Query :Regarding Synthesis Report

At the fourth line of the report, there is mention about CPU time and Elapsed time. Similarly at the end of the report, just before the message total memory usage, there is again mention about another CPU time and Elapsed time. I would like to know precisely what do these two times mean and what can be interpreted from them for a particular HDL program. Do they carry significance ?

--Starting of the report --

Release 8.2i - xst I.31 Copyright (c) 1995-2006 Xilinx, Inc. All rights reserved.

--> Parameter TMPDIR set to ./xst/projnav.tmp CPU : 0.00 / 5.14 s | Elapsed : 0.00 / 5.00 s

--> Parameter xsthdpdir set to ./xst CPU : 0.00 / 5.14 s | Elapsed : 0.00 / 5.00 s

--> Reading design: fsopform.prj

--End of Report --

========================================================================= CPU : 15.02 / 20.44 s | Elapsed : 15.00 / 21.00 s

Hello,

The elapsed time is what you experience and can measure on your watch (namely, how long you had to wait, in seconds, for completion).

The CPU time is a measure of how long the CPU was actually executing instructions related to completing the task. In a multitasking environment, your application is not the only application that is "running". You can see this in the Windows task manager, or by using a command like "top" on a unix machine.

The difference between the elapsed time and the CPU time is time the CPU spent executing other applications, and I believe it also includes overhead from application context switching. I'm not sure how the time spent waiting on I/O (e.g. disk or network access) is accounted for.

These values, along with the "Total memory usage is ..." statistic, are not directly relevant to digital logic design, and not generally useful to me except when trying to figure out:

1. Why I had to wait longer than expected (was it the task, or the CPU load?) Obviously, this never happens! ;)
2. If my computer is in need of a memory upgrade.

Eric