Uncategorized

Logical Gate Level

At the Logical Gate Level the design is represented by a netlist that uses only cells from a small number of single-bit cells, such as basic logic gates (AND, OR, NOT, XOR, etc.) and registers (usually D-Type Flip-flops). A number of netlist formats exists that can be used on this level such as the Electronic Design Interchange Format (EDIF), but for ease of simulation often a HDL netlist is used. The latter is a HDL file (Verilog or VHDL) that only uses the most basic language constructs for instantiation and connecting of cells.

Physical Gate Level

On the Physical Gate Level only gates are used that are physically available on the target architecture. In some cases this may only be NAND, NOR and NOT gates as well as D-Type registers. In the case of an FPGA-based design the Physical Gate Level representation is a netlist of LUTs with optional output registers, as these are the basic building blocks of FPGA logic cells.

Switch Level

A Switch Level representation of a circuit is a netlist utilizing single transistors as cells. Switch Level modeling is possible in Verilog and VHDL, but is seldom used in modern designs, as in modern digital ASIC or FPGA flows the physical gates are considered the atomic build blocks of the logic circuit.

⦁ Planning Switch Level Hardware

A Floor-Planner of an Integrated Circuit (IC) is a schematic representation of tentative placement of its major functional blocks. In modern electronic design process floor-plans are created during the floor-planning design stage, an early stage in the hierarchical approach to Integrated Circuit design. Depending on the design methodology being followed, the actual definition of a floor-plan may differ.

⦁ Placing Switch Level Hardware

A Standard Cell Placer takes a given synthesized circuit netlist together with a technology library and produces a valid placement layout. The layout is optimized according to the aforementioned objectives and ready for cell resizing and buffering, a step essential for timing and signal integrity satisfaction. Physical design flow are iterated a number of times until design closure is achieved.

⦁ Timing Switch Level Hardware

A Standard Cell Timing-Analizer is a simulation method of computing the expected timing of a digital circuit without requiring a simulation of the full circuit. High-performance integrated circuits have traditionally been characterized by the clock frequency at which they operate. Measuring the ability of a circuit to operate at the specified speed requires an ability to measure, during the design process, its delay at numerous steps.

⦁ Routing Switch Level Hardware

A Standard Cell Router takes pre-existing polygons consisting of pins on cells, and pre-existing wiring called pre-routes. Each of these polygons are associated with a net. The primary task of the router is to create geometries such that all terminals assigned to the same net are connected, no terminals assigned to different nets are connected, and all design rules are obeyed.

⦁ Simulating Switch Level Hardware

A Standard Cell Simulator 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. This simulator represents a circuit in terms of its exact transistor structure but describes the electrical behavior in a highly idealized way.

⦁ Verifying Switch Level Hardware

A Standard Cell Verifier compares netlists, a process known as LVS (Layout vs. Schematic). This step ensures that the geometry that has been laid out matches the expected circuit. The greatest need for LVS is in large analog or mixed-signal circuits that cannot be simulated in reasonable time. LVS can be done faster than simulation, and provides feedback that makes it easier to find errors.

⦁ Checking Switch Level Hardware

A Standard Cell Checker is a geometric constraint imposed on Printed Circuit Board (PCB) and Integrated Circuit (IC) designers to ensure their designs function properly, reliably, and can be produced with acceptable yield. Design Rules for production are developed by hardware engineers based on the capability of their processes to realize design intent. Design Rule Checking (DRC) is used to ensure that designers do not violate design rules.

⦁ Printing Switch Level Hardware

A Standard Cell Editor allows to print a set of standard cells. The standard cell methodology is an abstraction, whereby a low-level VLSI layout is encapsulated into a logical representation. A standard cell is a group of transistor and interconnect structures that provides a boolean logic function (AND, OR, XOR, XNOR, inverters) or a storage function (flipflop or latch).

References:
http://opencircuitdesign.com/
http://www.clifford.at/yosys/

Behavioral Level (Structural Description) entity

At the Behavioural Level abstraction a language aimed at hardware description such as Verilog or VHDL is used to describe the circuit, but so-called behavioural modeling is used in at least part of the circuit description. In behavioural modeling there must be a language feature that allows for imperative programming to be used to describe data paths and registers. This is the always -block in Verilog and the process -block in VHDL.

Register Transfer Level (Functional Description) architecture

A design in Register Transfer Level representation is usually stored using HDLs like Verilog and VHDL. But only a very limited subset of features is used, namely minimalistic always blocks (Verilog) or process blocks (VHDL) that model the register type used and unconditional assignments for the datapath logic. The use of HDLs on this level simplifies simulation as no additional tools are required to simulate a design in Register Transfer Level representation.

⦁ Describing Register Transfer Level Hardware

A Hardware Description Language Editor is any editor that allows to generate hardware code. Hardware Description Language is a specialized computer language used to describe the structure and behavior of digital logic circuits. It allows for the synthesis of a HDL into a netlist, which can then be synthesized, placed and routed to produce the set of masks used to create an integrated circuit.

⦁ Simulating Register Transfer Level Hardware

A Hardware Description Language Simulator uses mathematical models to replicate the behavior of an actual hardware device. Simulation software allows for modeling of circuit operation and is an invaluable analysis tool. Simulating a circuit’s behavior before actually building it can greatly improve design efficiency by making faulty designs known as such, and providing insight into the behavior of electronics circuit designs.

⦁ Synthesizing Register Transfer Level Hardware

A Hardware Description Language Synthesizer turns a RTL implementation into a Logical Gate Level implementation. Logical design is a step in the standard design cycle in which the functional design of an electronic circuit is converted into the representation which captures logic operations, arithmetic operations, control flow, etc. In EDA parts of the logical design is automated using synthesis tools based on the behavioral description of the circuit.

⦁ Optimizing Register Transfer Level Hardware

A Hardware Description Language Optimizer finds an equivalent representation of the specified logic circuit under specified constraints (minimum area, pre-specified delay). This tool combines scalable logic optimization based on And-Inverter Graphs (AIGs), optimal-delay DAG-based technology mapping for look-up tables and standard cells, and innovative algorithms for sequential synthesis and verification.

⦁ Verifying Register Transfer Level Hardware

A Hardware Description Language Verifier proves or disproves the correctness of intended algorithms underlying a hardware system with respect to a certain formal specification or property, using formal methods of mathematics. Formal verification uses modern techniques (SAT/SMT solvers, BDDs, etc.) to prove correctness by essentially doing an exhaustive search through the entire possible input space (formal proof).

System Level (Hierarchical Description)

The System Level abstraction of a system only looks at its biggest building blocks like processing units or peripheral devices. At this level the circuit is usually described using traditional programming languages like SystemC or SystemVerilog. Sometimes special software libraries are used that are aimed at simulation circuits on the system level. The IEEE 1685-2009 standard defines the IP-XACT file format that can be used to represent designs on the system level and building blocks that can be used in such system level designs.

⦁ Modeling System Level Hardware

A System Design Language Editor is any editor that allows to generate software code. A System Design Language is a formal language, which comprises a Programming Language (input), producing a Hardware Description (output). Programming languages are used in computer programming to implement algorithms. The description of a programming language is split into the two components of syntax (form) and semantics (meaning).

System Level (Hierarchical Description)
The System Level abstraction of a system only looks at its biggest building blocks like processing units or peripheral devices. At this level the circuit is usually described using traditional programming languages like SystemC or SystemVerilog. Sometimes special software libraries are used that are aimed at simulation circuits on the system level. The IEEE 1685-2009 standard defines the IP-XACT file format that can be used to represent designs on the system level and building blocks that can be used in such system level designs.

⦁ Modeling System Level Hardware

A System Design Language Editor is any editor that allows to generate software code. A System Design Language is a formal language, which comprises a Programming Language (input), producing a Hardware Description (output). Programming languages are used in computer programming to implement algorithms. The description of a programming language is split into the two components of syntax (form) and semantics (meaning).

⦁ Simulating System Level Hardware

A System Description Language Simulator (translator) is a computer program that translates computer code written in a Programming Language (the source language) into a Hardware Design Language (the target language). The compiler is primarily used for programs that translate source code from a high-level programming language to a low-level language to create an executable program.

⦁ Verifying System Level Hardware

A UVM standard improves interoperability and reduces the cost of repurchasing and rewriting IP for each new project or Electronic Design Automation tool. It also makes it easier to reuse verification components. The UVM Class Library provides generic utilities, such as component hierarchy, Transaction Library Model or configuration database, which enable the user to create virtually any structure wanted for the testbench.