Verilog作业求助：如何在RTL原理图中显示Demux模块

Let’s walk through the most common reasons your Demux isn’t showing up in the schematic, along with actionable fixes:

1. Double-Check Demux Instantiation in top_module #

First, confirm you’ve properly instantiated the Demux in your top-level code—small typos or missing connections are often the culprit:

• Ensure the module name in the instantiation exactly matches your Demux’s definition (Verilog is case-sensitive in most tools).
• Verify all critical ports are connected to valid signals: for your use case, this should include a select signal (to switch between counter and priority encoder outputs), inputs from both the counter and priority encoder, and an output feeding into the s1 register.

Example of a correct instantiation (adjust to your module’s port names):

demux your_demux_inst (
    .select(multiple_interrupt_flag), // Signal indicating multiple interrupts
    .input_counter(counter_out),      // Output from the counter module
    .input_priority(prio_encoder_out),// Output from the priority encoder
    .output_s1(s1_reg)                // Connected directly to your s1 register
);

2. Check for Synthesis Optimization Removal #

Synthesis tools automatically eliminate modules that don’t contribute to the final circuit’s outputs. Your Demux might be getting optimized out if:

• Its output isn’t connected to s1 (or a signal that feeds into s1).
• The select signal is tied to a constant value (e.g., 1'b0), making the Demux redundant—tools will replace it with just the selected input.
• The Demux has unused inputs/outputs that don’t affect the circuit’s behavior.

Check your synthesis log for warnings like "Unused module" or "Signal not driving any load"—these are clear clues the Demux is being removed.

3. Adjust Synthesis Tool Hierarchy Settings #

Many tools default to flattening hierarchical modules, which can hide individual submodules like your Demux:

• Look for settings like "Preserve Hierarchy" or "Flatten Hierarchy" in your synthesis tool (e.g., Vivado, Quartus). Set it to Preserve Hierarchy to keep submodules visible.
• In tools like Vivado, you can add an attribute to your top_module to force hierarchy preservation:

  (* keep_hierarchy = "yes" *) module top_module(...);
  

4. Validate Demux Module Definition & Project Inclusion #

• Ensure your Demux module has no syntax errors (missing semicolons, mismatched port directions, etc.).
• Confirm the Demux file is actually added to your project’s source list in the synthesis tool—sometimes files are written but not included in the build.

5. Isolate with a Minimal Test #

If you’re still stuck, create a stripped-down version of top_module that only includes the Demux, counter, priority encoder, and s1 register. This will help you rule out complex interactions in your full design causing the issue.

After addressing these points, re-run synthesis and refresh your RTL schematic—your Demux should appear if connections and settings are correct!

内容的提问来源于stack exchange，提问作者Murat Tekin