Glossary

Find definitions for technical terms in our Embedded Systems Glossary.

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Embedded Systems Glossary: V

via

n. A copper trace that connects signals on two or more layers of a PCB.

void

res. Having no defined type. In function prototypes and definitions, C's void keyword is used to indicate the lack of a return value or parameters. In pointer creation and manipulation, it asks the compiler to forgo all possible knowledge of the type of data pointed to.

/*
 * A function with no parameters. 
 */
int func1(void)
{
    ...
    return (0);
}

/*
 * A function with no return value
 * and a pointer with no defined type.
 */
void func2(int a, int b)
{
    void * p = (void *) &a;
    ...
}

How not to avoid void

volatile

res. A C keyword that should be used to warn your compiler (particularly the optimizer) about any pointers that point to registers with volatile values. This will ensure that the actual value is reread each time the data is used. [more]

volatile

adj. Said of a value that can change without the intervention of software. For example, values within the registers of some I/O devices might change in response to external events. Similarly, the contents of global variables that are shared by two or more tasks or a task and an ISR can be considered volatile.

See also volatile.

volt

n. A standard unit of electromotive force. Abbreviated V. One volt is the electrical force between two points for which 1 ampere of current will do 1 joule of work.

HISTORY: Named for Alessandro Giuseppe Anastasio Volta (1745–1827).

voltage-controlled oscillator

n. An oscillator with an output frequency that is a function of an input voltage. Abbreviated VCO. VCOs are very useful for transforming analog data to digital and then transmitting the signal over a single wire.

VxWorks

(vee ex works) N. A commercial real-time operating system from Wind River Systems.

HISTORY: The "Vx" in VxWorks is short for VRTX. The product was originally a set of add-ons for the then-popular VRTX RTOS, rather than a direct competitor. A business dispute later caused Wind River Systems to write its own kernel and discontinue its previous practice of bundling the VRTX code and license.

See also Tornado.