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In most cases today, IC power analysis efforts are mainly focused at signoff. Even though some place and route (P&R) solutions provide simple checks at the floor planning stage, there are a lot of opportunities to improve power analysis capabilities during design, and to align and integrate these with the signoff tools and the overall design flow. 

Figure 1. A full-flow approach to power analysis during IC physical
design. 

Although every semiconductor company handles power analysis slightly differently, Figure 1 shows an idealized approach in which power analysis is embedded across the entire IC physical design flow. IC designers get their specifications from a cross-functional architecture power constraints definition, which is often called the “power budget.” This budget, which typically is fixed before any new IC implementation is started, specifies the maximum power permitted for the system, the board and the IC packages. At this point, the budget is essentially a rough estimate based on the know-how and experience of the IC, package and board engineers involved in the requirements definition for each new product development project. Once a high level budget is defined, it can be used to project the expected current flow and a power grid (PG) definition can be derived and partitioned into more detailed domains within the IC. The power grid should be able to accommodate the maximum expected current flows without a significant voltage drop given a design margin of around 10%. This sets the constraints for IC physical design implementation in a conventional P&R flow, which ends in a final power signoff analysis that validates the design against the power budget. Unfortunately, the process does not always proceed in this idealized, linear fashion. When the budget estimates are off, or the implementation is more difficult and power hungry than anticipated, “making ends meet” can become painful and lengthy.  This article describes in more detail how power constraints are enforced in the design flow and highlights areas of opportunity to improve the results, eliminating surprises, with a more robust power analysis capability.

Signoff Power Analysis

Introduction

Today's classrooms, including studios, laboratories, auditoriums, and other indoor environments, have a wide variety of physical structures that support and facilitate student learning. There is no perfect classroom physical design to accommodate all types of academic activities. Because students learn in diverse ways, higher education administrators must realize that classrooms should be designed to promote various ways in which students acquire knowledge (The L-Shaped Classroom, 2007). Well-designed classrooms not only promote teamwork and interest in student learning, but also encourage active class participation (Niemeyer, 2003). Although college classrooms with permanently attached seating and furnishings are beyond the instructors' control, they may partially influence student evaluations of college instructors in terms of the overall teaching effectiveness and performance (Safer et al., 2005).

Students are not the only ones who feel helpless and hopeless when the built classroom environment is beyond their control (Veltri et al., 2006). Faculty also feel helpless and sometimes even fearful (Veltri et al., 2006). Niemeyer (2001) does not believe faculty should be fearful of their teaching environment. Unfortunately, classrooms are not always a location that empowers faculty and that is conducive to student learning. Physical settings and factors can motivate or discourage many room occupants (Lackney, 1999). Hence, a classroom's arrangement of visual, furniture, and equipment should be carefully considered in order to empower both instructors and students (Niemeyer, 2001).

After 4 months of articles about data modeling, we're getting close to a functional database. I started this data modeling series with "Data Modeling" (April 2000), which discussed how to gather project requirements. I followed up with "Process Modeling" (May 2000), which reviewed process modeling and demonstrated my own variation of data-flow diagramming to illustrate what happens as data moves through the system. Then in "Entity Modeling" (June 2000), I developed a concept model, or entity relationship diagram (ERD), of the database. Last month, in "Logical Modeling" (July 2000), I translated that ERD into a logical model, which is a closer representation of the evolving database. This month, I develop a physical design that takes us one more step toward a working database.

A physical design is a specification for database implementation. At this phase of development, you must know the database platform you're going to use—perhaps SQL Server 7.0 on Windows NT Server 4.0, Microsoft Access on the desktop, Oracle on the mainframe, or some other platform. To create a physical design, you pull together all the specifications and models you've created so far, then modify and optimize them for your target platform. For example, you need to modify all column properties, including data types, so that they're specific to your target environment. You can add extra columns that don't appear in the conceptual or logical models, such as flag columns and timestamp columns that facilitate data processing. You also need to size the database, analyze data volume and use, incorporate any replication or distribution plans, and select candidate columns for indexing. If you're thinking ahead, you'll also determine user roles (groups), logins, and security permissions; requirements for data retention (archiving plans); and failover and backup and recovery plans.

Creating a Physical Design

The physical design is a composite of models that, taken together, form a complete or near-complete specification for implementing a database. So what does a physical design look like? Part of it, the piece we ordinarily call the "physical model," looks like an expanded ERD, as Figure 1, page 62, shows. Other parts, such as the Data Volume Analysis model and the Security Matrix, also look familiar.

Abstract :

The hard IP cores, as hard modules, should be pre-placed or placed inside the soft modules as the first step in VLSI physical design. Normally, automatic placer can not obtain good results because some aspects, such as power, the connection with the standard cells, halo and the location of pins, are not under consideration in the placement algorithm, which is true especially for the complex design containing more IP cores with different sizes. This paper proposes a hard IP core placement method, adopting manual adjustment steps, such as rotation, removing overlap and change the placement obviously, based on the results of the automatic placer. An AVS HDTV decoder chip and a test small chip are implemented by this method. The application results have proved that this method is optimum and practical in VLSI physical design.

1. INTRODUCTION

With the increasing of the design complexity and the popular adoption of IP cores, the module placement, as one of the main tasks of floorplanning at the early stage of VLSI physical design, has become more important than before. The modules are classified as two types: hard module and soft module. The hard IP cores, which usually have fixed area and shape, are regarded as hard modules at placement stage.

There are several placement algorithms [1][2][3] and most of automatic placers are developed on them. Placement constraints, such as clustering constraint [4], boundary constraint [5] and abutment constraint [6], are efficient for users to restrict the position of certain modules and to improve the performance of placers. These placers can deal with the placement of both hard module and soft module only consisting of standard cells.

However, there are still some disadvantages for these automatic placers to place the hard IP cores. At first, these tools deal with the parameters, such as area, routability and timing, but another critical issue of power can not be considered. In addition, the connection of the pre-placed hard IP cores with standard cells, the location of pins and the halo, are not taken into account in placement algorithms. Furthermore, the size of hard IP cores is varied, and the number of hard IP cores in VLSI design has increased distinctly. All of these factors limit the application and usefulness of many automatic placers for large and complex VLSI design in practice.

A hard IP core placement method is proposed in this paper, which takes the issues mentioned above into consideration. This method combines the automatic placement with manual adjustments, in order to optimize the hard IP core placement effect. The manual adjustments includes rotation and the overlap resolving, both of them change the location only slightly, and changing the location of hard IP cores obviously after the later steps in physical design. This method was implemented in a small test chip and an AVS HDTV decoder chip. The application results proved that the method is useful and practical.

The remainder of the paper is organized as follows: Section 2 describes the hard IP core placement method. Experimental results are presented in section 3. Section 4 draws a conclusion.

2. HARD IP CORE PLACEMENT METHOD

For an actual VLSI design, which is viewed as a set of hard IP cores and soft modules according to the hierarchy at the module placement stage, the automatic placer might not produce good results because of various factors. The main reason is that the location of hard IP cores usually has a priority. These modules are pre-placed or placed inside soft modules, and then the standard cells are subject to be placed in the rest area of relative soft modules. As a result, the connectivity between the standard cells and the hard IP cores will not be taken into consideration unless the standard cells are pre-placed. At the same time, the power routing plan is more complicated because the power grids will be broken by the presence of these modules, which make the IR drop more serious. In addition, the shape and the location of pins of hard IP cores are varied with the foundry. And the overlap of the halos is difficult to be treated with due to the different values of the halo.

In order to solve the problems mentioned above, this paper proposes a hard IP core placement method, which does efficient manual adjustments based on the initial automatic placement of hard IP cores, as the Figure 1 shows. For the sake of clarity, only the steps relating to the hard IP core placement are drawn and connected in the figure. The manual adjustment mainly includes two styles. One is change the location slightly, such as rotation and removing overlap. The other is to change the location obviously after the following steps in physical design, such as power routing, standard cells placement and routing.


Figure 1. The hard IP core placement method

This hard IP core placement method is a general method and the steps may change a little according to the shape and the pin location of the IP cores. The IP cores have two mainly shapes: square and rectangle. The rotations of the rectangle IP cores may cause overlap, while the rotations of the square IP cores are not. Furthermore, the pins of the hard IP cores located differently, such as in corner, in one side and in two sides. The manual adjustment steps are presented as follows.

2.1 Rotation

The initial automatically placed hard IP cores need be rotated on condition that described as follows. Firstly, rotating the hard IP cores by users according to the locations of pins could reduce the wire length between the IP cores themselves. Secondly, the location of pins also have a directly relationship with the connection of relative standard cells. Rotation could reduce the congestion, improve the routability between hard IP cores and standard cells, and avoid the DRC violations such as spacing and short. However, the requirement of this rotation only can be obtained after the standard cells are placed or the route is finished. For a complex design, the rotation should get a tradeoff between all these factors mentioned above. Furthermore, the power grid will be cut off when encounters the hard IP cores, these modules should be rotated, if these IP cores are rectangle, to decrease or avoid the influence on power routing.

The 90°or 270° rotation of hard IP cores may cause overlap of the halo or themselves, if the IP cores are rectangle and the distances between them are not large enough. The overlap should be resolved later.

2.2 Removing overlap

Removing overlap is the next step in this method. Most of the overlap present to halo, which is popular and useful in current VLSI design. Halo, the area that prevents the placement of the standard cells within, is added around the hard IP cores in order to provide additional routing space and reduce congestion. The number of the halo is estimated according to the design itself, and the width of halo in the four sides may different. However, the halo is not taken into consideration in placement algorithm, which results in the overlap of hard IP cores are avoided whereas the halo may overlap. Furthermore, the rotation may cause overlap of the halo or cores themselves if the hard IP cores are not square.  

The overlap of the hard IP cores will cause manufacture error, while the overlap of halo may cause placement error. And either overlap means the distance between the hard IP cores are too small to route or insert standard cells. The approach to remove the overlap is moving the hard IP cores which have the overlap to be separate manually as short as possible, while the general locations are changeless based on the initial placement.

2.3 Change the location obviously

When the slightly change steps are finished, the following steps in physical design will be implemented as typical physical design flow. Then, if there still have some timing violations, DRC violations or IR drop violations caused by the placement of some hard IP cores, change the location obviously step should be implemented. This step includes increase the distance of hard IP cores as long as need, exchange the location of several hard IP cores and move hard IP cores from one corner to another corner, according to the practical design. The distance of the hard IP cores could be estimated according to the target usage and the shape of the soft module, the number of hard IP cores that be placed inside this soft module, the shape and the pin locations of the hard IP cores, and the size of the soft module. 

In practice, an obviously change of the location could resolve certain violations, but may cause the other violations because the complicated relationship of the design parameters. On this condition, this step need be done several times, in order to solve all the violations and get a tradeoff of the design parameters. The number of iteration depends on the design scale, design complexity, the number of hard IP cores, the requirement of the design parameters and the experience of the designers.

3. EXPERIMENTAL RESULTS

This method was implemented in a small test chip (chip 1) and an AVS HDTV decoder chip (chip 2). The RAM and ROM IP cores in these two chips, which are regarded as hard IP cores, should be pre-placed and placed inside the soft modules with certain area. What’s more, the IO cells are arranged and the locations of the soft modules are fixed before the hard IP cores are placed in chip 2. The design parameters of these two chips are listed in Table 1 and the manual adjustments of them are compared in Table 2. Furthermore, the application results of this method were compared with the automatic placement, which are shown in Figure 2 and Figure 3, and the relative data are listed in Table 3 and Table 4.  

The AVS HDTV decoder chip has been delivered to the EDA center and under tape out now.

 Table 1. The design parameters of two chips

Figure 2. The compare hard IP core placement results of the test chip.


Figure 3. The compare results of the AVS HDTV decoder chip.

From these tables, we can get the conclusion that for these two different chips, the application of this method could obtain better results than the automatic placement in design parameters, such as timing, congestion, routability and IR drop.

4. CONCLUSION 

A hard IP core placement method is proposed and used in designing a test chip and an AVS HDTV decoder chip. The designed results indicate that the proposed method is useful and helpful for complex VLSI physical design.  

When designing a product that operates off of a small battery, low power consumption is extremely critical. A well-designed power system can be a key differentiator for a competitive low-power product. Designing an ultra-low-power system, on the other hand, can be a highly complex undertaking. A design team needs to balance and integrate a variety of low-power design approaches and techniques to achieve their goals. Using a combination of multiple power domains and operating voltages, along with thorough statistical analysis, a low power product can be designed to provide a competitive advantage.

Any company that develops products that operate off a small battery can benefit from considering well-integrated, physical design practices for low power consumption design targets. Wireless sensors, mesh networks, wearables, Bluetooth devices, Internet of Thing (IoT) devices, hearing aids, mobile phone audio/video processing capabilities, tablets and headsets all require an optimized approach to achieve ultra-low power.

So, what is it that these ultra-low-power products need? Often, a minimum clock rate will be used meet performance goals. Higher threshold voltage (VT) devices may be used to minimize leakage. Perhaps multiple clock domains, multiple power domains and/or multiple operating voltages will be part of the low-power design solution. Lower operating and standby voltages lead to much lower overall power consumption; however, multiple power domains also result in a complex SOC (system on a chip) power structure.