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Development System Reference Guide www.xilinx.com 387
Netlist Launcher (Netlister)
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When NGDBuild is invoked, the Netlist launcher goes through the following steps:
1. The Netlist Launcher initializes itself with a set of rules for determining what netlist
reader to use with each type of netlist, and the options with which each reader is
invoked.
The rules are contained in the system rules file (described in “System Rules File”) and
in the user rules file (described in “User Rules File”).
2. NGDBuild makes the directory of the top-level netlist the first entry in the Netlist
Launcher’s list of search paths.
3. For the top-level design and for each file referenced in the top-level design, NGDBuild
queries the Netlist Launcher for the presence of the corresponding NGO file.
4. For each NGO file requested, the Netlist Launcher performs the following actions:
♦ Determines what netlist is the source for the requested NGO file
The Netlist Launcher determines the source netlist by looking in its rules database
for the list of legal netlist extensions. Then, it looks in the search path (which
includes the current directory) for a netlist file possessing a legal extension and the
same name as the requested NGO file.
♦ Finds the requested NGO file
The Netlist Launcher looks first in the directory specified with the –dd option (or
current directory if a directory is not specified). If the NGO file is not found there
and the source netlist was not found in the search path, the Netlist Launcher looks
for the NGO file in the search path.
♦ Determines whether the NGO file must be created or updated
If neither the netlist source file nor the NGO file is found, NGDBuild exits with an
error.
If the netlist source file is found but the corresponding NGO file is not found, the
Netlist Launcher invokes the proper netlist reader to create the NGO file.
If the netlist source file is not found but the corresponding NGO file is found, the
Netlist Launcher indicates to NGDBuild that the file exists and NGDBuild uses
this NGO file.
If both the netlist source file and the corresponding NGO file are found, the netlist
file’s time stamp is checked against the NGO file’s timestamp. If the timestamp of
the NGO file is later than the source netlist, the Netlist Launcher returns a “found”
status to NGDBuild. If the timestamp of the NGO file is earlier than the netlist
source, or the NGO file is not present in the expected location, then the Launcher
creates the NGO file from the netlist source by invoking the netlist reader specified
by its rules.
Note:
The timestamp check can be overridden by options on the NGDBuild command line. The
–nt on option updates all existing NGO files, regardless of their timestamps. The –nt off option
does not update any existing NGO files, regardless of their timestamps.
5. The Netlist launcher indicates to NGDBuild that the requested NGO files have been
found, and NGDBuild can process all of these NGO files.