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@092vk 092vk commented Jun 29, 2025

Fixes #561

Describe the changes you have made in this PR -

  1. Added the logic for pre parameter in the verilog module
  2. According to simulation logic pre is not a control signal but a register which sets the q or output

Note: Please check Allow edits from maintainers. if you would like us to assist in the PR.

Summary by CodeRabbit

  • New Features

    • Asynchronous preset/reset now uses the provided preset vector to initialize outputs.
    • Clock-enable behavior updated so outputs hold their state when enable is inactive.
  • Bug Fixes

    • Fixed initialization so outputs no longer default to fixed zeros/ones on reset.
    • Corrected preset handling to ensure accurate output states across scenarios.

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coderabbitai bot commented Jun 29, 2025

Walkthrough

Verilog generation for the DflipFlop was modified: pre is emitted as a vector alongside d, the asynchronous reset assigns q/q_inv from pre, and clocked updates only change outputs when en is true; hold behavior when en is 0 is explicit.

Changes

Cohort / File(s) Change Summary
DflipFlop Verilog generation
src/simulator/src/sequential/DflipFlop.js
Updated moduleVerilog() to declare input [WIDTH-1:0] d, pre; (removed separate scalar pre), changed async reset to set q/q_inv from pre, and adjusted clocked logic to update q/q_inv only when en is true with explicit hold behavior otherwise.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Assessment against linked issues

Objective Addressed Explanation
Fix errors in Verilog modules of circuit elements, ensuring consistency with simulation logic (#561)
Implement preset (pre) handling in Verilog for flip-flop modules, matching actual logic (#561)
Update Verilog port declarations to match simulation parameters and logic (#561)

(No out-of-scope changes detected.)

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  • src/simulator/src/sequential/DflipFlop.js (1 hunks)
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  • src/simulator/src/sequential/DflipFlop.js
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Actionable comments posted: 0

🧹 Nitpick comments (1)
src/simulator/src/sequential/DflipFlop.js (1)

143-149: Enhanced preset logic aligns well with simulation behavior.

The conditional preset logic correctly implements the behavior where:

  • Unknown preset values result in a safe default state (q=0, q_inv=1)
  • Valid preset values are applied directly to the outputs

This aligns with the JavaScript simulation logic that uses this.preset.value || 0 to handle undefined/null preset values.

Note that the ^pre === 1'bx construct is simulation-specific and may not synthesize. If synthesis compatibility is needed, consider using a different approach for detecting uninitialized signals.

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📥 Commits

Reviewing files that changed from the base of the PR and between 8d8ca00 and c71af00.

📒 Files selected for processing (1)
  • src/simulator/src/sequential/DflipFlop.js (1 hunks)
🧰 Additional context used
🧠 Learnings (2)
📓 Common learnings
Learnt from: 092vk
PR: CircuitVerse/cv-frontend-vue#591
File: v1/src/simulator/src/sequential/JKflipFlop.js:159-188
Timestamp: 2025-06-10T11:26:38.102Z
Learning: In the CircuitVerse project, Verilog modules for circuit elements like JKflipFlop are designed to be consistent with the circuit simulation design, which means reset and preset signals are implemented synchronously (triggered on clock edge) rather than asynchronously, even when the signals are named as asynchronous reset/preset.
src/simulator/src/sequential/DflipFlop.js (2)
Learnt from: 092vk
PR: CircuitVerse/cv-frontend-vue#591
File: v1/src/simulator/src/sequential/JKflipFlop.js:159-188
Timestamp: 2025-06-10T11:26:38.102Z
Learning: In the CircuitVerse project, Verilog modules for circuit elements like JKflipFlop are designed to be consistent with the circuit simulation design, which means reset and preset signals are implemented synchronously (triggered on clock edge) rather than asynchronously, even when the signals are named as asynchronous reset/preset.
Learnt from: 092vk
PR: CircuitVerse/cv-frontend-vue#593
File: v1/src/simulator/src/modules/ALU.js:191-192
Timestamp: 2025-06-10T11:55:53.137Z
Learning: The ALU Verilog module in v1/src/simulator/src/modules/ALU.js currently only supports 1-bit processing. Width parameter support will be added in the future for scalability, even though the JavaScript ALU implementation already supports variable bit widths.
🔇 Additional comments (2)
src/simulator/src/sequential/DflipFlop.js (2)

141-155: Implementation successfully achieves PR objectives.

The Verilog module now correctly treats pre as a vector register that sets the output q, consistent with the circuit simulation logic. Key improvements:

  1. Vector consistency: pre is now a vector input matching the JavaScript preset.bitWidth
  2. Logic alignment: Preset values are applied during reset, consistent with the JavaScript resolve() method (line 65)
  3. Safe defaults: Unknown preset values are handled gracefully

This aligns with the retrieved learning about CircuitVerse's synchronous reset/preset implementation approach.


138-139: Confirm Port Ordering Impact on DflipFlop Instantiations

The change making pre a vector input correctly aligns the Verilog with the JavaScript simulation logic. However, it does alter the port ordering:

• File: src/simulator/src/sequential/DflipFlop.js
Lines 138–139:

    input clk, a_rst, en;
    input [WIDTH-1:0] d, pre;

Please verify that every instantiation of this module now uses named port connections (rather than positional) to avoid mismatches.

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lgtm

@niladrix719 niladrix719 requested a review from JoshVarga July 4, 2025 18:34
@niladrix719 niladrix719 merged commit 8757281 into CircuitVerse:main Aug 24, 2025
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Fix the errors in the Verilog module of the circuit elements
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