Allow write_lakeroad backend to write output to file instead of stdout.

[thiskappaisgrey]

Add code to allow write_lakeroad backend to write to file instead of stdout.

Example (in example.ys):

read_verilog <<EOF
module test(input [1:0] a, input b, output o);
  assign o = a & b;
endmodule
EOF

# Write output to file instead of stdout
write_lakeroad file.egg

@gussmith23

[gussmith23]

When we run this test, it will generate a "junk" output file. If we run the tests with a clean git directory (that is, no changes made, all changes committed), it will become dirty. This isn't ideal. There are a few ways to fix this:

• Delete the file after it's written. Unsure if this can be done from within a Yosys script. Sometimes scripting languages let you run shell commands, e.g. by prefixing with ! (like !rm file.egg). Maybe see if this is the case in yosys? (from my simple test on my command line, this is the case!)
• Generate the file to a temporary directory. This would also require getting the temporary directory within the Yosys script. Normally in a shell script this can be done e.g. with mktemp, but I'm not sure how to make that available in Yosys.
• Add the generated file to the .gitignore (less ideal).
• Just add functionality for writing to a file, but don't test it. (Obviously testing everything is ideal, so this is the worst option.)

These are intentionally ordered best to worst. I think the first option should work -- can you try it?

[gussmith23]

Suggested change

	# Write output to file instead of stdout
	write_lakeroad file.egg
	# Write output to stdout
	# write_lakeroad
	write_lakeroad
	write_lakeroad file.egg
	!rm file.egg

We might as well test both writing to a file and writing to stdout. Also added code solving my requested change above.

[gussmith23]

Suggested change

	// Copied from firrtl code. Not sure why "filename" is not set ever
	// even when I pass "write_lakeroad hello.egg" or something
	// Copied from firrtl code.

I'll explain to you why filename is not set, and then we can delete this comment (b/c the comment isn't actually relevant to the code). the filename variable isn't set because, when you call write_lakeroad from the Yosys shell (which is how you've been calling it), the Yosys internals call execute without passing filename. I don't know where in the Yosys codebase execute is ever called with a filename, but there must be some place where it's used. When you do write_lakeroad hello.egg, Yosys puts hello.egg into args, not into filename. (that's why this block of code exists: it basically says, if filename isn't set explicitly, then use the last argument as a filename)

[gussmith23]

Thanks!! A few comments and then we can merge.

[gussmith23]

Bump on this! Would love to merge it and don't want it to go stale.

[thiskappaisgrey]

@gussmith23 sorry for forgetting! I was busy with TA duties for the past couple of days (end of quarter is always crazy).

[gussmith23]

@gussmith23 sorry for forgetting! I was busy with TA duties for the past couple of days (end of quarter is always crazy).

No problem at all. Classes and TAing is more important! Just wanted to make sure it didn't get forgotten. Congrats on finishing your quarter!