Busywork

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My first small business wasn’t actually in the software industry. Back when I was a student, I did contract office jobs in the summer holidays to pay for things while I was studying. I got a feeling that I’d be happier self-employed than someone else’s employee, so after graduation I experimented with registering an Australian Business Number (ABN) and using it to do maths and sciences tuition. I went back to working for other companies eventually, but I learned a lot from the experience, and that know-how was extremely valuable later when I quit my full-time job to start my own little consulting business.

I might write more about that experience some other time, but for now I want to write about what’s been hardest for me to get used to: when you’re self-employed, no one cares how much work you do.

The Enterprise Pushbutton

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Let’s talk about a hardware driver for a pushbutton. A pushbutton driver isn’t as completely trivial as it might sound because you need debouncing logic to ensure a crisp on/off signal, but it’s hard to imagine how it might need more than about 100 lines of C code.

After working on this particular embedded system, I didn’t need to stress my imagination any more. This pushbutton driver was modelled as an explicit finite state machine, and all the possible states and transitions were specified in a spreadsheet. Then there was a python script that processed this spreadsheet and generated state table data as C code. This was linked to an FSM evaluator in C. The FSM was controlled by a bare-metal driver and triggered callbacks on each state transition.

Most of the callbacks were marked “not yet implemented”. In fact, only two states were even reachable: BUTTON_UP and BUTTON_DOWN. Eventually the entire project was canned, but not because of missing support for BUTTON_TIMEOUT or any of the other states.

Oh, yeah, the FSM didn’t do any debouncing, so the low-level driver had to do that before passing button up/down events to the FSM.

Why Defensive Coding Matters - A War Story

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Story time.