ASIC Implementation Design Cycle

HDL Implementation Design Cycle

Following diagram shows the basic flow of the complete HDL Implementation design cycle.

Netgen - The Circuit Netlist Comparison (LVS) and Netlist Conversion Tool

Netgen is a tool for comparing netlists, a process known as LVS, which stands for "Layout vs. Schematic". This is an important step in the integrated circuit design flow, ensuring that the geometry that has been laid out matches the expected circuit. Very small circuits can bypass this step by confirming circuit operation through extraction and simulation. Very large digital circuits are usually generated by tools from high-level descriptions, using compilers that ensure the correct layout geometry. The greatest need for LVS is in large analog or mixed-signal circuits that cannot be simulated in reasonable time. Even for small circuits, LVS can be done much faster than simulation, and provides feedback that makes it easier to find an error than does a simulation.

Netgen version 1.3 is the stable branch and has been essentially unchanged for several years. The development branch version 1.4 is an attempt to bring netgen up to par with the industry-standard Calibre tool from Mentor Graphics. Since (as far as I know) all LVS tools are based on the same class partitioning algorithm, this effort is not as difficult as it may seem. Mostly, netgen must be made to properly understand hierarchy, device properties, and generate a more readable output. All these changes are now underway (as of November 2007, when the development version 1.4 branch was created).

Netgen was developed independently of magic, written by Massimo Sivilotti, and eventually incorporated into the beginnings of the Tanner L-Edit suite of tools. However, the original code was left open source, and so I have incorporated it into the Tcl-based suite of tools including magic, IRSIM, and xcircuit.

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IRSIM - tThe Switch-level Digital Circuit Simulator.

IRSIM is a tool for simulating digital circuits. It is a "switch-level" simulator; that is, it treats transistors as ideal switches. Extracted capacitance and lumped resistance values are used to make the switch a little bit more realistic than the ideal, using the RC time constants to predict the relative timing of events.

IRSIM shares a history with magic, although it is an independent program. Magic was designed to produce, and IRSIM to read, the ".sim" file format, which is largely unused outside of these two programs. IRSIM was developed at Stanford, while Magic was developed at Berkeley. Parts of Magic were developed especially for use with IRSIM, allowing IRSIM to run a simulation in the "background" (i.e., a forked process communicating through a pipe), while displaying information about the values of signals directly on the VLSI layout.

For "quick" simulations of digital circuits, IRSIM is still quite useful for confirming basic operation of digital circuit layouts. The addition of scheduling commands ("at", "every", "when", and "whenever") put IRSIM into the same class as Verilog simulators. It is, in my opinion, much easier to write complicated testbench simulations using Tcl and IRSIM. I have used IRSIM to validate the digital parts of several production chips at MultiGiG, including the simulation of analog behavior such as PLL locking.

IRSIM version 9.5 was a long-standing and stable version that corresponded to the relatively stable Magic version 6.5. When magic was recast in a Tcl/Tk interpreter framework (versions 7.2 and 7.3), IRSIM could no longer operate as a background process. However, it was clear that if IRSIM could also be recast in the same Tcl/Tk interpreter framework, the level of interaction between it and Magic would be greatly increased.

I set about to create the "new" IRSIM, although it came along in fits and starts as I had time to work on it. Because the original "analyzer" graphic display window (and GUI, to a very limited extent) was written in Xt (the rather primitive window system that is an integral part of X11), it was scrapped for a while. In its place, I substituted graphs in "Blt" based on the same in "tclspice" (see SourceForge for the tclspice project). Unfortunately, "Blt" insists that all data vectors must be real-valued, which is 1) a severe waste of space for binary digital values, and 2) is unable to represent the concept of an "unknown" value that is so crucial to fast switch simulation. So, eventually I was forced to scrap BLT and actually sit down and code out a real Tcl-based analyzer window and GUI. The result is finally done in revision 9.7.3.

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XCircuit - The Circuit Drawing and Schematic Capture Tool

There are drawing programs, and there are schematic capture programs. All schematic capture programs will produce output for inclusion in publications. However, these programs have different goals, and it shows. Rarely is the output of a schematic capture program really suitable for publication; often it is not even readable, or cannot be scaled. Engineers who really want to have a useful schematic drawing of a circuit usually redraw the circuit in a general drawing program, which can be both tedious and prone to introducing new errors.

XCircuit is a UNIX/X11 (and Windows, if you have an X-Server running, or Windows API, if not) program for drawing publishable-quality electrical circuit schematic diagrams and related figures, and produce circuit netlists through schematic capture. XCircuit regards circuits as inherently hierarchical, and writes both hierarchical PostScript output and hierarchical SPICE netlists. Circuit components are saved in and retrieved from libraries which are fully editable. XCircuit does not separate artistic expression from circuit drawing; it maintains flexiblity in style without compromising the power of schematic capture.

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Magic - The VLSI Layout Editor, Extraction, and DRC Tool.

Magic is a venerable VLSI layout tool, written in the 1980's at Berkeley by John Ousterhout, now famous primarily for writing the scripting interpreter language Tcl. Due largely in part to its liberal Berkeley open-source license, magic has remained popular with universities and small companies. The open-source license has allowed VLSI engineers with a bent toward programming to implement clever ideas and help magic stay abreast of fabrication technology. However, it is the well thought-out core algorithms which lend to magic the greatest part of its popularity. Magic is widely cited as being the easiest tool to use for circuit layout, even for people who ultimately rely on commercial tools for their product design flow.

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Xilinx ISE Design suite 10.1

Xilinx Integrated Software Environment (ISE) is a powerful yet flexible integrated design environment that allows you to design Xilinx FPGA and CPLD devices from start to finish. ISE includes our world class design entry, synthesis and implementation tools delivering the industry's fastest place and route times, highest performance, and most advanced design methodologies.

Project Navigator is the user interface that helps you manage the entire design process including design entry, simulation, synthesis, implementation and finally download the configuration of your FPGA or CPLD device.

The following is an outline of the features offered in ISE.

Design Entry

• HDL Editor
• StateCAD State Machine Editor
• Schematic Editor - Engineering Capture System (ECS)
• CORE Generator

Synthesis

• XST - Xilinx Synthesis Technology
• Integration with LeonardoSpectrum from Mentor Graphics, Inc.
• Integration with Synplify from Synplicity, Inc.

Simulation

• HDL Bencher Testbench Generator
• Integration with ModelSim Simulator from Model Technology, Inc.

Implementation

• Translate
• MAP
• Place and Route (PAR)
• Floorplanner
• FPGA Editor
• Timing Analyzer
• XPower
• Fit (CPLD only)
• Chipviewer (CPLD only)

Device Download and Program File Formatting

• BitGen
• iMPACT

Download the Xilinx ISE 10.1 design suit from Here

AMD and Intel Announce Settlement of All Antitrust and IP Disputes

Intel Corporation and Advanced Micro Devices (NYSE: AMD) today announced a comprehensive agreement to end all outstanding legal disputes between the companies, including antitrust litigation and patent cross license disputes.

In a joint statement the two companies commented, "While the relationship between the two companies has been difficult in the past, this agreement ends the legal disputes and enables the companies to focus all of our efforts on product innovation and development."

Under terms of the agreement, AMD and Intel obtain patent rights from a new 5-year cross license agreement, Intel and AMD will give up any claims of breach from the previous license agreement, and Intel will pay AMD $1.25 billion. Intel has also agreed to abide by a set of business practice provisions. As a result, AMD will drop all pending litigation including the case in U.S. District Court in Delaware and two cases pending in Japan. AMD will also withdraw all of its regulatory complaints worldwide. The agreement will be made public in filings with the Securities and Exchange Commission.

http://www.amd.com/us/press-releases/Pages/amd-press-release-2009nov12.aspx

ELECTRIC VLSI Design Software

The Electric^TM VLSI Design System is an open-source Electronic Design Automation (EDA) system that can handle many forms of circuit design, including:

• Custom IC Layout
• Schematic Capture (Digital and Analog)
• Textual Languages such as VHDL and Verilog
• ....and much more.

The Electric VLSI Design System is a highly flexible and powerful system that can handle many different types of circuit design (MOS, Bipolar, schematics, printed circuitry, hardware description languages, etc.) It handles geometry at any angle (not just Manhattan) and can even handle curves.

Layout is done by placing and wiring electrical components. Although this is standard practice for schematics, it is unusual for chip layout. However, because of this style of design, Electric understands chip layout at a more sophisticated level, and can aid in design to an unprecedented degree.

Electric has many analysis tools, including design-rule checking, simulation, and network comparison. Electric has many synthesis tools, including routing, compaction, silicon compilation, PLA generation, and compensation.

The user interface is quite sophisticated and runs on all popular workstations (Windows, Macintosh, and UNIX). It also provides interpretive languages for advanced users.

The software is freely available at www.staticfreesoft.com

VLSI Interview Questions-1

1. what is the difference between mealy and moore state-machines
2. how to solve setup and hold violations in the design
3. what is antenna violation & ways to prevent it
4. we have multiple instances in RTL(Register Transfer Language), do you do anything special during synthesis stage
5. what is tie-high and tie-low cells and where it is used
6. what is the difference between latches and flip-flops based designs
7. what is High-Vt and Low Vt cells
8. what is LEF mean?
9. what is DEF mean?
10. steps involved in designing an optimal padring
11. what is metastability and steps to prevent it
12. what is local-skew, global skew and useful skew
13. what are the various timing-paths which i should take care in my STA runs?
14. what are the various components of leakage-power
15. what are the various yield losses in the design
16. what is meant by virtual clock definition and why do i need it
17. what are the various variations which impacts timing of the design
18. what are the various Design constraints used, while performing synthesis for a design
19. specify few verilog constructs which are not supported by the synthesis tool
20. what are the various capacitances with an MOSFET?
21. Vds-Ids curve for an MOSFET, with increasing Vgs
22. explain basic operation of an MOSFET
23. what is channel length modulation
24. what is body effect
25. what is latchup in CMOS design and ways to prevent it?
26. what are the various design changes you do to meet design power targets
27. what is meant by library characterization
28. what is meant by wireload model
29. what are the measures to be taken to design for optimized area
30. what all will you be thinking while performing floorplan
31. what are the measures in the design taken for meeting signal integrity targets
32. what are the measures taken in the Design achieving better yield
33. what are the measures or precautions to be taken in the design when the chip has both analog and digital portions.
34. what are the steps incorporated for Engineering Change order[ECO]
35. what are the steps performed to achieve Lithography friendly Design
36. what does synthesis mean?
37. what are the pre-requistes to perform synthesis
38. can you explain the synthesis flow
39. what are the various ways to reduce clock insertion delay in the design
40. what are the various functional verification methodologies
41. what does formal verification mean
42. how will you time the output path in STA
43. how will you time the input path in STA
44. what is false path mean in STA and in what scenarios falsepath can come
45. what does multicycle path mean in STA and in what scenarios MCP can come
46. what are source synchronous paths in STA
47. Assume there is a specific requirement to preserve the logic during synthesis , how will you achieve it.
48. we have multiple instances in RTL, do you do anything special during synthesis stage
49. what do you call an event and when do you call an assertion.
50. what is difference between FPGA and ASIC.

Solutions to these questions will be provided on request.

mail me at vlsi.vishal@gmail.com