gEDA-user: Verilog, testbenches, and Makefiles

[Larry Doolittle <ldoolitt@xxxxxxxxxxxxxxx>]

I just finished cleaning out some lint on some Verilog code
and infrastructure, and thought it might be nice to share some
of my techniques.

Context is Icarus Verilog, gtkwave, and running regression-style
testbenches on production synthesizable FPGA code.

Suppose we have a synthesizable foo.v, that instantiates a module
from bar.v.  For consistency, put the testbench for foo in foo_tb.v.
Make sure foo_tb.v prints out either PASS or FAIL.
The heart of the Makefile is a set of four general rules:

%_tb: %_tb.v
	iverilog -Wall -DSIMULATE ${VFLAGS_$@} $^ -o $@

# Generic regression test
%_check: %_tb testcode.awk
	vvp $< | awk -f $(filter %.awk, $^)

%.vcd: %_tb
	vvp $<

# Useful for those testbenches that have a corresponding .sav file
%_view: %.vcd %.sav
	gtkwave $^

To make this apply properly to foo, all you need to add is:

foo_tb: foo.v bar.v

At which point "make foo_check" will compile and run the testbench,
using the following testcode.awk program to signal success or failure
to make(1):

--cut here--
# very general processing of vvp output to set a return code
# since apparently Verilog running inside vvp does not have
# a way to affect that directly
BEGIN{code=1}
/PASS/{code=0}
{print $0}
END{exit(code)}
--cut here--

If you have extra compile flags peculiar to this testbench, perhaps
for floating point support, you can add them like this:

VFLAGS_foo_tb = -m va_math

When the testbench works properly, add "foo_check" to the all: line
of the Makefile.  If you use gtkwave to inspect the waveforms for
problems, on your way to developing a true PASS/FAIL output of the
testbench, save the gtkwave configuration in foo.sav.  Then you can
recompile, rerun the simulation, and bring up a fresh gtkwave screen
with the single command "make foo_view".

Finally, the Makefile can end with a superset of:

clean:
	rm -f *_tb *.vcd

That's it!  I started using Icarus and Makefiles heavily about four
years ago, and have gradually worked my way up to this point.  This
template is compatible with the pristine-source paradigm using VPATH.
My current project has ten _check targets for the various components
that make up the final design; five of them are exactly as presented
above, the other five have more specialized post-processing.

I welcome discussion and suggestions for improvement.

   - Larry


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