Agile Hardware Starts As A Steel Thread

For me, a key to agile is incremental development. Most software developers reading this will probably say “duh… no kidding” but it’s a new concept to hardware folks.

If you’re new to agile, incremental development is something I’ve talked about in several articles on In a nutshell, it’s where product features are designed, implemented, tested and ready to go in small batches. Products start small but functional then grow in scope until they are delivered (they can also be delivered *as* they grow but I’m not going there today).

Because most hardware teams are used to developing products as big bang feature sets, incremental development can be a big step. To help teams get started, I put together an article called Operation Basic Sanity: A Faster Way To Sane Hardware that spells out how a team can deliver a small batch of features equivalent to a functionally sane device. That article was actually inspired by an exercise I called the “Steel Thread Challenge”.

Steel Thread is a term I’ve seen to describe some minimal thread of functionality through a product. I think about it as being able to <do something simple> to <some input> so that <something basic> happens on <some output>. As a hardware guy, a steel thread seems synonymous with a sane design. It’s small relative to what remains but significant in that you know the design is doing something right.

The Steel Thread Challenge: How-to

What You Need: The Steel Thread Challenge is a retrospective exercise that works back from a finished product. Choose a design that you’ve just finished or is at least well into development. You’ll also need a conference room with some whiteboard space.

Who You Need: You’ll focus on front-end development so include designers, verification engineers and modeling experts as well as the system architects and managers.

Step 1: Describe the product: On a whiteboard, draw a block diagram that includes the design and test environment. You should end up with something like this (except the blocks should be labelled)…

Step 2: Find the steel thread: Decide as a group what constitutes a steel thread (HINT: it should be a simple function that provides some tangible outcome). Identify the main processing path of the Steel Thread by drawing a line through your block diagram. That should get you to this point…

Step 3: Remove everything you don’t need: The goal is to find the smallest code footprint that supports the Steel Thread. By analyzing how your Steel Thread travels through the design and test environment, erase everything that isn’t needed (best to take a picture of what you have so you can redraw it if necessary!). First erase entire blocks if you can. If logic can be moved or simplified to remove entire blocks, make a list of necessary simplifications and then erase those blocks. From the blocks that remain, make a list of the features that aren’t necessary and could be ripped out. That should leave you with a list of what’s been removed and a diagram like this…

Step 4: Planning for the steel thread: Now the “challenge” part of the Steel Thread Challenge. This is a mock planning exercise where as a group you discuss how you would build, test and deliver a Steel Thread starting from a clean slate. Pretend your Steel Thread is your product and you have to deliver it asap. How would you get there and how would it be different from what you normally do?

  • would the code you write be any different than usual?
  • would teamwork and/or organization be the same or different?
  • what would your schedule look like?
  • what would your documentation look like?
  • would your task assignments be any different than normal?
  • how long would it take to deliver the steel thread?
  • is there planning that could be delayed relative to what you normally do?

If you and your team try this exercise, I’d like to hear how it goes. If you have other ideas for helping people jump the “big bang to incremental development” hurdle, I’d like to hear that also! This will be a big step for many teams so the more options we have, the better!


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