The concept of modularity enables parallelization of the design process. Locality: The concept of locality in system ensures that the internal details of each Answer: VLSI Design flow consists of several steps which are carried out in linear . VLSI Design Methodologies EEB (Winter ): Lecture # 4Mani of Structured Design Techniques Hierarchy Regularity Modularity Locality; . architecture structure of accumulator is component reg — definition of. Digital VLSI Circuits. 1. Introduction to ASIC Design a. Design Strategies: Hierarchy, Regularity, Modularity & Locality b. Chip Design Options: Gate Array, Field.
|Published (Last):||18 September 2008|
|PDF File Size:||10.97 Mb|
|ePub File Size:||7.91 Mb|
|Price:||Free* [*Free Regsitration Required]|
A side effect of this complexity hiding is that a sub-module may be changed at any time without disturbing the overall design provided that the changed sub-module continues to support the same interface. The designer attempts to divide the hierarchy into a set of similar blocks.
Hierarchy Rules for Layout
Although top-down design flow provides an excellent design process control, in reality, there is no truly unidirectional top-down design flow. A more detailed view showing the locations of switch matrices used for interconnect routing is given in Fig. Since no physical manufacturing step is modulsrity for customizing the FPGA chip, a functional sample can be obtained almost as soon as the design is mapped into a specific technology.
The design flow starts from the algorithm that describes condept behavior of the target chip. If such improvement is cincept not possible or too costly, then the revision of requirements and its impact analysis must be considered. This is a common format for a black box or abstract layout view provided for an ASIC designer by a cell designer.
Regularity means that the hierarchical decomposition of a large system should result in not only simple, but also similar blocks, as much as possible. Modularity Sub-modules must have well-defined functions and interfaces. Several design styles can be considered for chip implementation of specified algorithms or logic functions.
Regularity usually reduces the number of different modules that need to be regularitj and verified, at all levels of abstraction.
The physical design and layout of logic cells ensure that when cells are placed into rows, their heights are matched and neighboring cells can be abutted side-by-side, which provides natural connections for power and ground lines in each row.
The corresponding architecture of the processor is first defined. While the design implementation of the FPGA chip is done with user programming, that of the gate array is done with metal mask design and processing. The standard cell is also called the polycell. Hierarchy, regularity, modularity vlai locality.
The common specification may include features such as: Modularity in design means that the various functional blocks which make up the larger system must have well-defined functions and interfaces. Wiring should not normally overlap a sub-cell. After routing is completed, the on-chip.
Internal details remain at the local level. The last evolution involves a detailed Boolean description of leaf cells followed by a transistor level implementation of leaf cells and mask generation. For intercell routing, however, some of the uncommitted transistors must be sacrificed.
The concept of modularity enables the parallelisation of the design process. Since the patterning of metallic interconnects is done at the end of the chip fabrication, the turn-around time can be still short, a few days to a few weeks. The failure to properly verify a design in its early phases typically causes significant and expensive re-design at a later stage, which ultimately increases the time-to-market.
The characterization of each cell is done for several different categories. Memory banks RAM cachedata-path units consisting of bit-slice cells, control circuitry mainly consisting of standard cells and PLA blocks.
Design of VLSI Systems – Chapter 1
Connections to Sub-Cells When making connections to any sub-module connections may only be made at defined ports. For most small full custom projects, abstracts are not required since the full details of the leaf cells are available.
The monolithic integration of a large number of functions on a single chip usually provides:. When requirements are not met, the design has to be improved. For timing critical paths, proper gate sizing is often practiced to meet the timing requirements.
The electronics industry has achieved a phenomenal growth over the last two decades, mainly due to the rapid advances in integration technologies, large-scale systems design – in short, due to the advent of VLSI. The third evolution starts with a behavioral module description. If you don’t obey hierarchy rules, a few things may not work but in general you’ll just get a messy, difficult to debug, difficult to explain system.
Regularity Regularity controls the manner in which sub-modules are chosen. While most gate array platforms only contain rows of uncommitted transistors separated by routing channels, some other platforms also offer dedicated memory RAM arrays to allow a higher density where memory functions are required. The magic router also supports the labelling style shown below which uses rectangles for port labels: Here, one can identify four different design styles on one chip: Other than this 0.
Ports By convention, ports in magic are indicated by non-point labels on a particular layer. As a result, the level of actual logic integration tends to fall short of the integration level achievable with the current processing technology. Exceptions to this include the design of high-volume products such as memory chips, high- performance microprocessors and FPGA masters. When comparing the integration density of integrated circuits, a clear distinction must be made between the memory chips and logic chips.
Below are two abstract layouts for NAND gates, illustrating some more complex features: Note that the keep out areas overlap the cell boundary in order to ensure that external Metal1 and Metal2 cannot be placed close enough to the cell to violate spacing rules. Locality By defining well-characterized interfaces for a module, we are stating that any other internal detail is unimportant to any parent module.
In most cases, full utilization of the FPGA chip area is not possible – many cell sites may remain unused. Where modules are well-formed, the interactions with other modules are easy to characterize.
Each design style has its own merits and shortcomings, and thus a proper choice has to be made by designers in order to provide the functionality at low cost.
The actual development of the technology, however, has far exceeded these expectations. Advances in device manufacturing technology, and especially the steady reduction of minimum feature size minimum length of a transistor or an interconnect realizable on chip support this trend. The following figure shows keep out areas for Metal1 and Metal2 for a part of a cell, together with internal elements sufficiently inside the cell boundary.
In this design style, all of the commonly used logic cells are developed, characterized, and stored in a standard cell library.