Page 184 - The Art of Designing Embedded Systems

Troubleshooting 171

work, I start testing VO interfaces by writing low-level drivers and exer-
cising the code, making software and hardware changes in parallel as
needed. The code changes much faster than the wiring, so it seems waste-
ful to keep an iron hot all the time. Several companies sell neat $30 cord-
less soldering irons that heat in seconds, the ideal thing for those infrequent
modifications.
Being an immensely stupid person, I require vast quantities of clip
leads. Most of my ideas are wrong, so I save a ton of time by using a clip
lead to try a design change and see what happens.
Clip leads have a very short lifetime in a development lab. Accidentally
connect Vcc to ground and the plastic tip melts horribly. I hate it when that
happens. We used to send a runner to Radio Shack occasionally to replenish
our supply but found that “the Shack” couldn’t keep up with our needs.
It’s better to buy 100 clips at a time and have a high-school kid sol-
der up 50 leads. You’ll have an infinite supply for a while, and may help a
fledgling engineer find his true vocation. (Bring a part-timer in from your
local high school to help maintain the lab. The cost is minuscule, the lab
will be better off for it, and you’ll show one more kid that there are alter-
natives to slinging burgers.)
Be sure your lab area is set up to ensure that you can also do serious
software development! Clearly, your computer must include the properly
installed compilers and assemblers needed for the project. Just as impor-
tant as quality hand tools are the debuggers, make utilities, and other soft-
ware resources needed to quickly and painlessly write, compile, and test
the code. Set up the environment with a Make utility so you can com-
pile/assemble without twiddling compiler switches.
Hardware design requires as much software support as does the
firmware. PALS, PLDs, and FPGAs let you create much of the hardware
design late in the game and so are a wonderful thing. Be sure your bench
is set up with all of the tools you need to edit and compile these.

Documentation
All too often the frenetic pace of debugging hardware tempts us to be
less than careful about writing down changes. Resist this temptation. Your
company is paying you to debug a prototype for one reason only: so it can
be turned into a working production system. If you carelessly forget to
document modifications, the company will need at least one additional
PCB revision, which you’ll have to debug all over again. This is a terrible
waste of money. A wise manager of such a documentation-free engineer
will either retrain or fire the individual.