Why isn't volatile sufficient here? If they were both modifying the same variable, I can see how A:read Ax; (Interrupt: B:read Bx; B:write Bx+1; return); A:

Why isn't volatile sufficient here? If they were both modifying the same variable, I can see how A:read Ax; (Interrupt: B:read Bx; B:write Bx+1; return); A: write Ax+1 # (wrong!) could occur. But the only error I can see here is that sometimes put() might fail thinking there is overflow when there's maybe one space left. Am I missing something? (Further investigation: This[1] thread suggests you can run into problems if your counter type is larger than the native ALU size, because the interrupt could occur midway through your increment operation. But here the size_t is 16 bits, so that should 't be a problem?) [1] http://www.embeddedrelated.com/showthread/msp430/20400-1.php http://www.embeddedrelated.com/showthread/msp430/20400-1.php