Vision VHD-800 Specifikace stáhnout pdf (Strana 19)

8 Synthesis Hints

Throughout this section, some useful hints with regard to synthesis will be given. They may help you during this exercise

or during one of your future VLSI projects.

8.1 DesignVision

Command echoing The command echoing feature in the GUI is useful to become familiar with the SYNOPSYS DESIGN

COMPILER command syntax. Use the history command in order to see a list of all previously executed commands.

A script ﬁle can be generated by history -h > scripts/scriptfile.tcl. This ﬁle may then be edited and

run by means of the command source or the menu option File→Execute Script....

Graphical interface Most of the SYNOPSYS DESIGN COMPILER commands are available via the menu driven graphical

interface. However, some of the more versatile commands and speciﬁc command options have to be entered in

textual form. Use the help command to see a list of available commands.

Command option Most command options can be abbreviated to their shortest equivalent form (e.g., -h for -hierarchy,

. . . ). There have been some cases, where the full option worked but the abbreviated form did not work, however.

Commands response A successfully executed command is signaled by a 1 at the end of the associated report. A 0

indicates that the command failed. Be aware that certain commands (like analyzing a design ﬁle with more than

one design unit) involve multiple actions each of which is attributed a 1 or 0. Always apply yourself to the reports

generated and note any warnings issued by SYNOPSYS DESIGN COMPILER.

8.2 DC Shell

Startup The more you will use SYNOPSYS DESIGN COMPILER, the less you will use the GUI version of it. Starting the DC

Shell always from the cockpit may become annoying, because you have to start the cockpit ﬁrst. Instead, you can

run the DC Shell from a UNIX shell using the command synopsys dc_shell-xg-t.

Manpages If you are looking for a certain command argument, but cannot remember the exact syntax, just have a look at

the manpage of the respective command (e.g., man create_clock). This deﬁnitely works out faster than browsing

through hundreds of pages within the SYNOPSYS DESIGN COMPILER manual, looking for the respective command.

8.3 Warnings

Warning and error messages: Synopsys can be very talkative. Sometimes you get buried in information, warning, and

error messages. Nevertheless, you should try to understand all these messages and not just ignore them. Often they

contain valuable hints and information, pointing to possible design problems or ﬂaws.

Old data: Beware of old data lying around and causing problems. This might be data in the SYNOPSYS DESIGN COMPILER

memory, in design libraries or .ddc ﬁles on your search path. If you think your changes aren’t included or get

inexplicable problems, try cleaning all old data: remove all designs from memory, remove all ﬁles in your design

libraries and remove any unneeded .ddc ﬁle, especially in your working directory. It might be a good idea to save .ddc

ﬁles to a directory that is not on the SYNOPSYS DESIGN COMPILER’s search path, except for the ones you speciﬁcally

want to be included (use list search_path to check your path).

8.4 Design Objects

Cells & instances: SYNOPSYS DESIGN COMPILER does not make use of the terms cell and instance in a consistent way.

In general, they can be conceived to be synonyms in the context of SYNOPSYS DESIGN COMPILER.

Locate: To locate speciﬁc design objects in the schematic view use the menu entry Select→By Name.... In the com-

mand mode you can identify speciﬁc design objects by means of the find and filter commands.

Find: For ﬁnding all design objects of a particular type, shorthand commands exists (e.g., all_inputs, all_outputs,

all_registers).

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