Cell Placement Research Articles

Force-Directed Methods for Generic Placement

This paper describes the implementation of a wire length-driven force-directed placer named FDP for generic placement. Specifically, it describes efficient force computation for cell spreading, numerical instabilities during force-directed placement, a means to avoid instabilities, and metrics for proper assessment of cell distribution throughout the placement region. It demonstrates that one of the greatest impediments to achieving high-quality placements using a force-directed placer lies in the large amount of cell overlap present in initial placements. This overlap makes the determination of cell ordering difficult and can lead to the inadvertent separation of highly connected cells. It is shown that median improvement and multilevel clustering improve cell ordering and aid in wire length minimization. Numerical results are presented for both standard cell and mixed-size placement problems. For standard cell problems, the tool generates placements that are, on average, 3% better than Capo9.0, but 5% worse than FengShui2.6. For mixed-size problems, FDP generated placements that are, on average, 2%-5% better than Capo9.0 and -5%--2% better than Fengshui2.6, depending on the presence (or absence) of pin offsets. Run times for FDP are higher than both Capo9.0 and FengShu2.6, although reasonable

Min-cut floorplacement

Large macro blocks, predesigned datapaths, embedded memories, and analog blocks are increasingly used in application-specific integrated circuit (ASIC) designs. However, robust algorithms for large-scale placement of such designs have only recently been considered in the literature. Large macros can be handled by traditional floorplanning, but are harder to account for in min-cut and analytical placement. On the other hand, traditional floorplanning techniques do not scale to large numbers of objects, especially in terms of solution quality. The authors propose to integrate min-cut placement with fixed-outline floorplanning to solve the more general placement problem, which includes cell placement, floorplanning, mixed-size placement, and achieving routability. At every step of min-cut placement, either partitioning or wirelength-driven fixed-outline floorplanning is invoked. If the latter fails, the authors undo an earlier partitioning decision, merge adjacent placement regions, and refloorplan the larger region to find a legal placement for the macros. Empirically, this framework improves the scalability and quality of results for traditional wirelength-driven floorplanning. It has been validated on recent designs with embedded memories and accounts for routability. Additionally, the authors propose that free-shape rectilinear floorplanning can be used with rough module-area estimates before logic synthesis

SimE/TS fuzzy hybrid for multiobjective VLSI placement

A hybrid heuristic for multiobjective VLSI cell placement is presented, which draws from the memory concept of Tabu search (TS) and the goodness feature of Simulated Evolution (SimE). Experimental results using ISCAS-89 benchmark circuits illustrate improvement in quality as compared to our best canonical TS implementation.

An efficient quadratic placement based on search space traversing technology

A very large-scale standard cell placement problem has too complicated solution space for conventional analytical quadratic placement methods to achieve the “optimal” or near-optimal solution in it. The rugged terrain of solution space makes those methods easy to get stuck at local optima. In this paper, a novel quadratic placement based on search space traversing technology is proposed to search the optimal or near-optimal solution. This method first employs a pre-partitioning to cut down the problem scale and reconstruct the problem structure, and then combines the Lagrange relaxation method and the Lagrange multipliers method together in quadratic placement to solve the global placement. Finally, after eliminating overlaps, a full-chip force-directed post-adjustment is employed to reduce the negative effect of pre-partitioning. Experimental results on benchmarks show encouraging results.

Cell density requirements for UMTS network planning

Cell planning for the Universal Mobile Telecommunications System (UMTS) is challenging due to the interrelationships between coverage, capacity, service requirements and the power control mechanism inherent to the system. This means that classical coverage models, adopted from second generation systems are insufficiently detailed for UMTS cell planning purposes. An important stage in the cell planning process is network dimensioning to determine the required cell density. This can be used to guide the deployment of infrastructure and assess the optimality of operational networks. Highly efficient cell placement is important for UMTS since transmission infrastructure and site costs will account for a substantial proportion of total network costs. In this paper, we show how link budget and capacity analysis can be used to derive estimates on the minimum number of cells required to support a particular mix of UMTS services. For typical service requirements, we show how key factors in the model, such as service type, load, propagation environment and system parameters affect the minimum required cell density. We also demonstrate points at which cell density requirements change dependency on coverage and capacity based requirements.

Navigating Register Placement for Low Power Clock Network Design

With VLSI design development, the increasingly severe power problem requests to minimize clock routing wirelength so that both power consumption and power supply noise can be alleviated. In contrast to most of traditional works that handle this problem only in clock routing, we propose to navigate standard cell register placement to locations that enable further less clock routing wirelength and power. To minimize adverse impacts to conventional cell placement goals such as signal net wirelength and critical path delay, the register placement is carried out in the context of a quadratic placement. The proposed technique is particularly effective for the recently popular prescribed skew clock routing. Experiments on benchmark circuits show encouraging results.

Establishing and maintaining axial growth: wall mechanical properties and the cytoskeleton

Organ morphology depends on cell placement and directional cell expansion. Microtubules are involved in both of these processes so genetic approaches to understand the role microtubules play in organ expansion are not straightforward. Our use of the temperature-sensitive mor1-1 mutants led to the surprising discovery that Arabidopsis thaliana (L.) Heynh. root cells can establish and maintain transverse cellulose texture without well organized microtubule arrays. This work also demonstrated that cells can lose the ability to expand anisotropically without losing transversely oriented cellulose microfibrils. We suggest that microtubule disruption affects the cell's ability to generate long cellulose microfibrils, which may be essential for achieving growth anisotropy. Thus organ shape may depend not only on the orientation but also on the relative length of cellulose microfibrils during axis establishment and growth. More recent work has shown an important correlation between microtubule organization and the deposition patterns of the glycosylphosphatidylinositol (GPI)-anchored wall protein COBRA. Loss of microtubule organization is associated with the dissipation of transverse banding patterns of COBRA, suggesting that COBRA's function in maintaining anisotropic expansion may be microtubule-dependent.

FtsZ mutations affecting cell division frequency, placement and morphology in Bacillus subtilis

A key event in cytokinesis in bacteria is the assembly of the essential division protein FtsZ into ring-like structures at the nascent division site. FtsZ is the prokaryotic homologue of tubulin, and is found in nearly all bacteria. In vitro, FtsZ polymerizes in the presence of GTP to form higher-ordered polymers. FtsZ consists of two domains, with the GTP-binding site located in the N-terminal domain. The less-conserved C-terminal domain contains residues important for GTP hydrolysis, but its overall function is still unclear. This paper reports the development of a simple strategy to generate mutations in the essential division gene ftsZ. Nine novel and viable ftsZ mutants of Bacillus subtilis are described. Eight of the mutations would affect the C-terminus of FtsZ. The collection of mutants exhibits a range of morphological phenotypes, ranging from normal to highly filamentous cells; some produce minicells, or divide in a twisted configuration; one mutation has a temperature-sensitive effect specifically impairing sporulation. The sites of the amino acid changes generated by the mutations could be informative about FtsZ function and its protein-protein interactions.

Time-phased creation of hybrid manufacturing systems

This paper develops a comprehensive method for transforming pure functional manufacturing shops into hybrid production systems that comprise both cellular and functional areas. The facility redesign approach first derives the layout of the work centers within each cell and then places the cells within existing departments according to a time-phased implementation plan. The incremental cell implementation is dictated by budget constraints that limit the allowable investment in each fiscal period. The goal is to maximize the net benefit from cell implementation, expressed as the difference between the savings in material handling effort and the cost of machine rearrangement. An explicit enumeration scheme provides the optimal intra-cell layout. The problems of cell placement and implementation sequence are integrated in an integer programming formulation. The decomposition of the mathematical model motivates a space search approach, which generates an optimal solution. All algorithms are integrated and used to transform the functional shop of a large manufacturer into a hybrid production area. The results illustrate that substantial benefits can be realized even with a conservative multiperiod implementation plan.

Mixed block placement via fractional cut recursive bisection

Recursive bisection is a popular approach for large scale circuit placement problems, combining a high degree of scalability with good results. In this paper, we present a bisection-based approach for both standard cell and mixed block placement; in contrast to prior work, our horizontal cut lines are not restricted to row boundaries. This technique, which we refer to as a fractional cut, simplifies mixed block placement and also avoids a narrow region problem encountered in standard cell placement. Our implementation of these techniques in the placement tool Feng Shui 2.6 retains the speed and simplicity for which bisection is known, while making it competitive with leading methods on standard cell designs. On mixed block placement problems, we obtain substantial improvements over recently published work. Half perimeter wire lengths are reduced by 29% on average, compared to a flow based on Capo and Parquet; compared to mPG-ms, wire lengths are reduced by 26% on average.

Implementation and extensibility of an analytic placer

Automated cell placement is a critical problem in very large scale integration (VLSI) physical design. New analytical placement methods that simultaneously spread cells and optimize wirelength have recently received much attention from both academia and industry. A novel and simple objective function for spreading cells over the placement area is described in the patent of Naylor et al. (U.S. Pat. 6301693). When combined with a wirelength objective function, this allows efficient simultaneous cell spreading and wirelength optimization using nonlinear optimization techniques. In this paper, we implement an analytic placer (APlace) according to these ideas (which have other precedents in the open literature), and conduct in-depth analysis of characteristics and extensibility of the placer. Our contributions are as follows. 1) We extend the objective functions described in (Naylor et al., U.S. Patent 6301693) with congestion information and implement a top-down hierarchical (multilevel) placer (APlace) based on them. For IBM-ISPD04 circuits, the half-perimeter wirelength of APlace outperforms that of FastPlace, Dragon, and Capo, respectively, by 7.8%, 6.5%, and 7.0% on average. For eight IBM-PLACE v2 circuits, after the placements are detail-routed using Cadence WRoute, the average improvement in final wirelength is 12.0%, 8.1%, and 14.1% over QPlace, Dragon, and Capo, respectively. 2) We extend the placer to address mixed-size placement and achieve an average of 4% wirelength reduction on ten ISPD'02 mixed-size benchmarks compared to results of the leading-edge solver, FengShui. 3) We extend the placer to perform timing-driven placement. Compared with timing-driven industry tools, evaluated by commercial detailed routing and static timing analysis, we achieve an average of 8.4% reduction in cycle time and 7.5% reduction in wirelength for a set of six industry testcases. 4) We also extend the placer to perform input/output-core coplacement and constraint handing for mixed-signal designs. Our paper aims to, and empirically demonstrates, that the APlace framework is a general, and extensible platform for spatial embedding tasks across many aspects of system physical implementation.

Zonal ICCP System Control Interactions

To date much work has been done on modeling shipboard impressed current cathodic protection (ICCP) systems. The emphasis has been on system performance: the systems’ ability to maintain the hull at a constant potential value. Reported system design work has dealt mainly with anode number, anode placement, subdividing the overall system into power supply zones (anodes connected to a single power supply with a controlling reference cell) and reference cell placement. As electronic and hardware advances are incorporated into new ship designs the system control algorithms are evolving. In general, system control algorithms can range from simple one point feedback to complex multiple input-multiple-output that subdivide the structure into small regions. Multiple input-multiple-output systems provide the ability to fine tune in order to maintain uniform values throughout the structure. It has long been observed, both experimentally and on shipboard, that even simple ICCP systems with two or three power supply zones show zonal interactions. This work uses a model ship geometry, computational methods and experimental physical scale model results to further the understanding of the interaction between individual power zones on a typical shipboard ICCP system.

Performance-driven placement procedure for low power

Deep-Sub-Micron (DSM) technologies of 0.18 μm and below enable the integration of logical circuits having more than 10 million gates. In such a DSM technology, it is important to consider reducing power consumption, improving interconnection delay, and dispersing wire congestion at the initial phase of layout design. In this paper, we proposed a novel performance-driven placement algorithm. The proposed algorithm based on Genetic Algorithm (GA) has a two-level hierarchical structure. For selection control, new objective functions are introduced for reducing power consumption, improving interconnection delay, and dispersing wire congestion. Studies on floor planning and cell placement have been reported as being applications of GA to the LSI layout problem. However, no studies have ever seen the effect of applying GA with consideration of power, delay, and congestion. Results show improvement of 11.7% for the total wire length of the nets with high SW rate, 22.5% for the worst path delay, and 15.9% for wire congestion on average. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 56–65, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20057

Effective Memetic Algorithms for VLSI Design = Genetic Algorithms + Local Search + Multi-Level Clustering

Combining global and local search is a strategy used by many successful hybrid optimization approaches. Memetic Algorithms (MAs) are Evolutionary Algorithms (EAs) that apply some sort of local search to further improve the fitness of individuals in the population. Memetic Algorithms have been shown to be very effective in solving many hard combinatorial optimization problems. This paper provides a forum for identifying and exploring the key issues that affect the design and application of Memetic Algorithms. The approach combines a hierarchical design technique, Genetic Algorithms, constructive techniques and advanced local search to solve VLSI circuit layout in the form of circuit partitioning and placement. Results obtained indicate that Memetic Algorithms based on local search, clustering and good initial solutions improve solution quality on average by 35% for the VLSI circuit partitioning problem and 54% for the VLSI standard cell placement problem.

Automatic cell placement for quantum-dot cellular automata

Quantum-dot cellular automata (QCA) is a novel nano-scale computing mechanism that can represent binary information based on spatial distribution of electron charge configuration in chemical molecules. In this paper we develop the first cell-level placement of QCA circuits under buildability constraints. We formulate the QCA cell placement as a unidirectional geometric embedding of k-layered bipartite graphs. We then present an analytical and a stochastic solution for minimizing the wire crossings and wire length in these placement solutions.

Oriented Schwann cell monolayers for directed neurite outgrowth.

Schwann cells are an important component of the peripheral nervous system and participate in peripheral nerve regeneration. They create a supportive environment for neurite outgrowth by releasing trophic factors and up-regulating permissive molecules on their surface. In addition, Schwann cells are able to self-organize into linear arrays in vitro and in vivo, suggesting a possible role in neurite guidance. Previously, we showed that Schwann cell placement and orientation in subconfluent cultures can be controlled using microlithographically patterned laminin substrates (Thompson, D. M., and H. M. Buettner. Tissue Eng. 7(3):247-266, 2001). In the current study, these substrates were used to create oriented Schwann cell monolayers. Both Schwann cell orientation and coverage were quantified in response to seeding density, culture medium, and micropattern dimensions. In serum-free medium, increasing the seeding density yielded a linear increase in coverage of the substrate area but decreased cell alignment. In an alternate approach, Schwann cells were first seeded in serum-free medium at moderate seeding density, allowed to align, then expanded in serum-containing growth medium. This produced complete coverage without large seeding densities while preserving alignment to the micropattern. Alignment and coverage were unaffected by micropattern dimensions. This work provides a useful methodology for investigating Schwann cell guidance effects on growing neurites.

Biopuces pour le traitement de cellules vivantes : micromanipulation des cellules par voie électrique ou microfluidique

After a brief overview of the state of the art in the domain of cell biochips, and more particularly, the usual methods for cell placement and characterization on a chip, our research on highly parallelized cell placement on a chip is presented. Single cell arraying methods, using dielectrophoresis effects, or microfluidic effects produced by bulk micromachined sub-micrometric capillaries are compared. Target applications of such cell biochips cover the domain of gene transfer on a large population of cells, parallelized cell sorting, or drug high-throughput screening on living cells. To cite this article: B. Le Pioufle et al., C. R. Physique 5 (2004).

Beat the competition

Working within the application-specific integrated circuit (ASIC) industry, time to market is very important. With very deep submicron (VDSM) processes, issues with timing enclosure, cell placement efficiency, the antenna effect, signal integrity, etc., have impacted our ability to meet market requirements in a timely manner. By focusing on the design process, two of the major issues, the antenna problem and cell placement efficiency, can be addressed. I propose using knowledge-based priority placement (KBPP), which utilizes design knowledge to simplify those two issues.

Performance Driven Placement Procedure for Low Power

Deep-Sub-Micron (DSM) technologies of 0.18 μm and below enable the integration of logical circuits having more than 10 million gates. In such a DSM technology, it is important to consider reducing power consumption, improving interconnection delay, and dispersing wire congestion at the initial phase of layout design. In this paper, we proposed a novel performance-driven placement algorithm. The proposed algorithm based on Genetic Algorithm (GA) has a two-level hierarchical structure. For selection control, new objective functions are introduced for reducing power consumption, improving interconnection delay, and dispersing wire congestion. Studies on floor planning and cell placement have been reported as being applications of GA to the LSI layout problem. However, no studies have ever seen the effect of applying GA with consideration of power, delay, and congestion. Results show improvement of 11.7% for the total wire length of the nets with high SW rate, 22.5% for the worst path delay, and 15.9% for wire congestion on average. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 56–65, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20057

Comprehension of attachment and multiplication properties by observing individual cell behaviors in anchorage-dependent culture

The behavioral properties of cell attachment and division were characterized by direct observation of individual cells in the culture of murine fibroblasts. At the cell attachment stage in the culture for early 10 h, the extent of cell spreading, which was defined as a ratio of the projected area of each cell against its saturated value, had a relatively broad distribution at 0.25 h, and it shifted to a higher level with elapsed time up to 10 h with narrowing in the distribution. The critical value of the extent of cell spreading was determined to be 0.54 as a threshold at which a cell is assumed to complete its adhesion to culture surface. The ratio of the number of cells with the extent of cell spreading over 0.54 against the total number of examined cells fairly followed the profile of cell adhesion which was obtained by measuring the number of adherent cells on culture surface. At the cell growth stage in the culture for 20–64 h, doubling time of cell population increased gradually as the culture progressed toward confluence. Generation times (or cell-dividing spans) of individual cells, however, did not show a discriminating dependency on cell concentration and culture time. To clarify the influence of local congestion on the cell division, the generation time was formulated as a function of the number of contact cells around each target cell. Applying the cell placement growth model to estimating the extent of contact inhibition, the reciprocal value of doubling time could be correlated with the average of reciprocal generation times, implying that the doubling time on a cell-population basis is explained by considering the variation in dividing spans of individual cells affected by local contact environment.