Questions to Ask: Software Architecture, Design, And Coding

The process involved in architecting, designing, and writing embedded software and firmware is complicated, but I believe may be guided with a set of questions which must be continually evaluated by the engineering team as software development proceeds forward. This post provides a few of the questions I might be considering during my personal process.

Architecture and System

  • Are product requirements substantially complete or will the product requirements likely change frequently? How does this impact the architecture?
  • Will this product be a one-off design or create the foundation for a family of related products?
  • Do the documented requirements represent only the end-user product expectations? What other users might have an interest in the software and product requirements?
    • Factory/manufacturing? Calibration? Configuration?
    • Serial numbers? Unique IDs?
    • Refurbishment?
    • Technical support?
    • Internal QA?
    • Internal Engineering debug?
    • Electronic/hardware required functionality?
    • Certifying authorities?
    • Business partners?
    • Government entities?
  • Does the product potentially impact human lives or safety?
  • Does the product manage sensitive data, such as financial or medical information? How should the architecture support protecting such information?
  • What specific functionality is required by the electronic/hardware design?
  • Does the product support networking or other electronic access? How will the architecture secure the network interface to prevent illicit access?
  • Does the product require real-time responsiveness? Are those requirements enumerated and justified?
  • What are the reliability requirements?
  • Will the product operate 24×7?
  • Which software language(s) will be required?
  • What open-source software will be included and how will the software architecture ensure license requirements are respected?
  • What is the size of the software engineering team? How does this impact the architecture documentation and review process?
  • Will the product and associated architecture require supporting software, such as custom packaging tools to create software update files?
  • What other system components will interact with the product? What requirements are derived from that system? Do the external system components provide a development environment? If not, how will the product engineering team confirm and test behavior without disrupting existing services?
  • What are the project management priorities: schedule, cost, or quality? Pick two. How does this impact the software architecture?

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Design

  • Does the module being designed have a clear purpose?
  • What is the role of the module being designed within the enclosing application?
  • What is the role of the module within the system?
  • What resources will this module require? What are the limits on those resources?
  • Which requirements will this module support or implement?
  • Does this software module violate or support the DRY principle?
  • Do any certifying authorities require design and requirements traceability?
  • How will (or will) the design be approved or reviewed by peers?
  • Does this module require repeated and ongoing use of dynamic memory? If so, why? How does this impact real-time requirements? Does this impact reliability requirements?
  • Are the methods or APIs of this module clear and easy to use correctly?
  • Does this module make use of any units of measurement? Are the units documented clearly, and if possible, enforced by the build system to prevent errors, including catastrophic errors?
  • Is this design over-engineered?
  • Should this module be refactored?
  • How large should the stack be for this module/thread? How will I test and confirm stack usage?

Coding

  • Did I write a test before coding? If not, why not? How will I test this code?
  • How will I debug this code?
  • Why is this code required?
  • Is there a coding standard? If not, why not? If not, will I create my own standard for this project?
  • Is this variable/function/class/method named clearly? Will I understand the name 9 months from now?
  • Does this section of code implement a documented industry standard? Do the code comments properly reference the standard?
  • Did this code “hack” around some hardware deficiency? Do the comments note the issue and why the hack was required?
  • Does this code operate in a multi-threaded environment? If so, how many threads might access this portion of the code? Is the code thread-safe? Can I prove it?
  • Will the code as written help prevent maintenance errors in the future?
  • Will this simple integer increment overflow? Do I care?
  • Did I just use CTRL+C and CTRL+V to author new code? Why? Should this code be refactored instead?
  • Is this routine too long?
  • Did I just use a magic number? Why? If the magic number is required by some hardware setup and configuration, does the code document the hardware reference where the magic number was found?
  • Am I proud of this code? Or would I feel compelled to offer excuses when the code is exposed to a peer?
  • Does this code impact the product’s real or soft timing requirements? How will the code contribute to the requirement? How will this be measured?
  • Did I just fix a bug reported by the end user or customer? How did I create that bug in the first place? How can I prevent the creation of that bug in the future? Have other bugs recently been fixed in this same code?
  • Does the code use recursion? Why? What is the impact on stack usage?
  • Can I read this code easily or do I need a reference book to comprehend the acronym soup?
  • Are the code comments professional and clean? Would I be comfortable with a jury of my peers reading those comments in a court of law?
  • Are the code comments providing appropriate meta-information, or are they simply repeating what is evident from the code itself?
  • Does the code use various C string functions, potentially exposing end customers to serious security flaws?
  • Does this code have an off-by-one error?
  • Is it time to stop thinking and start writing code?
  • Did I stop thinking too soon?
  • The code written allocates an object on the stack. How large is that object? Is that acceptable in this thread’s stack context?
  • That C struct allocated on the stack: was it initialized correctly? Was every field initialized correctly?
  • Did function correctly check the bounds of the input arguments? Are the inputs valid?
  • What is the context of this code? A thread? An interrupt service routine (ISR)? A Timer callback? What are the coding requirements when writing code in this context?

That list seems long enough for now! What would you add to the list?

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Related post: The Matthew Test: 15 Steps to Better Embedded Software (and Firmware)

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