Monday, January 29, 2018

New Peer Review Checklist for Embedded C Code

Here's a new peer review checklist to help improve the quality of your embedded C code.

To use the checklist, you should do a sit-down meeting with, ideally, three reviewers not including the code author. Divide the checklist up into three portions as indicated.  Be sure to run decent static analysis before the review to safe reviewer time -- let the tools find the easy stuff before spending human time on the review.

After an initial orientation to what the code is supposed to do and relevant background, the review process is:
  1. The review leader picks the next few lines of code to be reviewed and makes sure everyone is ONLY focused on those few lines.  Usually this is 5-10 lines encompassing a conditional structure, a basic block, or other generally unified small chunk within the code.
  2. Reviewers identify any code problems relevant to their part of the checklist.  It's OK if they notice others, but they should focus on individually considering each item in their part of the checklist and ask "do I see a violation of this item" in just the small chunk of code being considered.
  3. Reviewer comments should be recorded in the form: "Line X seems to violate Checklist Item Y for the following reason." Do NOT suggest a fix -- just record the issue.
  4. When all comments have been recorded, go back to step 1.  Continue to review up to a maximum of 2 hours. You should be covering about 100-200 lines of code per hour. Too fast and too slow are both a problem.
A text version of the checklist is below. You can also download an acrobat version here.  Additional pointers to support materials are after the checklist. If you have a static analysis tool that automates any of the checklist item, feel free to replace that item with something else that's important to you.

Peer Review Checklist: Embedded C Code
Before Review:
0    _____    Code compiles clean with extensive warning checks (e.g. MISRA C rules)
Reviewer #1:       
1    _____    Commenting:  top of file, start of function, code that needs an explanation
2    _____    Style is consistent and follows style guidelines
3    _____    Proper modularity, module size, use of .h files and #includes
4    _____    No orphans (redundant, dead, commented out, unused code & variables)
5    _____    Conditional expressions evaluate to a boolean value; no assignments
6    _____    Parentheses used to avoid operator precedence confusion
7    _____    All switch statements have a default clause; preferably an error trap
Reviewer #2:       
8    _____    Single point of exit from each function
9    _____    Loop entry and exit conditions correct; minimum continue/break complexity
10    _____    Conditionals should be minimally nested (generally only one or two deep)
11    _____    All functions can be unit tested; SCC or SF complexity less than 10 to 15
12    _____    Use const and inline instead of #define; minimize conditional compilation
13    _____    Avoid use of magic numbers (constant values embedded in code)
14    _____    Use strong typing (includes: sized types, structs for coupled data, const)
15    _____    Variables have well chosen names and are initialized at definition
Reviewer #3:       
16    _____    Minimum scope for all functions and variables; essentially no globals
17    _____    Concurrency issues? (locking, volatile keyword, minimize blocking time)
18    _____    Input parameter checking is done (style, completeness)
19    _____    Error handling for function returns is appropriate
20    _____    Null pointers, division by zero, null strings, boundary conditions handled
21    _____    Floating point use is OK (equality, NaN, INF, roundoff); use of fixed point
22    _____    Buffer overflow safety (bound checking, avoid unsafe string operations)
All Reviewers:     
23    _____    Does the code match the detailed design (correct functionality)?
24    _____    Is the code as simple, obvious, and easy to review as possible?
        For TWO Reviewers assign items:   Reviewer#1:  1-11; 23-24    Reviewer#2: 12-24
        Items that are covered with static analysis can be removed from checklist
        Template 1/28/2018:  Copyright CC BY 4.0, 2018, Philip Koopman

Additional material to help you with successful peer reviews:


  1. One addition I'd like to suggest is to incorporate static analysis tool output in the review checklist. In other words: When a piece of code is reviewed, the reviewers also review the warnings that the static analysis tool provides (buffer overruns, data taint, concurrency issues, null pointer dereference, ...) and make sure that they are properly assessed.

    Thanks for the post
    Mark Hermeling [GrammaTech]

    1. That's basically the point of item #0. An entry criterion for peer review is that you've done static analysis and fixed the warnings you are supposed to fixed. I'm an advocate of being completely warning-free for a defined set of application-appropriate warnings, so all you need to do then is make sure that the warning check has turned up clean.
      If you want to enter peer review without outstanding warnings you can/should then make evaluating the warnings one of the topics. However, in my experience if you have more than a handful of warnings this becomes impractical, and you end up with with the warnings changing so much after every code modification people just give up. Much better would be to permit pragmas to selectively turn off warnings for the few exceptions (i.e., document deviations from the rules) and make peer review of the correctness and appropriateness of those deviations/pragmas part of the review process.


Please send me your comments. I read all of them, and I appreciate them. To control spam I manually approve comments before they show up. It might take a while to respond. I appreciate generic "I like this post" comments, but I don't publish non-substantive comments like that.

If you prefer, or want a personal response, you can send e-mail to
If you want a personal response please make sure to include your e-mail reply address. Thanks!