cocotb: ability to force/freeze signal

Force/release would allow us to build a tool for what is called “testbench qualification” or “mutation coverage” - inject an error into the design, run a regression test and check that at least one of the tests finds the injected error. If the error is not detected, the testbench is too sloppy.

We could start by injecting stuck-at faults at the DUT ports (I have a pull request coming up for providing _is_port and _port_direction attributes for discovered objects).

This could be a good project for something like Google’s Summer of Code.

Ok, I will do a pull request with the changes.

Here’s the commit: https://github.com/lukedarnell/cocotb/commit/ad1d7c2fcff990970627b4c5e5a05ab24374fa36

It’s on top of a pretty old version, and porting to the latest master was non-trivial. Any volunteers to port this to the latest master?

@imphil @tonywmnix we do have changes with this functionality implemented as documented earlier in this issue. I’ll try and get a pull request to you in the next couple of days.

@s3bs we have a change that implements force, freeze, deposit and release.

The syntax is: dut.stream_in_ready <= Force(1) dut.stream_in_ready <= Release() dut.stream_in_ready <= Deposit(BinaryValue('x')) dut.stream_in_ready <= Freeze()

@chiggs @stuarthodgson Does that syntax make sense?

@lukedarnell Thank you for sharing, I’ll take a look! @themperek Yes, I’d be willing to help. Will come back to you as soon as I have an overview.

@lukedarnell any chance of trying out your patch? Sounds very intriguing!

@lukedarnell Any update on this?