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The book includes real-world examples of formal verification applied to complex design Formal Verification, ASAP Applied Formal Verification delivers right-now methods for integrating this powerful tool into your design process. Get A Copy. Kindle Edition , pages. More Details Friend Reviews. To see what your friends thought of this book, please sign up. To ask other readers questions about Applied Formal Verification , please sign up.
Be the first to ask a question about Applied Formal Verification. Ricky W. Cyrluk and P. Cyrluck, S. Rajan, N. Shankar, and M. Ben L. Di Vito, Ricky W. Butler, and James L. SE, No. Gerhart, M. Bouler, K. Greene, D. Jamsek, T.
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Melham Eds. Warren A. Cliff B. Ramayya Kumar and Thomas Kropf Eds. Mandayam Srivas et al. In another embodiment, the abstraction tool detects a datapath circuit in a circuit design by detecting a specific datapath library component instantiated in an RTL model of the design. This technique may be used as an alternative to directly detecting datapath structures coded in a synthesizable register-transfer-level RTL description, or it may be used in addition to the structural analysis techniques.
Applied Formal Verification
Using libraries of components allows the abstraction tool to detect datapath components in a circuit design more reliably and with relatively fewer resources, so this technique can be substantially less demanding than a structural analysis of the circuit design. To use library components in the design, the user selects a pre-coded datapath component from a component library of datapath models.
This pre-coded model is instantiated into either the user's circuit design e. This enables the user to quickly develop code that has a particular datapath behavior in the model. The instantiated datapath component contains all the details for the user to simulate the datapath behavior when instantiated in the design. Detection of the instantiated components is easy because the abstraction tool may simply match components in the circuit design against the known datapath components from the component library In one embodiment, the component library contains the functional details for the desired datapath component, but not the abstraction for it.
Accordingly, when a user instantiates a datapath component into the design, the datapath functionality but not the abstraction model is included in the design. After the design is passed to the formal verification system , the datapath abstraction tool detects library components in the design and automatically replaces the datapath components with an abstraction model optimized for the formal verification system The abstraction models for the detected datapath components may be obtained from an abstraction component library that is internal to the formal verification system These abstraction models may be valuable intellectual property, so this scheme helps to maintain these models as proprietary information.
Because library components are used, in one embodiment, the user needs only an understanding of the design and not of the formal verification or abstraction processes. The abstraction tool can thus accelerate formal verification engines without requiring the user to learn the technical details of formal verification or abstraction. Effectiveness and ease of use are thus enhanced by automating the application of the abstraction. Non-experts in formal verification can verify a design without learning algorithmic or abstraction techniques in formal verification.
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During the interaction with the tool, they are only given choices related to their designs, and not on choices about specific abstraction techniques. This allows the abstraction tool to be used by a wider range of professionals. Once a datapath circuit is detected in a circuit design, the abstraction tool replaces the detected datapath circuit with a simpler abstraction model optimized for the functional formal verification process.
Datapaths include a number of data signals and state-elements that have no functional significance to the property to be verified, so the resulting states that have no functional significance can be abstracted. Regardless of whether the user chooses to directly code the behavior of the datapath in the RTL description or whether the user chooses to instantiate a datapath component from a library of pre-coded components into their design or requirements model, the user does not have to understand the details of the datapath abstraction that are required for efficient functional formal verification.
Once the datapath circuit has been detected, the tool automatically replaces the datapath circuit with an abstraction model of the datapath. This replacement technique is automatically performed in the functional formal verification tool and thus does not require modification to the user's original RTL description. In this way, an expert in datapath abstraction techniques or functional formal verification is no longer required, which overcomes one of the factors currently limiting the adoption of functional formal verification in an industrial setting.
This abstraction takes advantage of the observation that only three unique data item values are sufficient to verify that the design will not drop, duplicate, or corrupt any data items as they pass through the portion of the design containing the datapath circuit that is, as the data pass from the input of the datapath element to the output of the datapath element. Furthermore, the abstraction takes advantage of the symmetry involved in the datapath circuits to reduce the width of a wide datapath circuit down to a very narrow width.
In general, only a single bit is required to prove data integrity and correct ordering for message or packets of equal priority, as demonstrated by C. Stangier and U. However, for designs where arriving messages or packets are assigned various priorities, additional bits may be required for the abstraction. For designs containing two priority levels for arriving messages or packets, for example, two bits are required for the abstraction to handle the two classes of priority. In one example, two bits i, j are arbitrarily selected from a wide datapath circuit, resulting in a narrow two-bit width datapath.
For example, consider an n-bit wide datapath:. Hence, the reduced data item is modeled as follows using Verilog for this example :. The arbitrarily selected two bits from the n-bit wide data item are concatenated together to form a narrow two-bit data item. Other encodings of the reduced two-bit data item are possible. The abstraction model illustrated in FIG. In one embodiment, the abstraction shown in FIG. The actual datapath description in the original code is ignored by the tool, while the abstraction is incorporated into the formal verification as a set of assumptions.
This embodiment of the invention enables abstraction without direct manipulation of the RTL description. This abstraction can be introduced as an assumption in a formal verification tool. For the output of the memory from which data are sent out, the following assumptions can be used:. This datapath abstraction permits the formal verification tool to prove the following class of properties: If a packet P 2 is of higher or equal priority as a packet P 1 , then if P 2 arrives before P 1 , then P 2 must exit the design before P 1.
The priority of packet is encoded in the reduced two-bit narrow width datapath abstraction. If a design supports multiple priority levels, it can be proved that only three bits are required to encode the various priority levels. Similarly, for a design that supports only a single priority of input packets, only a single bit is required for the abstraction.
This abstraction eliminates the need to model a memory store or array of registers, thus reducing the number of states required to perform the formal verification proof on the circuit design.
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In one embodiment, the datapath abstraction tool is configured to use the identification of a datapath circuit to deduce additional datapath circuits, for which an abstraction can be applied. Deducing datapaths from known datapaths in a circuit design takes advantage of the observation that datapath elements commonly drive other datapath elements in a circuit. In such cases, the data entering a block in a design will often encounter a series of datapath elements before it exist the block.
In one example of abstracting the design, the datapath abstraction tool detects the presence of the FIFO in the circuit design To deduce additional datapath elements, the abstraction tool traces the data signal backward from the input of the detected FIFO towards the input of the design. As this tracing occurs, the path may branch, and the tool may follow one or more of the paths that are likely to contain datapath elements.
In the example shown in FIG. As the tool traces backward in the design , it attempts to determine whether the encountered components are datapath elements that should be abstracted. To determine whether a component is a datapath element, the tool may use any of the techniques described above, including structural analysis, library component identification, user input, and any combination thereof. If the tool determines that a component is a datapath element that should be abstracted, the tool replaces that element with an appropriate abstraction or marks the element for abstraction later.
Once the tool reaches the input, the tool traces forward from the input, branching as necessary and as desired. When this FIFO is encountered, the tool determines that FIFO is indeed a datapath element, and performs an appropriate abstraction on it as described above.
Any other datapath elements in the circuit design and in the requirements model can likewise be identified and abstracted. When tracing along a data signals, it is expected that the tool will generally encounter elements such as multiplexers, demultiplexers, buffers, inverters, and similar components. If the tool encounters other types of logic, such as logic that performs a transformation or computation on the traced signal, it is less likely that the traced path will lead to the types of datapath elements that can be abstracted in accordance with embodiments of the invention.
Accordingly, in one embodiment, the tool halts tracing on a particular path if it encounters such logic or other types of components that indicate that the path probably does not contain datapath elements. Although tracing backward and then forward is described, the tool may deduce additional abstractions by traversing any desired route in the circuit design and model.
In various embodiments, one or more tracing routes may begin from an identified datapath element or data signal or from a location provided by the user. By deducing datapaths, the tool can reduce the set of possible candidates for datapath identification, which lessens the computational burdens on the tool. For example, while it may be relatively simple to identify a datapath element if the user instantiates one from a library of datapath models, identifying datapaths using the structural analysis detection scheme may be costly.
Hence, once a datapath is identified, the work of identifying other datapath elements can be reducing using a tracing technique to deduce other datapaths, which is less costly. In another embodiment, the datapath abstraction tool is configured to link one or more identified abstracted datapath elements to an input of the circuit design Taking an example to illustrate how the abstraction is linked, the FIFO is abstracted with the following set of assumptions:.
These assumptions affect the inputs to the FIFO ; however, the assumptions created for the FIFO can be linked so that they also influence the input signal of the design block In other words, the two bits that are set to the tagged value by the assumption will apply to the same two bits propagated through the design from the input.
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As the signal is propagated backward, it is passed through various buffering elements, such as multiplexers and registers. In the example provided, the set of assumptions become:. In this way, the abstraction modeled for the FIFO is related to the input signal for the design so that, ultimately, the same two bits tagged at the FIFO input will be set the same way at the input when the constraint is propagated backward.
In one embodiment, however, if propagating the signal would require passing through data transforming elements, there is no need to propagate the abstraction backward because the datapath is not likely to be of the type abstracted in accordance with an embodiment of the invention. Accordingly, if the tool encounters such elements in the path, the tool does not perform linking of the abstraction.
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