AVR-GCC for Linux doesn't handle well 16 bit words

[DrDiettrich]

@fjrg76

When a variable has been declared volatile the compiler does:

1. Read the variable from the memory and save it into a register.
2. Process the register as need it.

I beg to differ, you describe the behaviour for non-volatile variables. Volatile variables are not kept in registers except for the evaluation of a single expression.