Hydra Sim Student — FREE Verilog Simulator

A VS Code extension for running, visualizing, replaying, Verilog simulations — step-by-step, directly inside the editor. A future version will support Agentic AI analyzer to support intent based debug and verification.

Features

• Run Simulation — Execute the open Verilog file through the Hydra simulator with a single shortcut.
• Step-by-Step Replay — Navigate forward and backward through simulation timeline frames, one event queue step at a time.
• Color-Coded Queue Highlights — Lines are highlighted by event queue membership (Active, Inactive, NBA, Monitor, Future) at every step.
• Inline Signal Annotations — Signal values and simulation time are annotated inline, next to their declaration lines.
• Live Waveform Viewer — A canvas-based waveform panel opens in a new window, updating automatically as you step.
• Frozen Waveform Comparison — Re-running the simulation freezes the previous waveform panel in place so you can compare runs side by side.
• Legend Overlay — A floating color legend stays pinned to the bottom of the viewport while simulation is active.
• AI RTL Assistant — A chat panel that can answer questions about your design, detect waveform patterns to ensure compliance/non-compliance against user provided data sheets on protocols or IPs used.
• Compile Workspace — Compile all .v files specified through the source YAML variable in hydra.yaml that defines the workspace through the Hydra simulator for module-lookup and syntax checking.
• Hierarchy Browser - The viewer to show the Hierarchical Structure of the design with ability to control which waveforms to be shown in the waveform viewer.
• Verilog 2001 - Hydra Sim supports Verilog 2001 with the
• exception of the following constructs
• |-forever
• |-repeat
• |-cazex/casez
• |-generate for
• |-generate if
• |-mixed signed arithmetic
• |-replication
• |-dumpvar
• |-dumpfile
• |-pointer arithmetic

Getting Started

1. Open a .v Verilog file in VS Code.
2. Press Compile Workspace (see keybindings below) or click the Hydra icon on the left primary sidebar to show up the hierarchy browser and click on "Compile workspace" button.
3. Press Run Simulation (see keybindings below) or click on play icon in the top right corner of the file window.
4. The waveform panel opens automatically in a new window.
5. Use Step Forward / Step Backward to navigate the timeline.
6. Press Exit Replay to clear all highlights and reset state.
7. Press Open RTL Assistant to start the AI chat panel (will be functional in 1.1.0).

Commands & Keybindings

Linux note: Simulation commands use function keys to avoid conflicts with Ctrl+Alt / AltGr key combinations common on Linux desktop environments.

All commands are also available via the Command Palette (Ctrl+Shift+P). Simulation keybindings require editor focus (editorTextFocus).

You can rebind any command via File → Preferences → Keyboard Shortcuts.

Editor Decorations

At each simulation step, lines in the active editor are highlighted by their event queue:

Additional inline annotations appear automatically:

• Simulation time — shown once below the module header line (// Simulation Time = N).
• Signal values — current 0/1 value shown next to each signal declaration (// Value=0).
• When / Current markers — each queued line annotated with its scheduled time (// When=N).

Waveform Viewer

Running a simulation opens a Hydra Live Waveform panel in a separate VS Code window. The panel:

• Updates automatically as you step forward or backward.
• Is retained when hidden — navigating away and back does not require a reload.
• Is frozen in place (title changes to "Hydra Waveform (Frozen)") when you re-run the simulation, so you can compare the old and new runs side by side.
• Plots all accumulated signal transitions over the full simulation time axis.

Workflow Overview

Open .v file
     ↓
Run Simulation  ──────────────────────────────────────────────────┐
     ↓                                                            │
Waveform panel opens (new window)                        Re-run freezes old panel
     ↓
First frame applied → editor decorations + inline annotations
     ↓
Step Forward / Step Backward  ←──────────────────────────────────-┐
     ↓                                                            │
Editor decorations update + waveform updates                      │
     ↓                                                            │
Exit Replay → decorations cleared, legend hidden, waveform closed─┘

License

See the repository root for license information.