Architectural Variable (AV)

Concept

An Architectural Variable (AV) is a state variable of a hardware module (processor or accelerator) as modeled within an Instruction-Level Abstraction (ILA). AVs are the named, abstract state elements whose values define the observable architectural state of a design, and they are the units of equivalence that are checked (AV-Check) and transferred (AV-Swap) between a high-level Instruction-Level Execution Model (ILEM) and an RTL-based Execution Model (RTEM) during tandem simulation.

First seen 6/6/2026

Last seen 6/6/2026

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Overview

An Architectural Variable (AV) is a state variable in an Instruction-Level Abstraction (ILA) that captures the abstract, observable state of a processor or accelerator at the instruction level. AVs generalize the notion of architectural state — historically tied to processor ISAs — to hardware accelerators and other SoC components, enabling uniform instruction-level modeling and verification across heterogeneous designs.

In an ILA, a design is described by:

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RELATIONSHIPS

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Tandem Simulation ← uses 98% 2e

Tandem simulation checks and swaps architectural variables

Instruction-Level Abstraction (ILA) part of → 97% 1e

ILA specifies a set of architectural variables

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Tandem Simulation USES Extracted graph relationship

Instruction-Level Abstraction (ILA) PART_OF Extracted graph relationship

CITATIONS

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7 citations — click to expand

[1] An ILA model is defined as a tuple ⟨S, W, S0, D, N⟩, where S is the set of architectural variables (AVs) and W is the set of inputs. Generalizing Tandem Simulation: Connecting High-level and RTL Simulation Models

[2] The ISA can be viewed as a special case of an ILA, and the ILA for accelerators specifies a set of instructions and AVs. Generalizing Tandem Simulation: Connecting High-level and RTL Simulation Models

[3] In the AES accelerator example, the AVs include the encryption key, text length, address, status, data_mem, and output_data, while the inputs are MMIO interface signals such as addr_in, data_in, and cmd. Generalizing Tandem Simulation: Connecting High-level and RTL Simulation Models

[4] The state update function N is a state transition function for the architectural variables, which lends itself to direct translation to an ILEM for co-simulation. Generalizing Tandem Simulation: Connecting High-level and RTL Simulation Models

[5] Tandem simulation performs AV-Check at the end of each instruction (or at checkpoints) to verify that ILAVs and RTAVs are equivalent. Generalizing Tandem Simulation: Connecting High-level and RTL Simulation Models

[6] Tandem simulation supports AV-Swap, transferring values of AVs from the ILEM to the RTEM to jump-start the RTL simulation and reduce warm-up time. Generalizing Tandem Simulation: Connecting High-level and RTL Simulation Models

[7] ILAs support hierarchy through child-ILAs, enabling complex instructions (e.g., START_ENCRYPT) to be decomposed into child-instructions. Generalizing Tandem Simulation: Connecting High-level and RTL Simulation Models