Add support for verilator

[krupan]

I'm willing to help add support for verilator as a simulation tool, but after spending a good amount of time trying to figure out how I'm just left with the same bad taste in my mouth for Makefiles that I always get

[krupan]

Here's what I know. verilator takes (system)verilog files as input and generates c++ code, some makefiles, and .d dependency files in a directory named obj_dir. You can then go into the obj_dir directory and run make to compile that c++ code into a simulation binary that you then execute to run your simulation.

They have examples of how to write a makefile to run verilator and make use of those generated .d files. You can see that here: https://github.com/verilator/verilator/tree/master/examples/make_tracing_c

What I can't quite figure out is how to integrate all that into this hdl_build system.

[krupan]

The generated .d files look something like this:

obj_dir/Vtop.cpp obj_dir/Vtop.h obj_dir/Vtop.mk obj_dir/Vtop__Syms.cpp obj_dir/Vtop__Syms.h obj_dir/Vtop__TraceDecls__0__Slow.cpp obj_dir/Vtop__Trace__0.cpp obj_dir/Vtop__Trace__0__Slow.cpp obj_dir/Vtop___024root.h obj_dir/Vtop___024root__DepSet_h84412442__0.cpp obj_dir/Vtop___024root__DepSet_h84412442__0__Slow.cpp obj_dir/Vtop___024root__DepSet_heccd7ead__0.cpp obj_dir/Vtop___024root__DepSet_heccd7ead__0__Slow.cpp obj_dir/Vtop___024root__Slow.cpp obj_dir/Vtop__pch.h obj_dir/Vtop__ver.d obj_dir/Vtop_classes.mk  : /usr/bin/verilator_bin /usr/bin/verilator_bin /usr/share/verilator/include/verilated_std.sv input.vc sub.v top.v 

or this:

Vtop__ALL.o: Vtop__ALL.cpp Vtop.cpp Vtop__pch.h \
 /usr/share/verilator/include/verilated.h \
 /usr/share/verilator/include/verilatedos.h \
 /usr/share/verilator/include/verilated_config.h \
 /usr/share/verilator/include/verilated_types.h \
 /usr/share/verilator/include/verilated_funcs.h Vtop__Syms.h \
 /usr/share/verilator/include/verilated_vcd_c.h \
 /usr/share/verilator/include/verilated.h \
 /usr/share/verilator/include/verilated_trace.h Vtop.h \
 /usr/share/verilator/include/verilated_cov.h Vtop___024root.h \
 Vtop___024root__DepSet_h84412442__0.cpp \
 Vtop___024root__DepSet_heccd7ead__0.cpp Vtop__Trace__0.cpp \
 Vtop___024root__Slow.cpp Vtop___024root__DepSet_h84412442__0__Slow.cpp \
 Vtop___024root__DepSet_heccd7ead__0__Slow.cpp Vtop__Syms.cpp \
 Vtop__Trace__0__Slow.cpp Vtop__TraceDecls__0__Slow.cpp
Vtop.cpp:
Vtop__pch.h:
/usr/share/verilator/include/verilated.h:
/usr/share/verilator/include/verilatedos.h:
/usr/share/verilator/include/verilated_config.h:
/usr/share/verilator/include/verilated_types.h:
/usr/share/verilator/include/verilated_funcs.h:
Vtop__Syms.h:
/usr/share/verilator/include/verilated_vcd_c.h:
/usr/share/verilator/include/verilated.h:
/usr/share/verilator/include/verilated_trace.h:
Vtop.h:
/usr/share/verilator/include/verilated_cov.h:
Vtop___024root.h:
Vtop___024root__DepSet_h84412442__0.cpp:
Vtop___024root__DepSet_heccd7ead__0.cpp:
Vtop__Trace__0.cpp:
Vtop___024root__Slow.cpp:
Vtop___024root__DepSet_h84412442__0__Slow.cpp:
Vtop___024root__DepSet_heccd7ead__0__Slow.cpp:
Vtop__Syms.cpp:
Vtop__Trace__0__Slow.cpp:
Vtop__TraceDecls__0__Slow.cpp: