Yes, this document Redirecting answered about half of my questions. The other half has more to do with the runtime environment. I gather that the arduino core calls setup() and then repeatedly calls loop(). OK. How big is my stack? Is anything else initialized? Is "it" compatible with standard gcc library functions, or do some of those need to be avoided? What does the runtime do, or what can I get it to do, in between "loop()" invocations? Why this particular structure? I guess part of the idea is to simplify C/C++? What things can I count on having the environment do well for me, and what things must I revert to "real C" for? Are there C and/or C++ structures that must or should be avoided? If it's so flexible, how come no one has written and arduino core for the Butterfly board? Um... that'll do for now.