39% of Your Verification Budget Goes to What???

I used to drive a piece of garbage green 2000 Civic sedan. It sipped gas, was super reliable on the days it would start, and it didn’t matter how I abused it because it was already as bad as a driveable car could get. It was perfect for a guy like me who couldn’t care less about the vehicle he drove.

In November last year we bought a trailer. We needed a vehicle to pull it so I cashed in the crap-mobile (that’s what my kids called it) for a $50 tax receipt and upgraded to a 2004 4Runner. Somewhat unexpectedly, I’ve turned into a “truck guy” in the 9 months since and my dream vehicle has become a new 4Runner TRD PRO.

A 2017 Toyota 4Runner costs $44,440; that’s the TRD PRO model with the roof rack and alloy wheel options. Because my aversion to spending money is stronger than my love for dream vehicles, I’ve decided I can’t afford that. But I’d still like to drive one so I have to find a way other than paying for one myself. I think I found it… Continue reading

The Time It Takes To Find A Bug

How much time passes between writing a line of RTL or testbench code and knowing that it works. I know it varies, but on average how long would it take? A line of code is written, time passes, then a test is run that either verifies it’s correct or discovers a bug. Does that time pass as minutes? As days? Maybe weeks? Months?

I’m preparing for a talk at DAC next week in the Verification Academy booth and in going through my material I’ve started asking myself that question. It’s the 3rd year in a row the folks at Mentor have invited me for a session in the booth. The last 2 years have been a lot of fun and I’m hoping for the same this year. This year’s session is called Add Unit Testing To Your Verification Toolbelt. As the name suggests, the focus will be on how we can use unit testing and test-driven development to improve the quality of the hardware we build.

I believe quite strongly in the value of unit testing and test-driven development because the quality of what I produce as a verification engineer is noticeably better because of them. I believe so strongly in TDD in particular that I know I get a little preachy at times. It’s the most important engineering skill I’ve ever learned and I don’t shy away from telling people about it.

I always think of rigour first when it comes to benefits. Testing code as you write it a few lines at a time is a rigorous process to say the least. But during the run-up to DAC I’m starting to think it’s timing that’s the real key. With TDD, the amount of time that passes between writing and testing a line of code is minutes, sometimes less. A design and test cycle measured in minutes is almost too short a time to think about anything else. I focus on getting exactly 1 thing right. There’s no thinking back, no back-and-forth with a teammate that found a bug, flipping through my logbook for clues as to what I’ve done or editing bug reports. In fact, with TDD there’s hardly any context switching at all. I write a line or 2, test them, if they’re broken I fix them, then I move to the next line. Most of the bugs I create are killed immediately; which coincidentally is the best time to kill them.

I’ve seen a lot of people talk about how bugs become more costly to fix the longer they live. For me, TDD has been the most effective way to respond.

If you’re at DAC next week in Austin and using TDD to kill bugs fast sounds good – or great! – I hope to see you at Mentor’s Verification Academy Booth at 11am on Monday. It’ll be a half hour presentation with lots of time for discussion. We’ll talk about TDD, unit testing, SVUnit and all the frustration that magically vanishes because of them!

Here’s a link to the session info for mine and others in the booth on VerificationAcademy.com.

See you at DAC!


Take The Um Out Of Scrum

Scrum is big in software and it’s slowly creeping into hardware development. To me this is good news because Scrum would be a transformative for hardware teams. In an industry that relies heavily on the big bang, iteratively coming to potentially shippable checkpoints, as a team would do with Scrum, would be a welcome change. It would give users and customers early access to product (or some version of a product depending on the technology involved), there’d be increased opportunities for feedback and the narrowed sprint-to-sprint focus on feature subsets would propel a significant improvement in quality.

Yes, Scrum would be great for hardware teams… unless, of course, we strip out the practices and objectives that make it effective and bend the rest around practices we already use without actually changing much. That would be less great. Continue reading

Definition of (De)Bug

In 9 years of blogging, I’m guessing at least half of what I’ve written centered around code quality or debug. For all the writing and time I’ve put into these topics, it took me until yesterday, for whatever reason, to realize I’m without a solid definition for debug. Or even a definition for bug for that matter. I guess I was relying on a common understanding of what bugs are and what it means to debug code. Realizing that may not be the case, I came up with a definition that captures what bugs are to me…

Bug: A state where a feature is defined, implemented and/or expected to fulfill a specific purpose but fails to do so.

Continue reading

I Can’t Hide From Unit Tests

There are times when I try and convince myself that unit testing my verification IP may not be necessary. Believe it or not, I can put together a pretty convincing argument. On a good day I shake it off and do the right thing. Other times I’m just convincing enough. I know it won’t end well, but I skip the unit tests and go straight to the code.

Here’s a couple arguments I’ve used on myself to get into trouble. Continue reading

Agile Hardware Kickstart

I had a neat opportunity to do a lunch-n-learn with a large group of engineers a few weeks ago. It was organized by the IEEE Computer Society as part of a program they use to pair engineering teams with various speakers and topics. They found me through a referral from an agile software friend of mine. I pitched a topic that sounded interesting enough so it was all systems go. I flew in for a day the third week of november. We had 250 people tune in. Good realtime feedback and a great experience for me.

I’ve done webinars like this in the past but I’ve never felt like I left people with a solid feel for how they get started with agile hardware. I wanted this time to be different; I wanted to boil the mess of information that floats around in my head down to concrete possibilities; I wanted those listening to go back to their desks feeling like they had the gumption to get something started. Continue reading

Verilog/VHDL Mixed Language Unit Testing


SVUnit supports mixed language Verilog/VHDL unit testing.


Download the Latest Version of SVUnit from GitHubIt didn’t take much to do it but for some reason it took me a loooooooong time to get at it. It involves a new switch to the runSVUnit command line. Users can now specify a ‘-m <vhdl file list>’ where vhdl file list is all their VHDL files and extra VHDL-related command line switches. It’s been tested with Modelsim and Incisive. Probably works with VCS though I can’t say for sure because I haven’t seen it with my own eyes. If someone wanted to give VCS a try and let me know what happens, I’d appreciate it!

The updated runSVUnit usage is (emphasis on -m|–mixedsim <vhdlfile>):


As an example, if you’re unit testing a mixed language design with Modelsim where VHDL files in your design are listed in myVHDL.f and your Verilog files are in myVerilog.f, your command line would be…

runSVUnit -s modelsim -m myVHDL.f -f myVerilog.f

As always, if there’s any trouble with it you can log an issue on github, send me an email at neil.johnson@agilesoc.com or leave something in the comments. If you were waiting on mixed language support to get started with SVUnit, now is your chance. Just scroll up and hit the big blue button to get started!

Happy unit testing!