Multi-Dimension Visual Analysis

This invention generally relates to improvements in design analysis of logic and circuit simulators and more particularly to a technique that employs multi-dimensional visualization techniques to analyze and display large volumes of data more effectively.

High speed logic and circuit simulators are used throughout the computer industry to aid in the design of complex systems. High performance simulators generate enormous amounts of data making storage of the information impractical. In order to pinpoint problems effectively, the information must be displayed to the designer as it is generated. However, current technology only allows the information to be presented in the form of waveforms, tables or compared to known values to detect problems. A prior art technique for analyzing information on a computer channel is disclosed in U.S. Pat. No. 4,773,003. This patent detects a pre-selected signal line event and displays the information on a two-dimensional display for further manual analysis.

VLSI designers have difficulty trying to debug designs when a large amount of information is displayed without trend or summary information. For example, it is very difficult for a designer to analyze the effect of power reset on all macros. The source of a problem is often very difficult to trace to its cause. A typical network predecessor tree for the problem just described can be very large and quite deep. The tree also grows quickly to obscure the source of the problem further.

State of the art waveform displays help the designer in the analysis of networks. However, they only focus on one aspect of the problem at a time and have no capability for correlating multiple functions to decipher the common source of the problem.

Waveform programs are offered by many of the Engineering Design Association (EDA) vendors such as the LSIM simulator, ZYCAD, IKOS and Mentor. A standard approach plots the information on two-dimensional waveforms for each net as a function of time. The plots are displayed on a graphics device for further manual interrogation. As many as fifty nets are plotted in the vertical direction while time is plotted from an origin of zero at the extreme left-hand side. FIG. 1 shows an example of a prior art net display. To debug many networks and visualize the simulation information globally, a new approach is necessary.

The invention consists of a computer and graphics display for processing large amounts of information and displaying that information graphically. Software processing of the information and graphic display of the processed information focuses attention to suspect areas employing colors and shading techniques to quickly call the user's attention to problem areas.

The foregoing and other objects, aspects and advantages of the invention will be better understood from the following detailed description of the preferred embodiment of the invention with reference to the accompanying drawings, in which:

FIG. 1 shows a prior art example of a waveform display of nets;

FIG. 2a is an illustration of a many net display in accordance with the invention;

FIG. 2b is a blowup of a waveform display of one network of a many net display in accordance with the invention;

FIG. 3 is a flowchart showing the logic for implementing a many net display in accordance with the present invention;

FIG. 4a depicts an all nets displays in accordance with the present invention;

FIG. 4b depicts an all nets displays at Time (T) in accordance with the present invention;

FIG. 4c depicts an all nets displays at Time (T) in accordance with the present invention;

FIG. 5 illustrates a three-dimensional depiction of an all nets display in accordance with the present invention;

FIG. 6 is a flowchart showing the logic for implementing an all nets display in accordance with the present invention;

FIG. 7a is a circuit diagram of the physical design of a semiconductor;

FIG. 7b is an all nets display of the semiconductor depicted in FIG. 7a in accordance with the present invention;

FIG. 8 is an all nets display of clock with space relationship in accordance with the present invention;

FIG. 9 is an all nets display of two features in accordance with the present invention;

FIG. 10 is an all nets display of two features with a different selection of time space compression in accordance with the present invention;

FIG. 11 is an all nets for all time changing in real time with color density and x, y relationship in accordance with the subject invention; and

FIG. 12 is a block diagram of the hardware in accordance with the subject invention.

Starting with the simple two-dimensional multiple net display as shown in FIG. 1, a simple initial step entails the compression of the vertical plots until all plots are compressed. Thus, the transition from the lowest state to the highest state would be shown as a line color change not a vertical deflection of a polygon waveform. As more and more net states are plotted on one screen, the limiting factor is the number of scan lines on the display. The limit is reached when the logic states are represented by a single pel or line of pels and encoded using color as a differentiating factor.

The waveform of the clock net in FIG. 1, net 10, required one-hundred pixels to show the logic state transition. Employing the technique just described, the rise and fall transition of network 20 in FIG. 1 is represented in FIG. 2 by color differences on one horizontal scan line. Two green pixels are indicative of the down state, then four red pixels for the undefined state and four blue pixels for the up state. The green pixels are represented in FIG. 2 by white square areas, while the red pixels are represented by lighter shades of grey, and the blue pixels are represented by black areas in FIG. 2.

In FIG. 2 time is plotted on the X-axis while each line of the Y-axis is a separate net. So, for example, at 30 a transition from logical high to undefined is indicated by the black area changing to grey. In FIG. 2, each net occupies a single scan line. Thus, a group of undefined nets would be visible as a red area 40 on the display.

The resulting display has patches of color that change from left to right as the simulation proceeds in time. By allowing the user to select the vertical order of the net display, for example net predecessor, net successor, or distance from input or output port, various images are created to enhance the visualization process.

Referring to FIG. 2, an output net appears near the bottom 20. The output nets 20 is undefined at time zero 25, but become defined by time four 27. The net represents a typical power reset problem of a microcomputer or a fetch to an invalid address. A user notes that the net becomes undefined at time five 30, but the cause is not apparent based on the display in FIG. 1. Using techniques of the prior art, such as the waveforms illustrated in FIG. 1, the user would have to select the specific output net, and then begin his trace backwards through multiple windows and networks. In FIG. 2, the capacity to visualize many more networks enables a comprehensive view of a plurality of networks and the ability to pinpoint the source of an error quickly and accurately.

Many line drawing routines are presently available for implementing the line drawing calls of the invention. Packages such as the Graphics Programmer's Hierarchical Interactive Graphic System (Graphics) or the IBM 3277 Graphics Attachment PRQ described in IBM publication SH20-2137 provide the type of graphics support necessary to implement the invention. The graphic packages are designed to execute on a variety of standard processors and displays such as IBM's PC/RT with corresponding high resolution graphic's display or the IBM 5085 controller attached to a System/370 Host to drive an IBM 5080 display as shown in FIG. 12.

The logic for implementing the invention is displayed in FIG. 3. In function block 100, the mapping of the network is determined. Information pertaining to the color or intensity of each electrical state and the maximum number of nets to display in the raster image is predefined by the user in conjunction with function block 110. Then, the net locations are allocated by logical or physical nearest neighbors in function block 120. The user must then select the subset of nets that can be displayed on the display in function block 130.

The time window of interest is selected next in function block 140. Then the number of time steps is calculated in function block 150, and the delta movement in the horizontal direction for each step is calculated in function block 160.

A loop is used to process each net data simulation as time elapses commencing at function block 170 where the display is reset for the particular horizontal (x) coordinate. Function block 180 resets the subnet data pointer to the start of the left side of the display and function block 190 increments the display to the next vertical (y) location for displaying the next net's state. The net is incremented in function block 200 to get the next net simulation information.

Then an inner loop is entered at function block 210 for processing the net transition information. Function block 210 increments through the transition information until the net is completed as tested in decision block 250. A test for a transition in the net data is performed at decision block 220 and the information is plotted at 240 if a transition is detected in decision block 230.

Following the plot step at function block 240, or a detection of no transition at decision block 230, control returns to decision block 250 to determine if the net processing is complete. If it is not, then control returns to the inner loop at function block 210 to continue to process net information. If it is complete, then control returns to function block 170 to increment to the next net. Processing continues until the information is halted or the process is interrupted.

The many nets display allows a designer to look at large chip macros that get a summary of its behavior by looking at one graphic image. Although, the many nets display just described is helpful, most system designs exceed one-thousand nets. Thus, a user would have to page through tens or hundreds of many net displays to attempt to get the overall view or find exception conditions. This is impractical.

To see the global view of the system, the nets must be represented by a three-dimensional volume in space and time on the graphic display. The three-dimensional volume draws the net as a line in three-dimensional space with color changes for state transitions.

In some of the following figures the line that represents a net's state is drawn as a large cylinder with a radius that is a function of how many nets one would like to display at one time just like in the many net display where the lines have a width which is a function of the number of nets to be displayed. An example is FIG. 4a which depicts the all nets display for the preceding example. The display can be panned by net face of the cube to a time T 400. Notice that at time (T) the last net that commenced in an undefined state reaches a defined state at the tip 420 of the cone 430.

The face or plane at time T is called all nets at a time T in the cube of all nets for all time as shown in FIG. 4b at label 450. Then, instead of drawing the full cube, the view from the right face can be drawn as the state of all nets at time T as shown in FIG. 4c. The size of all nets up to time (T) can be expanded to fill the graphic display, where the cube outline is kept in all figures to get visual reference 401.

The plane for all nets at time (T) provides a starting point to perform further analysis using conventional tools such as waveform display to analyze the specific subset of information. The key differentiating feature is that this technique provides the user with a display of the entire system. Based on the system display, the user can hone in on a problem area and quickly isolate the problem.

Now one can attempt to show how a user might visualize the series of all nets at overlayed incrementing times and result in a visual impression as shown in FIG. 11. For example, assume that the designer would like to explore the active or high power states and that one net starts the chain reaction as depicted by the tip of cone 460 in FIG. 4.

Looking at the successors of that net we can imagine the cone of successors 470 could all change to a high power state. Looking at the all nets display at any one time like T as shown in FIG. 4c, a circle 460 is displayed as a slice of 470.

If we flash each all nets at time t(n), as n increases in time, one after another or average them all together, the viewer visualization of the images would average the nets together where the center 460 would appear red 1110, but the outside rim would only appear red for a single time step 1120. Thus, the resulting image would have less color in the outer area due to a display of one-tenth duration. Further, the red color would increase in brightness as attention was focused on the center 1110. The hottest area of the circuit would convey clearly via the red area. The solid circles 1130 and 1140 represent nets that never change states.

For implementing the all net all time display, three-dimensional mapping software is used such as the support provided under Mathematica, which is described in "Mathematic, A System For Doing Mathematics By Computer", Stephen Wolfram, 1988, ISBN 0-201019334-5.

The logic for the all nets display is very similar to the logic used for the many net display. Lines are drawn in three-dimensional space instead of two-dimensional space, and the user selects a point of view to facilitate the correct perspective. One key to this process is selecting the proper color or non-color to facilitate views through the three-dimensional object. For example, if one is interested in the undefined or nets that never transition then they should be the only nets plotted to avoid cluttering the object. It may also be useful to pass transition data to a three dimensional surface shading routine and/or plot the 3D object as a stereographic image to help in the visualization process.

FIG. 5 displays only undefined states of nets and unchanging states of all nets. The nets that are undefined are represented by the cones labeled 300, 333 and 340. As time increases from left to right, the nets that were undefined become defined at the tip of the cone labeled 301. The cylinders 310 and 320 represent nets that never changed state, and the cones that increase in size from left to right 330 and 340 represent nets that are going undefined as time increases.

The invention can also identify power hot spots, lack of net activity, and circuit noise for a physical chip layout. All nets at time T graphically depict the function of interest, in this case power hot spots, over each of the networks of interest. The key to this analysis is creating a mapping of the physical chip to all nets space mapping that allows the designer to readily comprehend trouble spots on the chip.

For the analysis of net activity no more preprocessing is required, for net power or current the color mapping may be different. For example a 0 logic state might be a higher power state than a 1 logical state and thus select the color red for that specific circuit in the 0 state.

For delta current switching analysis the net transition times could be highlighted with color changes. Results can be displayed by commencing at time 0 and displaying each plane at increasing time steps. The rate of display changes is also adjustable to average the colors and get a global sense of the state of the machine. For example, if nets in a specific area are usually in the high power state, then the integrated color of that area might be red. The net states could be averaged automatically, or as the nets are drawn on the screen, but it is much better to allow a user to watch the display for exceptions and process the visual information dynamically.

The detailed logic associated with all nets processing is shown in FIG. 6. The logic is identical to the many nets display except for the additional loop for filling the three-dimensional area in function blocks 430 and 440. The nets are pre-ordered in function block 320 so that the (x,y) starting point of the net is a linear function of the primary driver circuit location (cx, cy) on the chip or board design. The initialization step also requires the user to select a perspective for viewing the three-dimensional display and decide if a static display is more effective or repetitive viewing of all nets at time t(n) as n increased in time.

If the later is required, then the time (t) function is representative of a small subset of time to display all nets at time t. Further, the X,Y,t starting point could be reset to zero to overlay all nets displays instead of spreading them out in 3D space. This facilitates dynamic processing of the net state averaging.

For an electrical circuit example, the all net display would perform the following steps.

1) Select the color, or intensity to represent each electrical state.

2) Select the states that require transparency.

3) Select the user viewport (X, Y, z) in three-dimensional space.

4) Decide on a maximum number of nets to display.

5) Allocate the nets by physical position and assign X, Y, 0 starting points.

6) Create a set of physical points if required.

7) Select a subset of points that will fit on the display.

8) Determine the time window of interest.

9) Decide on the time vs. spacial raster rate.

10) Calculate the number of time steps and delta T per time step

11) Do for each net data display result:

a. Index to the next X, Y, 0 start point representing nets' starting point

b. Reset net state offset counter or transition pointer

c. Do for net transitions

1) Increment net pointer to obtain next set of net simulation data

2) Test for a transition in the net data and change color

3) Plot the line segment value form the last transition in three-dimensional space

4) Plot the volume if time compression or decompression in three-dimensional space

5) Exit loop if data or time window limit is attained

d. Enddo (net transition)

12. Enddo (net data)

A possible alternative enhancing the visualization uses a technique for displaying a set of line segments for each net. The display would consist of a polygon area that represents the net state at time T and the shape would represent all the physical points in a specific net on a chip, card or board. Then, a further enhancement provides time compression so that the all net at time T plane becomes all nets at times t(n) through t(m).

For example, let the shape of the area be a square. Further, let the square represent sixteen time steps, whereby time is rastered across the square displaying the sixteen time steps and forms a pattern of colors representing the time window. The resultant display of the chip simulation states correlates the E-beam voltage contrast image of the physical chip in operation with the refresh rate of the raster display.

FIG. 7a shows a volume marked off by a boundary 700 containing a sub volume labeled 702. The physical chip design is shown in FIG. 7b labeled 710. The mapping from the x, y location of net drivers on the physical chip is indicated by 720, 721 and 722. It is clear that the nets located in the macro 701 are the only nets on the chip that commence in the undefined state 730 and become defined at some later time 740.

Given the x,y,z location of that point in the graphic net space volume 700 one can locate the xl 741, yl 742 point on the chip and thus the net that was the last net to get reset to a defined state. Further, the event clearly transpired at time 743.

The three shaded FIGS. 8, 9, and 10 show the net state lines as cylinders to emphasize the net and make it clearly differentiable. The single net shown is a clock waveform and this time the net is defined and oscillates for all time.

FIG. 8 shows an area marked off by a boundary 800 which is all net space. The volume contains a sub volume indicated by 802 representing a single net. The net is represented by sixteen cylinders with alternating white and black as the net changes its logical state in time. The shape selected matches the shape of a net on a chip (S shape). Time range from t0 to t8 in increments of one second. At time t8, the net is in the logic 0 state and is shown as all white.

Since the shape of the net display represents the shape of the physical design the user can see the entire physical expanse and logical state of the network. FIGS. 9 and 10 highlight another feature. The shape selected matches the shape of a net on a chip (square), and the clock rate of the net matches the selection of the depiction of time. By allowing user control of this compression or decompression of time into space display, the user can investigate patterns which helps the user to understand the way the system is functioning. In FIG. 9 instead of having the planes represent one time period as in FIG. 8 time can be compressed or envisioned as rastered across the image.

Again a volume marked off by a boundary 900 for all nets contains a sub volume indicated by 902 representative of a single net represented with sixteen pels. The raster of time is shown with the time label 903. The last time point is 910. A different selection of time space compression is used to generate FIG. 10. Notice how different it looks, and the different patterns from the side 1010 and end view 1020.

An embodiment of the invention developed by the inventor to analyze and debug VLSI chips is provided below to clarify the detailed logic of the present invention. The logic is presented via a Pascal source code listing currently employed by IBM. ##SPC1##

While the invention has been described in terms of a preferred embodiment in a specific system environment, those skilled in the art recognize that the invention can be practiced, with modification, in other and different operating systems within the spirit and scope of the appended claims.