT1"
+><A
+NAME="SERVICES-CPULOAD-API">CPU Load API</H1
+><P
+>The package allows the CPU load to be estimated. The measurement code
+must first be calibrated to the target it is running on. Once this
+has been performed the measurement process can be started. This is a
+continuous process, so always providing the most up to data
+measurements. The process can be stopped at any time if required. Once
+the process is active, the results can be retrieved.</P
+><P
+>Note that if the target/processor performs any power saving actions,
+such as reducing the clock speed, or halting until the next interrupt
+etc, these will interfere with the CPU load measurement. Under these
+conditions the measurement results are undefined. The synthetic target
+is one such system. See the implementation details at the foot of this
+page for further information. </P
+><P
+>SMP systems are not supported, only uniprocessor system.</P
+><P
+> The API for load measuring functions can be
+found in the file <TT
+CLASS="FILENAME"
+>cyg/cpuload/cpuload.h</TT
+>.</P
+><DIV
+CLASS="SECT2"
+><H2
+CLASS="SECT2"
+><A
+NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-CALIBRATE">cyg_cpuload_calibrate</H2
+><P
+>This function is used to calibrate the cpu load measurement code. It
+makes a measurement to determine the CPU properties while idle.</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>void cyg_cpuload_calibrate(cyg_uint32 *calibration);</PRE
+></TD
+></TR
+></TABLE
+><P
+>The function returns the calibration value at the location pointed to
+by <TT
+CLASS="PARAMETER"
+><I
+>calibration</I
+></TT
+>.</P
+><P
+>This function is quite unusual. For it to work correctly a few
+conditions must be met. The function makes use of the two highest
+thread priorities. No other threads must be using these priorities
+while the function is being used. The kernel scheduler must be started
+and not disabled. The function takes 100ms to complete during which
+time no other threads will be run.</P
+></DIV
+><DIV
+CLASS="SECT2"
+><H2
+CLASS="SECT2"
+><A
+NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-CREATE">cyg_cpuload_create</H2
+><P
+>This function starts the CPU load measurments.</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>void cyg_cpuload_create(cyg_cpuload_t *cpuload,
+ cyg_uint32 calibrate,
+ cyg_handle_t *handle);</PRE
+></TD
+></TR
+></TABLE
+><P
+>The measurement process is started and a handle to it is returned in
+<TT
+CLASS="PARAMETER"
+><I
+>*handle</I
+></TT
+>. This handle is used to access the
+results and the stop the measurement process. </P
+></DIV
+><DIV
+CLASS="SECT2"
+><H2
+CLASS="SECT2"
+><A
+NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-DELETE">cyg_cpuload_delete</H2
+><P
+>This function stops the measurement process. </P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>void cyg_cpuload_delete(cyg_handle_t handle);</PRE
+></TD
+></TR
+></TABLE
+><P
+><TT
+CLASS="PARAMETER"
+><I
+>handle</I
+></TT
+> should be the value returned by the create function.</P
+></DIV
+><DIV
+CLASS="SECT2"
+><H2
+CLASS="SECT2"
+><A
+NAME="SERVICES-CPULOAD-API-CYG-CPULOAD-GET">cyg_cpuload_get</H2
+><P
+>This function returns the latest measurements.</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>void cyg_cpuload_get(cyg_handle_t handle,
+ cyg_uint32 *average_point1s,
+ cyg_uint32 *average_1s,
+ cyg_uint32 *average_10s);</PRE
+></TD
+></TR
+></TABLE
+><P
+><TT
+CLASS="PARAMETER"
+><I
+>handle</I
+></TT
+> should be the value returned by the
+create function. The load measurements for the last 100ms, 1s and 10s
+are returned in
+<TT
+CLASS="PARAMETER"
+><I
+>*average_point1s</I
+></TT
+>,<TT
+CLASS="PARAMETER"
+><I
+>*average_1s</I
+></TT
+>
+and <TT
+CLASS="PARAMETER"
+><I
+>*average_10s</I
+></TT
+> respectively.</P
+></DIV
+><DIV
+CLASS="SECT2"
+><H2
+CLASS="SECT2"
+><A
+NAME="SERVICES-CPULOAD-API-IMPLEMENTATION">Implementation details</H2
+><P
+>This section gives a few details of how the measurements are
+made. This should help to understand what the results mean.</P
+><P
+>When there are no other threads runnable, eCos will execute the idle
+thread. This thread is always runnable and uses the lowest thread
+priority. The idle thread does little. It is an endless loop which
+increments the variable, <TT
+CLASS="LITERAL"
+>idle_thread_loops</TT
+> and
+executes the macro <TT
+CLASS="LITERAL"
+>HAL_IDLE_THREAD_ACTION</TT
+>. The cpu
+load measurement code makes use of the variable. It periodically
+examines the value of the variable and sees how much it has
+changed. The idler the system, the more it will have incremented. From
+this it is simple to determine the load of the system.</P
+><P
+>The function <TT
+CLASS="LITERAL"
+>cyg_cpuload_calibrate</TT
+> executes the
+idle thread for 100ms to determine how much
+<TT
+CLASS="LITERAL"
+>idle_thread_loops</TT
+> is incremented on a system idle
+for 100ms. <TT
+CLASS="LITERAL"
+>cyg_cpuload_create</TT
+> starts an alarm which
+every 100ms calls an alarm function. This function looks at the
+difference in <TT
+CLASS="LITERAL"
+>idle_thread_loops</TT
+> since the last
+invocation of the alarm function and so calculated how idle or busy
+the system has been. The structure <TT
+CLASS="LITERAL"
+>cyg_cpuload</TT
+> is
+updated during the alarm functions with the new results. The 100ms
+result is simply the result from the last measurement period. A simple
+filter is used to average the load over a period of time, namely 1s
+and 10s. Due to rounding errors, the 1s and 10s value will probably
+never reach 100% on a fully loaded system, but 99% is often seen.</P
+><P
+>As stated above, clever power management code will interfere with
+these measurements. The basic assumption is that the idle thread will
+be executed un-hindered and under the same conditions as when the
+calibration function was executed. If the CPU clock rate is reduced,
+the idle thread counter will be incremented less and so the CPU load
+measurements will give values too high. If the CPU is halted entirely,
+100% cpu load will be measured.</P
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