A digital logic architecture that does not use a central timing clock to synchronize all the circuits in a chip. Called "asynchronous logic," such an architecture eliminates approximately 15% of the chip's circuits and 20% of its power requirement. [1]

Figure 1. The Overview of Clockless Chips

Figure 1 shows the clock is a tiny crystal oscillator that resides in the heart of every microprocessor chip. The clock is what which sets the basic rhythm used throughout the machine. The clock orchestrates the synchronous dance of electrons that course through the hundreds of millions of wires and transistors of a modern computer.

Such crystals which tick up to 2 billion times each second in the fastest of today's desktop personal computers, dictate the timing of every circuit in every one of the chips that add, subtract, divide, multiply and move the ones and zeros that are the basic stuff of the information age.

Conventional chips (synchronous) operate under the control of a central clock, which samples data in the registers at precisely timed intervals. Computer chips of today are synchronous: they contain a main clock which controls the timing of the entire chips. [2]

Clockless chips work

There are no purely asynchronous chips yet. Instead, today's clockless processors are actually clocked processors with asynchronous elements.

Clockless elements use perfect clock gating, in which circuits operate only when they have work to do, not whenever a clock ticks.

Instead of clock-based synchronization, local handshaking controls the passing of data between logic modules. The asynchronous processor places the location of the stored data it wants to read onto the address bus and issues a request for the information. The memory reads the address off the bus, finds the information, and places it on the data bus. The memory then acknowledges that it has read the data. Finally, the processor grabs the information from the data bus. Pipeline controls and FIFO sequencers move data and instructions around and keep them in the right order.

According to Jorgenson, "Data arrives at any rate and leaves at any rate. When the arrival rate exceeds the departure rate, the circuit stalls the input until the output catches up."

The many handshakes themselves require more power than a clock's operations. However, clockless systems more than offset this because, unlike synchronous chips, each circuit uses power only when it performs work.[3]

References:

1. https://www.yourdictionary.com/clockless-computing
2. https://www.seminarsonly.com/computer%20science/clockless%20chip.php
3. https://www.computer.org/csdl/magazine/co/2005/03/r3018/13rRUx0xPwk

Cite this article:

Thanusri swetha J (2021), The Overview of Clockless Chips, Anatechmaz, pp. 41