R/~W

(read/not write) A signal that indicates the type of transfer on a bidirectional bus. If the signal is set, the transfer will be a read. If the signal is reset, the transfer will be a write. Short for Read/Not Write. The read and write signal need not be combined in this way, though it is a common way to reduce a processor s pin count by one. The write signal is active low hence, the not write in its name.

Rabbit 2000

num. A modern microcontroller variant of the now ancient Z80 architecture.

race condition

1. n. A situation in which the combined effects of two or more programmatic threads (or a single thread and an ISR) varies depending on the precise order in which the instructions of each are executed.

Race conditions can be eliminated by surrounding critical code sections that must be executed without interruption with a pair of mutex take and release system calls. To prevent race conditions involving ISRs, interrupts must be disabled for the duration of the critical section.

Example: If two threads both try to increment a shared global variable ( x = x + 1;) and they race, the result of both threads incrementing the variable once from an initial value ( x = 0;) can be either 2 (correct) or 1 (incorrect).

This race condition exists if either increment step is not executed atomically. If a context switch occurs in the middle of an increment (which is typically a sequence of...