Loading Waveform Files

NovyWave supports loading multiple waveform files simultaneously, making it easy to correlate signals from different simulations or design partitions.

Supported Formats

Format	Extension	Description	File Size	Parse Speed
VCD	.vcd	Value Change Dump — IEEE standard, ASCII, human-readable	Large	Slow
FST	.fst	Fast Signal Trace — binary, compressed, random access	Small (10-100x less than VCD)	Fast
GHW	.ghw	GHDL Waveform — binary, full VHDL type support	Medium	Medium

Recommendations:

• Use FST for Verilator projects (best performance)
• Use GHW for GHDL/VHDL projects
• Use VCD for maximum compatibility or debugging

Loading Files

Using the File Dialog

1. Click Load Files in the Files & Scopes panel header
2. Navigate to your waveform files
3. Select one or more files (use Ctrl/Cmd+click for multiple selection)
4. Click Load or press Enter

Drag and Drop

Drag waveform files from your file manager directly onto the NovyWave window.

Working with Loaded Files

File Tree Structure

Loaded files appear in the Files & Scopes panel as a tree:

design.vcd (0-100ns)
  └── TOP
      ├── cpu
      │   └── alu
      └── memory

Each file shows:

• File name (with disambiguation path if needed)
• Time span (e.g., 0-100ns)
• Expandable hierarchy of modules/scopes

Selecting Scopes

Click the checkbox next to a scope to select it. The Variables panel shows signals from the selected scope.

Expanding/Collapsing

• Click the chevron to expand or collapse a scope
• Expansion state is preserved between sessions

Removing Files

• Click the X button on a file row to remove it
• Use Remove All in the header to clear all files

File Disambiguation

When loading files with the same name from different directories, NovyWave adds path prefixes:

project/module_a/test.vcd  →  module_a/test.vcd
project/module_b/test.vcd  →  module_b/test.vcd

Creating Waveform Files

VCD from Verilog (Icarus Verilog)

initial begin
    $dumpfile("output.vcd");
    $dumpvars(0, top_module);
end

FST from Verilator

Verilated::traceEverOn(true);
VerilatedFstC* tfp = new VerilatedFstC;
top->trace(tfp, 99);
tfp->open("output.fst");

GHW from GHDL

ghdl -r testbench --wave=output.ghw

Converting VCD to FST

vcd2fst input.vcd output.fst

Multi-File Workflows

NovyWave excels at working with multiple waveform files simultaneously.

Loading Multiple Files

• Multi-select in the file dialog (Ctrl/Cmd+click)
• Sequential loading — click Load Files again to add more files
• Drag and drop multiple files at once

Time Alignment

Most simulations start at time 0, so multiple files naturally align. When files have different durations, the timeline extends to cover the longest file. Signals show “N/A” outside their file’s time range.

Selecting Variables Across Files

Variables from different files appear together in the waveform view:

1. Select scope from File A, add signals
2. Select scope from File B, add signals
3. All signals display on the same timeline

Each variable shows its full path for identification:

design.vcd|TOP|cpu|clk
memory.vcd|TOP|mem|clk

NovyWave remembers your multi-file setup — loaded files, selected scopes, selected variables, and expansion states are all persisted.

Troubleshooting

File Won’t Load

• Check the file format is supported (VCD, FST, GHW)
• Ensure the file isn’t corrupted or truncated
• Check file permissions

Slow Loading

Large files (>100MB) may take a few seconds to parse. Consider using FST format instead of VCD for 10-100x smaller files and faster loading.

Missing Signals

• Expand the file tree to find scopes
• Use the search box in Variables panel to filter
• Check that the correct scope is selected