Globally asynchronous locally synchronous (GALS), in

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

, is an architecture for

designing A design is a plan or specification for the construction of an object or system or for the implementation of an activity or process or the result of that plan or specification in the form of a prototype, product, or process. The verb ''to design'' ...

electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electric ...

s which addresses the problem of safe and reliable

data transfer Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point o ...

between independent clock domains. GALS is a

model of computation In computer science, and more specifically in computability theory and computational complexity theory, a model of computation is a model which describes how an output of a mathematical function is computed given an input. A model describes ...

that emerged in the 1980s. It allows to design computer systems consisting of several synchronous islands (using synchronous programming for each such island) interacting with other islands using

asynchronous communication In telecommunications, asynchronous communication is transmission of data, generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data f ...

, e.g. with FIFOs.

Details

A GALS circuit consists of a set of locally synchronous modules communicating with each other via asynchronous wrappers. Each synchronous subsystem ("clock domain") can run on its own independent clock (frequency). Advantages include much lower

electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...

(EMI). The

CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOS ...

circuit (logic gates) requires relatively large supply current when changing state from 0 to 1. These changes are aggregated for

synchronous circuit In digital electronics, a synchronous circuit is a digital circuit in which the changes in the state of memory elements are synchronized by a clock signal. In a sequential digital logic circuit, data are stored in memory devices called flip-f ...

as most changes are initialised by an active clock edge. Therefore, large spikes on supply current occur at active clock edges. These spikes can cause large electromagnetic interference, and may lead to circuit

malfunction A malfunction is a state in which something functions incorrectly or is obstructed from functioning at all. Some types of malfunctions are: *Malfunction (parachuting), malfunction of a parachute * Sexual malfunction, also called "sexual dysfunct ...

. In order to limit these spikes large number of

decoupling capacitor A decoupling capacitor is a capacitor used to decouple one part of an electrical network (circuit) from another. Noise caused by other circuit elements is shunted through the capacitor, reducing its effect on the rest of the circuit. For hig ...

s are used. Another solution is to use a GALS design style, i.e. design (locally) is synchronous (thus easier to be designed than

asynchronous circuit Asynchronous circuit (clockless or self-timed circuit) is a sequential digital logic circuit that does not use a global clock circuit or signal generator to synchronize its components. Instead, the components are driven by a handshaking circui ...

) but globally asynchronous, i.e. there are different (e.g. phase shifted, rising and falling active edge) clock signal regimes thus supply current spikes do not aggregate at the same time. Consequently, GALS design style is often used in

system on a chip A system on a chip or system-on-chip (SoC ; pl. ''SoCs'' ) is an integrated circuit that integrates most or all components of a computer or other electronic system. These components almost always include a central processing unit (CPU), memory ...

(SoC).Zhoukun WANG and Omar HAMMAMI. "A 24 Processors System on Chip FPGA Design with Network on Chip"

/ref> It is especially used in network on a chip (NoC) architectures for SoCs. Some larger GALS circuits contain multiple CPUs. Generally each CPU in such an

asynchronous array of simple processors Asynchrony is the state of not being in synchronization. Asynchrony or asynchronous may refer to: Electronics and computing * Asynchrony (computer programming), the occurrence of events independent of the main program flow, and ways to deal wit ...

has its own independent oscillator. That oscillator can be halted when there's no work for its CPU to do. In some cases each CPU is further divided into smaller modules, each with their own independent clock, or in a few cases no clock at all ().

References

General

*
Dataflow Architectures for GALS
{{DEFAULTSORT:Globally Asynchronous Locally Synchronous Synchronization Digital circuits

Details

See also

References

General