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Xilinx Synthesis Technology User Guide

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XST <strong>User</strong> <strong>Guide</strong><br />

Note All messages issued by XST are displayed on the screen only. If<br />

you want to save your messages in a separate log file, then the best<br />

way is to use script mode to launch XST.<br />

In the previous run, XST synthesized entity "stopwatch" as a top level<br />

module of the design. The reason is that this block was placed at the<br />

end of the VHDL file. XST picks up the latest block in the VHDL file<br />

and treats it as a top level one. Suppose you would like to synthesize<br />

just "hex2led" and check its performance independently of the other<br />

blocks. This can be done by specifying the top level entity to<br />

synthesize in the command line using the -ent option (please refer to<br />

Table 8-2 of this chapter for more information):<br />

run -ifn watchvhd.vhd -ifmt VHDL -ofn watchvhd.ngc<br />

-ofmt NGC -p xcv50-bg256-6 -opt_mode Speed<br />

-opt_level 1 -ent hex2led<br />

Script Mode<br />

It can be very tedious work to enter XST commands directly in the<br />

XST shell, especially when you have to specify several options and<br />

execute the same command several times. You can run XST in a script<br />

mode as follows:<br />

1. Open a new file named xst.scr in the current directory. Put the<br />

previously executed XST shell command into this file and save it.<br />

run -ifn watchvhd.vhd -ifmt VHDL -ofn watchvhd.ngc<br />

-ofmt NGC -p xcv50-bg256-6 -opt_mode Speed<br />

-opt_level 1<br />

2. From the tcsh or other shell, enter the following command to start<br />

synthesis.<br />

xst -ifn xst.scr<br />

During this run, XST creates the following files:<br />

• watchvhd.ngc: an NGC file ready for the implementation tools<br />

• xst.srp: the xst script log file<br />

8-16 <strong>Xilinx</strong> Development System

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