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Update time command description in the NSH document

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Gregory Nutt 2016-01-01 09:10:21 -06:00
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Documentation/NuttShell.html
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@ -2642,7 +2642,7 @@ time "<command>"
Perform command timing. Perform command timing.
This command will execute the following <command> string and then show how much time was required to execute the command. This command will execute the following <command> string and then show how much time was required to execute the command.
Time is shown with a resolution of 100 microseconds which may be beyond the resolution of many configurations. Time is shown with a resolution of 100 microseconds which may be beyond the resolution of many configurations.
Note that the <command> string must be enclosed in quotation marks. Note that the <command> must be enclosed in quotation marks if it contains spaces or other delimiters.
</p> </p>
<p><b>Example:</b></p> <p><b>Example:</b></p>
<ul><pre> <ul><pre>
@ -2654,7 +2654,13 @@ nsh&gt;
<p> <p>
The additional 10 millseconds in this example is due to the way that the sleep command works: It always waits one system clock tick longer than requested and this test setup used a 10 millisecond periodic system The additional 10 millseconds in this example is due to the way that the sleep command works: It always waits one system clock tick longer than requested and this test setup used a 10 millisecond periodic system
timer. timer.
Sources of error could include the additional overhead of the time command execution itself which is included in the total and various quantization errors. Sources of error could include various quantization errors, competing CPU usage, and the additional overhead of the time command execution itself which is included in the total.
</p>
<p>
The reported time is the elapsed time from starting of the command to completion of the command.
This elapsed time may not necessarily the processing time for the command.
In a busy system, command processing could be delayed if pre-empted by other, higher priority threads competing for CPU time.
So the reported time includes all CPU processing from the start of the command to its finish possibly including unrelated processing time during that interval.
</p> </p>
<p> <p>
Notice that: Notice that: