Opus manual

Simplified OPUS Users' Manual

This is not a real user's manual. In the introduction some background information is given on the tool itself and on the design procedure. In the second part several topics are described as an extension of the Primer section. (They may be regarded as FAQ's.) This is followed by guidelines and hints for designers of standard cells -- mainly for our students.

Introduction

Cells and Views

In OPUS the construction unit is cell. A cell does not necessarily constitute a complete logical or circuit function. It is just a set of several (or even only one) circuit elements which are on whatever basis kept together. In different phases of circuit and layout design different kinds of data are required and processed. For instance geometrical (picture) information for a circuit diagram, electrical information for a netlist (parts and their connections), and another set of geometrical data for the layout of the very same cell. These data are collected and stored in the different views of the cell, such as:

Schematic: circuit diagram (what it looks like).

HspiceD, EldoD: contain Spice information for the element.

Layout: silicon structure (geometrical).

Extracted: netlist generated by analyzing the structure of the layout.

Abstract: contains an abstract representation of the layout for use by Cadence place & route software.

Behavioral: the Verilog description of the cell.

For using cells as hierarchic elements they have the view:

Symbol: "black box" representation of the cell for usage in higher levels of the circuit hierarchy.

Parametric Cells

Cells may have numeric or textual parameters. Filling in these parameters when instancing the cell may result in different shapes, size, etc. A typical case for parametric cells are the transistors used in OPUS Primer.

Cell Hierarchy

Cells are building blocks. They can be used as parts of other cells. It is always an instance of the cell, represented by a black-box symbol, with a unique instance name which is placed into the higher level cell. Neither the number of instances nor the depth of the hierarchy is limited.

File System

When starting, OPUS asks for a Home Directory which is not necessarily identical with your user's home directory. OPUS will do all its jobs in this directory, mostly in subdirectories of this one. There are only a few exceptions such as the logfile CDS.log. They are placed into the user's home directory. The most important subdirectory in OPUS' home directory is the Working Library.

A cell as such does not exist. It only exists in its views. Accordingly, in the working library, where all the cells with their data are stored, each cell is represented by a subdirectory having the name of the cell. The subdirectory contains the views of the cell which, again, are subdirectories containing several data files of the view concerned.

The great majority of the files are binary. They cannot be read or processed by text editor. Their existence may be checked on the Linux level but they must not be moved, copied, deleted or operated on by the operating system. All these tasks are organized and performed by the Library Manager of OPUS.

Selected Topics

The Primer provides all necessary information for the very first steps with OPUS. However, after having started a real design, you will be confronted with new problems and questions. The selected topics which follow are intended to help going on.

General

Windows of OPUS

The windows of OPUS have similarities in appearance and functionality to those in MS-Windows (Fig. 35.). They all have a title bar at the top having the usual 3 buttons for iconifying, making full screen and closing. Dialog boxes only have the closing button. The closing buttons (X) often do not react, in such a case some other button has to be used. OPUS just like Windows usually has a menu bar with drop-down menus.



Fig. 35 Typical OPUS window

Functionality of some general purpose buttons:

OK Do it and close the window

Apply Do it and do not close the window

Cancel Do not do anything, close the window

Close The same as cancel

Hide The settings are valid and the window is iconified

Help The help system is called

You may execute commands in different ways resulting in the same action. In case of a complete window like that of Fig. 6 (page 5) you may use the roll-down menu at the top of the window, the buttons with icons on the left, or hot keys like the ones in the OPUS Primer, referred to as .

Specifying the Default Home Directory for OPUS

When coming up after start, the first activity of OPUS is a prompt for the home directory for the design activities. You may already have made myopus for this purpose (mkdir myopus). If you insert a line into your .bashrc file:

setenv AMS37_DESIGN_DIR myopus

then OPUS will offer myopus as its default home directory, so depressing only is enough (instead of typing myopus).

Attaching a New Library

If there is a library in the computer system where you can find and fetch cells for your design work then this library has to be attached to your OPUS environment. The name of the library is just the name of the directory where it is stored, and it has an absolute path in the system. These two pieces of information have to be given to OPUS. You can do that in the Library Manager of OPUS. Left click Library Manager:Edit->Library Path. The Library Path Editor window opens with columns for entering the name and the path. Then left click Library Path Editor:File->Save. This way, if necessary, you can also modify or delete libraries. Exceptionally, this is a job which may be done on LINUX level, too, by editing the file cds.lib in the home directory of OPUS.

The ESCAPE function

If an editing function is activated then it remains active until another one will be switched on. If, instead, on any reason, no active function is needed then depress and the system returns to an idle (waiting) state.

Selecting objects

1. 
   Move the cursor to the edge of the object or place it over it. The contour of the object changes its color and forms a dashed yellow line. (Sometime the dashed yellow line just appears because in "normal" state it is not displayed such as the selection box of an instance, see Fig. 36.) With a left click it turns to a solid white line that indicates the selected state. In case of uncertainty about what has been selected depress . A property sheet appears showing among others the name of the object, too.
   

Fig. 36 Selecting a transistor instance

2. 
   Making a left drag a yellow rectangle can be drawn on the screen. All items being completely inside of the yellow rectangle will be selected by this method.
   

Entering Parameter Values

Parameter values consist of three parts: a number, a scaling factor (such as m for milli or u for micro) and a unit. The scaling factor must immediately follow the number, while the unit (always a full unit as V or Ohm and never mV or kOhm) must be separated by a space. For example: 13.5k Ohm. In most cases OPUS adds the unit automatically if you do not type it.

Property sheets

Cells consist of objects, be it a piece of wire, a rectangle, a transistor or an instance of another cell. They can be selected by mouseclick. When depressing the Edit Object Properties window pops up (property sheet of the object, see Fig 37.) showing the properties (parameters) of the selected object and offering the possibility to change them.



Fig. 37 Property sheet of a label (wire name)

For instance, the size of a rectangle, the location or the name of an instance can be changed. Changing the name of an instance means replacing it by another one. The change will be performed only after OK or Apply is clicked at. After Apply another change may be made but, more important, if in this situation another object will be selected, then the property sheet automatically brings up the properties of the newly selected object.

Setting Parameters of Operations

When creating new objects or modifying them with editing operations you may change properties and parameters of the selected operation by depressing the special key . A small window opens offering possible changes. The possibilities depend on the operation selected. For example, you may set the width of a wire in a schematic or of a path in a layout. Different Snap Modes control the direction of a path or the direction of the movement when performing a Move. (Fig. 38.)



Fig. 38 Property sheet of the operation move

Searching

A favorable aid in editing layout as well as schematic is the function Search or Search and Replace. From the main menu it can be invoked by clicking at Edit->Search->Find… (Relplace…). A dialog box opens with many different buttons and edit fields for specifying the search (Fig.39). The object matching the criteria will be selected. Using wild characters such as * multiple search can be done. If an object is selected it can either be edited by hand or else some property can be changed by means of the Replace function.



Fig. 39 Search dialog box