Part IIA CBT Project on VLSI Design

VLSI Design/Mentor Resource Page


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Page last updated 20:15 on Monday, 15 May 2006

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new.gif (896 bytes) Your Final Report!

The deadline for the Final Interim Report for the project is Saturday 10th June 5 pm. 

Things you should consider when deciding what to include in the report are mentioned in the FAQ on the Bulletin Board

Handing in your report

  • Note that this is different from the procedure used for first/second reports.
  • Please hand in your report on Saturday 10th June, to Dr Robertson or his deputy in the Entrance Lobby, CUED, between 3 pm and 5 pm
    IMPORTANT - Do not try to hand in your report at any other place in the Department.
  • Please note also the following:-
    You must enclose both previous marked interim reports, securely fastened to your final report.
    Your report must have a completed Feedback Form attached.  Copies should be available at the Enquiries Office on Saturday. 

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new.gif (896 bytes) Colour Printing for ICgraph - all change in 2006!

We have had no real success in making the standard methods for printing out cells work in colour.  This is a real minefield in Mentor and has caused much gnashing of teeth in previous years as well.  However, we do now have a work-around, which has required us to set up an entirely new link to the Department's print infrastructure.  The approach required is therefore quite different from before - but that is not unusual in Mentor, which often offers two or three different ways to accomplish any given task.  Unfortunately, mgcplot cannot be used, and  the new method does not allow for easy image preview before printing, so a little more care is needed - please do not be extravagant in your usage.  It is also available only for colour plots, and for ICgraph - for other tools the standard recipes for monochrome plots, as detailed in the Project Guide, still work fine. 

To generate a colour check plot from ICgraph proceed as follows:

  • With the design you wish open in ICgraph and on the screen with its window activated, give the command: 
    File -> Print -> HotPlot
  • The HotPlot dialogue should appear.  Under Plot Handling select Use Formatter.  
  • Click the Set Formatter Options button, and in the Formatter Only Options dialogue, use the Browser button by the top text box to find and select the Plotcap file, called Plotcap, which is to be found in your cbt directory.  OK the dialogue box.
  • Click the Select Printer button, and select the only available printer "Postscript" that appears in the Select Hotplot Printer dialogue.  OK the dialogue box.
  • Click the Browse button next to the Setup File text box, and use the Select Hotplot Setup File browser to locate and select the file setup.p which is also to be found in your cbt directory. OK the dialogue box.
  • Click the Select Layers button, and in the Print Layers dialogue, with the shift key pressed, select the layers 1 to 17, from n-well down to n-window.  OK the dialogue box.
  • Click the Maximize button, followed by the Compute Plot Size button, then the Scale by Width/Length button.
  • Click the Set Plot Attributes button and in the Hotplot Plot Attributes dialogue that appears, check that Send Plot to Printer is checked.  OK the Hotplot Plot Attributes dialogue, and OK the Hotplot dialogue.  Your plot should be sent to the Colour Laserjet, cljmr1, in the Operators' area.  
  • You may need to experiment with the scaling and rotation parameters to get the best fit of your design to the printed sheet.
  • Note: you can uncheck Send Plot to Printer to have HotPlot create a Postscript file in your cbt directory; typically it will be called rinaxxxx, if your design is called ring_flat or ring_hier, where xxxx is a numeric string; you can preview this using gv rinaxxxx.  This exercise is strongly recommended - zooming in to study key elements (for example, in the ring oscillator, or in an input or output pad driver) is far more practicable on a screen-based image, and will throw much light on the structure.
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Schedule for Week 1

You should aim to complete Lab Guide 1, which introduces the Mentor Falcon Framework and the on-line Help System, as soon as possible.

At the first opportunity read those sections of the project manual covering

You are likely to need most of Tuesday afternoon (and possibly some unscheduled time) to complete Lab Guide 2 - Functional Simulation with ModelSim.

You should aim to complete Lab Guide 3 - Transistor Schematics on Friday morning.

Both Lab 2 and Lab 3 will produce important results which you will need when compiling your First Interim Report.

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VHDL Command syntax

An appendix summarising the syntax for VHDL commands is attached as pages 46-50 at the rear of the section: Hardware Description Language VHDL.   This may help you in Lab Guide 2 - Functional Simulation with ModelSim.  You can see an html version of the command syntax hereThere are sample VHDL files you can inspect here.  Note: these are indicative only and will require adaptation to suit your design.

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Correction to Lab Guide and other documents

Please note the following amendments-

Lab guide

Quick reference leaflet:

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Important News

This year for the VLSI project we shall make use of the twnXX graphics workstations.  This is a major bonus since these workstations offer greater comfort and clearer screens, with large-format TFT displays attached.  Please note the workstations are available to us as follows:-

Tuesday afternoon sessions are scheduled to run from 1.30 pm to 5.30 pm, and we are priority users of the twns during that period.  If you have difficulty finding a seat or are being harassed by others intent on turfing you off during this period, please consult a demonstrator, or if one is not available, the Computer Operators may be able to assist.

If a twnXX is not available you will need to login from one of the other Teaching System workstations - see the handouts and supplementary information below.

The twnXX workstations are high performance PCs running Windows XP  Mentor itself runs on a Unix host.

X-Win32We shall be using the X-win32 X server running on the PCs to access Mentor on tw300 and tw600

Monitoring this page

You are strongly advised to monitor this page, which will be updated regularly to show latest information, advice, etc.  Please also monitor the Project Intranet, recently introduced.  You are welcome to access either of these from college or wherever is convenient. 

You can monitor these pages while logged in on the Teaching System as a Mentor user.  However, it appears that Netscape (when run on the Teaching System) sometimes interacts adversely with some graphical displays, giving (for example) purple text on a black background.  

To circumvent this, note that the PCs are equipped with Firefox and Internet Explorer browsers which you can run locally (on the PC rather than on the Teaching System).  This eliminates the problem.

Shared Mentor Workspaces

This project makes use of shared workspaces, shared between members of the groups of 2 formed at the start of the first session.  Although you will login using your own identifier, all your project design materials will be held in the shared workspace.

Users often receive an email from the Computer Operators (text in italics below) to explain some of the features of shared workspaces. The recommendations in the email provide some useful refinements, but are not strictly essential for our use on the Mentor project.  In case this message is not automatically sent this year, the gist is presented below.

A shared group directory has been set up for you called mentorX (where X is a number 2-9). In order to access this shared filespace you may wish to create a link between your own file space and the shared directory. On the Unix Teaching System in the DPO type:

ln -s /usersG/ptiivlsi/mentorX ~/mentorX      where X is your group no.

The instructions in the Project Guide tell you how to change directory at the start of every session using:- 

cd /usersG/ptiivlsi/mentorX 

If you follow the advice above with the ln command, this simplifies to typing (while in your home directory): 

cd mentorX

It is important that the files created in the shared space have the correct permissions, and this involves using the umask command. Before changing directory (command cd) on the Unix Teaching System into the shared space type: umask 007 so that any files created or edited in your group are readable and writable by everyone in the group. ...... The umask command needs to be typed EVERY time you login to the Unix Teaching System and wish to share files in this group.

For this project problems will arise if you create files that are editable only by the person who created it: all data needs to be shared between both members of each pair.  The mentor_start_env script which we recommend you to use contains the recommended umask command.  Its effect persists throughout the Mentor session, but the setting is restored to the normal value on exit.  Please note the following:

When you finish your Group session, log out. This will have the effect of resetting the default umask for the files in your own filespace. If you have any problems get help from the Operators whose office is at the far end of the DPO by the printers.

Logging in

As per the printed notes.  Log in to Windows XP by first hitting <Ctrl><Alt><Del>, then entering your own UID and password. 
Start up the browser pointing to this page(!) or the Project Intranet.

Click the Mentor icon, which actually just starts the X-win32 application so you can login to the Teaching System.
Login, using your normal UID and password.
You will be presented with a choice of servers on login. Normally you should choose the one allocated to you, then give commands as advised in the notes:-

. mentor_start_env   (NB the dot-space at the beginning of the line)

Pause while the window manager fvwm etc starts up


Note the availablity of a popup menu (click over fvwm desktop with RH mouse button) which lets you run a couple of useful Mentor utilities.

Logging out

Once you have closed all Mentor application windows (Design Manager last of all) and the associated transcript windows, left click on the fvwm desktop and give the command: Exit fvwm > Yes, really quit.  This should clear the desktop and invoke the server menu.

Next, exit from the Xwin32 utility by clicking on its wpe1.jpg (790 bytes) button at top right.

Finally, log out of Windows XP by clicking wpe2.jpg (1230 bytes) and selecting the option: Shut down ..    followed by   Logon as different user.

See below for slight variations on this if you login from other workstations (i.e. outside the scheduled project times).

Remote logins (from other tw- workstations) 

The following procedure, which assumes you propose to login to your account via workstation tw212 in the DPO:-

Login in the normal way to tw212 as yourself.  An xterm window should appear.  Don't start a Window Manager at this stage.

In the xterm window give the command

xon tw3


xon tw6

(according to the server required)

You may be required to give your password at this stage.

Now give the commands:

. mentor_start_env (note the 'dot-space' at the start of the line.   This is important!)
mentor (you may need to use a different script if your terminal has an unusual keyboard configuration, e.g HP

Then continue to work as normal, ignoring the first (login) window until you actually want to logout.

Queries by email

If you have any queries about the project, you can email them to:-

Using this address ensures that the message will be copied to all demonstrators.

Experiment on Electrical Testing of the Ring Oscillator

Important: please make an early start on this experiment.
There is not enough equipment for everyone to do the experiment at the same time.

The experiment relating to Electrical Testing of the Ring Oscillator will be set up in the E & I E Teaching Lab and will be available from Friday 19th May.  The Lab Guide for this in included at the end of your Project Manual, but there will also be a few copies in the E & I E T L.  A demonstrator will be available for this part of the project during scheduled sessions (only), when there will be a sign-up sheet, but it may not be possible for the demonstrators to be present in the E & I E T L full time.  You can carry out the experiment, with your partner, at any convenient time (during laboratory hours) from Friday 19th onwards, and you should include the material in your Final Report

First Interim Report

The deadline for the first interim report for the project is on Monday 22nd May.  A summary information about the expected content of the report is given below. 

Note that this is just the bare bones; a good report will also give attention to overviews and aims of work carried out as well as conclusions drawn and any implications for future work. The report should be 2 written sides maximum, plus appendices which may include calculations, printed schematics, listings etc.

Handing in your report

You may start Lab Guides 4 and 5 as soon as you feel you have completed Lab Guides 1, 2 and 3 and gathered the necessary material for the first report. 

Second Interim Report

The deadline for the Second Interim Report for the project is Monday 29th May. The report should be 2 sides maximum, plus any printed schematics, listings etc.

Basically, this report should cover the material gathered in labs 4 and 5.  These are the main points:-

Note that this is just the bare bones; a good report will also contain:-

Please note also the following:-

Handing in your report

Final Report 

The deadline for the Final Interim Report for the project is Saturday 10th June 5 pm. The report should be 10 sides maximum, plus any appendices (printed schematics, listings etc).

A good report is likely to contain references to most if not all of the following.   Please note that the list is not intended to be definitive, and there is no significance to the order in which the items are listed. 

Be sure to see also the Third Year Project Guide

Please note also the following:-

Handing in your report

Hints and tips 

Modelling the sequence generator in HDL

You will need to determine how to create a shift register of 6 elements or greater, then consider how to connect the appropriate shift register outputs to the inputs of the XNOR gate.   We would like the maximum length sequence available from a 6 bit register.

You can read about possible configurations for the shift register in The Art of Electronics by Horowitz & Hill, C.U.P., p. 656-7 in the 2nd Edition. 

For a shift register of m bits with feedback taken from outputs n and m, the maximum length sequence available is given in the table below, which is based on the data in H & H.

m n Length
5 3 31
6 5 63
7 6 127
9 5 511
10 7 1023 etc

Want to find out more about VHDL?  Check out this URL, where you can access an on-line course covering the basics (caution, this involves a largish download) ...

Printing out HDL listings using Design Architect

The use of mgcplot is also described in Lab Guides 2, 3 and elsewhere.

Problems visualising the structure of the MOS transistor?

If you are experiencing difficulty in appreciating how the layout diagrams map onto the 3D structure of the MOSFET, you may like to try out our new Java-based visualisation tool.   This offers a 3D view of a MOSFET showing its structure, and uses the same colour codes as used in (most) layout packages.  You can also see descriptions of layer names and SEM images of real device features for comparison.

This work is the result of a 4th year M Eng project carried out by Amr Monawir, who now works at Xilinx.  To access it, click the icon below; the Java applet should open in a new window:-

Go To button
3D Model of a MOS transistor

Other applets for MOS transistors

Design a fast gate!

For the layout/verification section, Labs 7 and 8, remember we are seeking to try and make as fast a NOR2 gate as we reasonably can.  You should do what you can in the layout to keep parasitic capacitances to substrate as low as possible.

Can't find models for TR_N/TR_P

In Lab 7, be sure to follow the instructions for creating a viewpoint for Accusim with some care.  In connection with this, we have on fairly rare occasions encountered a problem in which Accusim gives the error message:- 'Can't find models for TR_N/TR_P'.  You may not meet this problem, but if you do, ask a demonstrator or contact us by email (mentor1) without delay.

Strange colours afflict ICgraph display after using Netscape Navigator or after print preview

It appears that Netscape (when run on the Teaching System) sometimes interacts adversely with some graphical displays, giving (for example) purple text on a black background.   Until we can ascertain if there is a fix for this, you may wish to avoid using Netscape on the Teaching System when logged in as mentorxx - use the local browser on the PC instead.  Otherwise, use Netscape to check the page, then close it down before starting up Mentor.   You can always re-open it later, for example, by using the popup menu option on the RH mouse button (click RH mouse button with cursor over fvwm desktop).

In Lab 8, we have occasionally noticed an adverse interaction between ICgraph and ghostview, the graphical viewer used to preview and print layout plots.  This manifests itself as follows:-

This problem does not appear consistently, and it is possible it occurs only at the first use of ghostview.

We have no complete solution to this, other than to exit and restart your ICgraph session.  We recommend you leave preview/printing until your design work is complete and the design saved.

No printable files visible in mgcplot

In Mentor applications run on the Teaching System, printing or plotting involves two stages.  Typically, you use the Print feature in Design Architect, ICgraph, QuickSim II, Accusim or one of the other Mentor applications, and specify the printer device as mgcps_a4.   This prepares the output for a monochrome Postscript A4 printer but does not actually send the output to a printer.  The mgcplot utility is provided to control the final printing operation.  When you run mgcplot, you should see something like the following:-

tw400% mgcplot
Processing files in /export/mgcC4/tmp for group mentor1.
Do you want to process A4 colour postscript output [N]?  N
Do you want to process A4 HPGL2 output (no preview available) [N]?  N
Do you want to process A3 postscript output [N]?  N
These are the mentor files that you have created.
1) va211.sheet1.1
2) quit
Choose a file or quit

Note that your UID will appear in the file name in place of va211.   The keyword sheet1 normally refers to a sheet created by Design Architect.  The final 1 gives a serial number to distinguish this file from other prints you may have created.

The symptoms of the problem are that on executing mgcplot no files are seen, for example:-

These are the mentor files that you have created.
1) quit
Choose a file or quit

Possible causes:-

Colour plots appear as black and white only

The symptoms are that under Preview using Ghostview the plot is entirely black & white.

Check that you chose a printer that supports colour in MGC > Setup Printer. The standard choice is mgcpsa4_colour.

Colour plots appear as black and white with occasional parts in colour

There is an adverse interaction between XWin-32 and ICgraph which under certain circumstances interferes with generation of colour postscript output.

The symptoms are that under Preview using Ghostview the plot is largely in black & white.  Occasional parts may be in colour (often red polysilicon).

To fix this you must ensure that your XWin-32 session is set to pseudocolor support.  Left click the System button (at extreme left of XWin-32 title bar); select Xutil-32 and then choose the Colours Option.   Each mouse click on this option toggles its state between On and Off.  Make sure this option is checked.  In Hummingbird eXceed, use System > Tools > Configuration and choose Video.  Check that Server Visual is set to Pseudocolor.  If you change this parameter a restart of eXceed may be necessary.

Creating a hierarchical layout for your design (Lab Guide 8)

In 2005 the following is no longer relevant, since we are this year using a more recent version of Mentor, ICFlow 2003.3.

We have become aware of some unusual features of Mentor C.4 (the version in use with the VLSI project) that particularly affect those parts of Lab 8 concerning the hierarchical layout.  Producing a flattened layout is not affected. The symptoms are as follows:-

These effects are specific to C.4.  More recent versions do not exhibit these problems.  The causes of the problems mentioned and the workarounds we have introduced are summarised below.

Accessing Mentor from outside CUED

A number of users are taking advantage of college computers or possibly personal machines to access Mentor outside the scheduled sessions.  We will give what help we can with this, but it is a non-trivial exercise, and there is a risk you will spend more time tweaking software than designing your chip!

Here is a recipe that has been found to work with Hummingbird Vista eXceed Version 6.0 ...

Transport = tcp
Server =
Port = 7100
Status = Load


Page created by David Holburn   Monday, 15 May 2006