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Q148FreeDesign Verification

Direct Programming Interface (DPI) 4-state data mapping

Difficulty
Medium
Topic
Verification Utilities
Language
SV
Interview prompt

Question

A C model must distinguish 0, 1, X, and Z for every bit of a 32-bit bus. Which SystemVerilog Direct Programming Interface (DPI) boundary choice preserves that information?

Provided context

Code to inspect

// SystemVerilog declaration
import "DPI-C" function void inspect_bus(
  input logic [31:0] bus
);

// Matching C declaration from svdpi.h
// void inspect_bus(const svLogicVecVal* bus);
Choose one

Answer choices

  1. A. Use bit [31:0] and an svBitVecVal representation; X and Z are preserved
  2. B. Use logic [31:0] and an svLogicVecVal representation carrying value and unknown-state information
  3. C. Use int unsigned; all four states are encoded automatically in its numeric value
  4. D. Use real and reinterpret its mantissa as four-state bits
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