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    Monday, November 19, 2007

    The ASIC Factory ( Part 3) : The Toyota Way For Fabless ASICs

    This post is part 3 of the application of the 14 principles of the Toyota Way to the ASIC design process. You can find Part 1 and Part 2 here or click on principles #1 through #4 below.

    #1. Base your management decisions on a long-term philosophy, even at the expense of short-term financial goals.

    Create a continuous process flow to bring problems to the surface.

    Use "pull" systems to avoid overproduction.

    #4. Level out the workload (heijunka). (Work like the tortoise, not the hare).

    #5. Build a culture of stopping to fix problems, to get quality right the first time.

    Most ASIC design projects go through concurrent evolution of RTL, floorplan and package. Sometimes, for new IP, we can expect that the IP vendor will provide multiple drops of increasing maturity as the project progresses. Given this state of affairs, does this principle imply that we must freeze RTL before running synthesis? or that the IP must be solid before the RTL is designed? No! Quality is relative to expectations and point of view. For synthesis, the meaning of high-quality IP might be that the timing information contained in the libraries are final or close to final. This would allow synthesis to proceed without nasty timing surprises down the line. The area of the IP is immaterial. The IP need not even have a dummy placeholder LEF. For place-and-route, high quality can be taken to mean fixed IP macro size and fixed pin locations. The GDSII that matches the size and pin locations can come later during the final DRC runs. Clearly, this principle does not preclude usage of a concurrent evolution methodology.

    What we seek to prevent is the propagation of low quality (as defined by expectations) in the ASIC flow. Quality is a box that is centered around a target number (area in sq.mm, for example) and bounded on either side by tolerance limits (within 5% of final design area, for example). Anything within the box is of acceptable quality. Anything outside the box is of low quality. Low quality RTL, for example, can be defined as RTL that does not include blocks with large area impact.
    When the designer does not fully capture the area of the design, the place-and-route strategy will suffer. When the design grows by a million gates over the space of a few iterations, your floorplan and powerplan go out of the window. In fact, you might find yourself in the unenviable position of having to switch from a flat place-and-route strategy to a hierarchical one.

    Low quality inputs lead to low quality outputs. Rather than waste time and effort downstream, do the right thing: Get quality right the first time around.

    #6. Standardized tasks and processes are the foundation for continuous improvement and employee empowerment.

    The benefits of standardization are many.

    • Standardization of processes is essential to meet quality constraints. When each engineer has his or her own way of doing things, the quality of the output varies widely. Further, there is a high probability of the introduction of errors. When you diligently follow a proven process that is known to provide quality output, the chance for errors are minimized. A standard synthesis script that is to be used across all projects is an example of a standardization that makes it easy to meet quality constraints.
    • Standardization makes it easier to map out and subsequently meet schedules. When you have fully mapped the path from RTL to GDSII, you already have an idea of the critical execution path and how long the process will take. In fact, through standardization, scheduling methodology itself will be a well-documented process.
    • Standardization is the first step towards automation. When your processes are standardized with respect to inputs, outputs and measurable quality metrics, you already have a specification that can be used to automate the menial and repeatable sections of the ASIC design process.
    • Standard processes are required to be fully specified before one attempts any process improvement strategies. Before you can improve, you must know what it is you're improving upon. Further, when the process improvements suggested are "proven", they can be incorporated as a part of the standard design process. If you find (and prove) a way to improve simulation runtime by 15%, it is easy for everyone in the organization to reap the benefits if this improvement is incorporated into the standard ASIC design process.
    • Standardized processes that are accessible at all levels serve to empower employees. When everybody knows what needs to be done and what is important, they have a checklist against which to evaluate a situation and their proposed response. Employees are empowered because they are able to take decisions with greater independence. Further, they have the confidence that the decisions made are both right and justifiable in light of set processes.

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