interface

I think I missed a step in the 'OR' clause:

EITHER
   1. Hire consultant to do it for you; eg,
      " device
      This will tell you what the device requires for its operation;

   2. Study the documentation for the "controller" device
      This will tell you what features and facilities the device provides for you to use;

   3. Think about how you can apply the facilities of the "controller" (see 2) to
      meet the requirements of the "peripheral" (see 1);

   4. Study the documentation for any tools, etc, that you will be using
      eg, assemblers, compilers, etc

   5. Do it!
END.

I think I missed a step in the 'OR' clause:

EITHER
   1. Hire consultant to do it for you; eg,
      " device
      This will tell you what the device requires for its operation;

   2. Study the documentation for the "controller" device
      This will tell you what features and facilities the device provides for you to use;

   3. Think about how you can apply the facilities of the "controller" (see 2) to
      meet the requirements of the "peripheral" (see 1);

   4. Study the documentation for any tools, etc, that you will be using
      eg, assemblers, compilers, etc

   5. Do it!
END.

You forgot a potential "break" statement in your flow chart.

"Consider if the selected processor (or peripherial) is really suited for the task. Potentially switch to other hardware, or consider giving up because the cost (amount of time and/or money required) is too high.

As I've said before, handling the "everything works fine" route is (almost) trivial - it's handling all the "exceptions" that make up 90% of the work!

The difference between "sample code" posted on websites and real, commercial-grade, software fit for release is, usually, the 90%...

I wouldn't want to spoil that tradition!

;-)