I don't think this falls into the atomic category. (Although it blew up in my face.)

As I understand it, "atomic operations" ensure that nothing can change a variable as you're operating on it. The is important if you're accessing a 16-bit variable on an 8-bit machine. For instance, something like:

unsigned int foo, bar;
void main(void) {
    foo = 2;
    bar = foo;
} // main

The issue here is that there's no simple one-step move operation that copies bletch into snafu. Both variables require more than one access (one to get the lower-order byte and copy it, one to get the higher-order byte and do same). If an interrupt came along and modified foo during the copy operation, you'd get a wrong answer.

We know the solution to this is to disable interrupts around the copy.

But I'm not sure if my example is really "atomic." Maybe it's semantic hair-splitting.

I guess that disabling interrupts in the isUartEOL() function would have solved the problem.

-a