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solomatnikov opened this issue Jul 15, 2024 · 5 comments
Open

Support unassigned virtual interfaces #5265

solomatnikov opened this issue Jul 15, 2024 · 5 comments
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status: ready Issue is ready for someone to fix; then goes to 'status: assigned' type: feature-IEEE Request to add new feature, described in IEEE 1800

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@solomatnikov
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%Error-UNSUPPORTED: test2.sv:740:12: Unsupported: virtual interface never assigned any actual interface
  740 |    virtual z_driver_if vif;
      |            ^~~~~~~~~~~
                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=5.027
%Error-UNSUPPORTED: test2.sv:741:25: Unsupported: virtual interface never assigned any actual interface
  741 |    function new(virtual z_driver_if _vif);
      |                         ^~~~~~~~~~~
%Error: Exiting due to 2 error(s)
        ... See the manual at https://verilator.org/verilator_doc.html for more assistance.

VCS compiles without errors.

Can you attach an example that shows the issue? (Must be openly licensed, ideally in test_regress format.)

class z_bfm;  
   virtual z_driver_if vif;
   function new(virtual z_driver_if _vif);
      vif = _vif;
   endfunction  
   virtual function void init;
   endfunction  
endclass
module test_cw;
  (
   input  logic     clk,
   input  logic     reset_l,
   z_if.sender    z,
                    mmio_z
   );
   z_driver_if    mem_z_drv(clk, z),
                    mmio_z_drv(clk, mmio_z);
   z_bfm mem_z_bfm,
           mmio_z_bfm;
   initial begin
      mem_z_bfm  = new(mem_z_drv);
      mmio_z_bfm = new(mmio_z_drv);
      mem_z_bfm.init;
      mmio_z_bfm.init;
   end
endmodule

test_cw is never used/instantiated.

What 'verilator' command line do we use to run your example?

verilator -Wno-LATCH -Wno-STMTDLY -Wno-WIDTH -Wno-UNUSED --cc --exe -sv --assert --trace --trace-params --trace-structs --report-unoptflat --no-timing --timescale 1ps/1ps --x-assign unique -fno-const-bit-op-tree -fno-dfg-peephole -Wno-SYMRSVDWORD --top-module top test2.sv

What 'verilator --version' are you using? Did you try it with the git master version?

v5.026-g34e37d7bd

What OS and distribution are you using?

Linux 5.14.0-427.24.1.el9_4.x86_64
@solomatnikov solomatnikov added the new New issue not seen by maintainers label Jul 15, 2024
@sterin
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sterin commented Jul 22, 2024

Simpler examples:

interface I;
endinterface

class C;  
   virtual I vi;
endclass

module top;
endmodule

results in

%Error-UNSUPPORTED: bug.sv:5:12: Unsupported: virtual interface never assigned any actual interface
    5 |    virtual I vi;
      |            ^

and

interface I;
endinterface

class C;  
   task automatic t(virtual I vif);
   endtask
endclass

module top;
endmodule

results in

%Error-UNSUPPORTED: bug.sv:5:29: Unsupported: virtual interface never assigned any actual interface
    5 |    task automatic t(virtual I vif);
      |                             ^

Both with the following arguments:

verilator --timing --trace-fst --top-module top --binary bug.sv

@wsnyder
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wsnyder commented Jul 22, 2024

As it says this isn't currently supported. I presume your request is to add support for this.

@kozdra is there a reason we can't just ignore unused virtual interfaces like this?

@wsnyder wsnyder added status: ready Issue is ready for someone to fix; then goes to 'status: assigned' type: feature-IEEE Request to add new feature, described in IEEE 1800 and removed new New issue not seen by maintainers labels Jul 22, 2024
@wsnyder wsnyder changed the title Unsupported: virtual interface never assigned any actual interface Support unassigned virtual interfaces Jul 22, 2024
@kozdra
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kozdra commented Jul 23, 2024

Use of an actual interface as a value of virtual interface dtype is required in V3LinkDot, because unused interfaces are marked dead and not resolved correctly afterwards.
We could try to mark them as not dead, but I am not sure if just doing it would work without plugging them as used cells anywhere. If I remember correctly, further stages might assume that interfaces are either dead or used by actual cells, in that case this feature would require modifying their checks.

@wsnyder wsnyder mentioned this issue Mar 11, 2025
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@wsnyder
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wsnyder commented Apr 26, 2025

BTW if #2227 is fixed, Verilator will detect the unused class and this error will go away in the cases mentioned.

@wsnyder wsnyder mentioned this issue Apr 26, 2025
Closed
@wsnyder wsnyder marked this as a duplicate of #5960 Apr 26, 2025
@solomatnikov
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More examples from https://github.com/pulp-platform/common_cells

%Error-UNSUPPORTED: common_cells/test/stream_test.sv:26:13: Unsupported: virtual interface never assigned any actual interface
   26 |     virtual STREAM_DV #(
      |             ^~~~~~~~~
                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=5.037
%Error-UNSUPPORTED: common_cells/test/stream_test.sv:31:15: Unsupported: virtual interface never assigned any actual interface
   31 |       virtual STREAM_DV #(
      |               ^~~~~~~~~

This was referenced May 8, 2025
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