Load-Word Instruction Model
The Load-Word Instruction Model is an example instruction model used in the Genesys-Pro test-generation framework to describe a processor instruction as a constraint problem over operands, attributes, and architectural relations. In the cited model, a Load-Word instruction loads four bytes from memory into a general-purpose register.[1]
Context
Genesys-Pro uses a model-based approach in which architecture-specific knowledge is separated from the test-generation engine.[2] This separation lets users maintain models for multiple designs and adapt to ongoing design changes without depending directly on tool developers.[1]
In Genesys-Pro, instructions form the bulk of the processor model and are described as constraint problems consisting of attributes and relations.[2] Instruction attributes can include an opcode and resource-related attributes such as data, resource family, address, and number of units.[1]
Structure of the Model
The Load-Word model is organized as a tree of operands. Attribute names and value domains are associated with nodes in the tree.[1]
Top-Level Instruction
The model represents a Load-Word instruction with two main operands:
| Operand | Role |
|---|---|
source |
Memory operand from which four bytes are loaded |
target |
General-purpose register receiving the loaded data |
The instruction is described as loading four bytes from memory.[1]
Source Memory Operand
The source operand belongs to the memory resource family and has:
- an address domain shown as
[0:2^32 − 1]; Units = 4, corresponding to four bytes;- a data domain shown as
[0:2^32 − 1].[2]
The source memory operand has two sub-operands:
base, a general-purpose register;displacement, an immediate field.[1]
Base Register Operand
The base operand is modeled as a general-purpose register with:
- address domain
[0:31]; Units = 1;- data domain
[0:2^32 − 1].[2]
Displacement Operand
The displacement operand is modeled as an immediate data field with a value domain shown as [0:2^16 − 1].[2]
Target Register Operand
The target operand is a general-purpose register with:
- address domain
[0:31]; Units = 1;- data domain
[0:2^32 − 1].[2]
Constraints and Relations
In the Load-Word model, arcs between attributes represent relations, and these relations correspond to constraints imposed by the architectural definition of the instruction.[1]
A key address-generation constraint is:
source.address = base.data + displacement.data
This relation states that the memory address used by the Load-Word instruction is computed as the sum of the contents of the base register and the displacement field.[1]
The model also includes a constraint preventing the base register and target register from being the same architectural register:
base.address ≠ target.address
This constraint appears in the Load-Word instruction model diagram.[2]
Representation in Genesys-Pro
Genesys-Pro represents instruction relations directly in the model when they can be expressed as equations using arithmetic and Boolean operators.[1] For relations with more complex semantics, the model can refer to an external C++ implementation supplied by the modeling engineer.[1]
The Load-Word example illustrates the framework’s constraint-based representation of instruction components. Such representation is intended to provide flexibility for modeling different and complex processor architectures.[1]
Role in Test Generation
The instruction model contributes to Genesys-Pro’s hybrid test-generation approach, in which instruction-level generation uses constraint satisfaction techniques.[1] This approach supports generation of long tests, potentially tens of thousands of instructions, increasing the chance of reaching verification events such as filling large buffers or exploring machine states that require nontrivial execution paths.[1]
Summary
The Load-Word Instruction Model is a constraint-based description of a memory-to-register load instruction in Genesys-Pro. It models the instruction as a tree of operands—source memory, target register, base register, and displacement—and defines architectural relations such as effective-address calculation and register inequality constraints. This example demonstrates how Genesys-Pro separates architecture-specific instruction knowledge from the generation engine while allowing executable constraints to drive instruction-level test generation.