2013年1月24日 星期四

System on a chip

Introduction

We all know an ordinary desktop mainly contains a CPU, RAM as main memory, hard disk as secondary storage, some related electronic components, and last but not least a motherboard which links the components together. However, can you imagine that all above components can place into the single chip? Tablets and smart phones both can use this technology to build their system in a chip. We would like to introduce “system on a chip”.

What is “System on a Chip”?

What is system on a chip? System means an integrated circuit, which integrates all components of a computer or other electronic system and build in a single chip by using the semi-conductor technology.

The purpose is to increase the performance, save the power and reduce the production costs.

Normally the components mainly include processor and memory. Other component will depend on the device. For a MP3 player it may include flash controller and audio codec also.

SOC is an application typical used in embedded system .Generally SOC is designed by application-specific integrated circuits (ASIC) and the architecture for the chip is fixed. For example the processor cannot be modified after embedded on the chip.

SOC is used almost everywhere, especially in small, increasingly complex consumer electronic devices, like smart phone, tablet, digital camera, information appliances etc.

Let’s give a case study to explain more

The emotion engine (SOC) for Sony PlayStation 2 which has two main functions:
  1. Behavior simulation
  2. Geometry translation
(Dirk Oppelt (2005), http://en.wikipedia.org/wiki/File:Sony_EmotionEngine_CXD9615GB_top.jpg)


It contains eight separate units. Each unit performs a specific task, integrated onto the same die.
These units are: a main processor of the Reduced Instruction Set Computer (RISC), two vector processing units (VPU), VPU0 and VPU1, each of them contains four parallel processors of single instruction multiple data stream (SIMD).
VPU0 is responsible for executing game code and high-level modeling computations. VPU1 is dedicated to geometry-transformations and lighting. A graphics interface (GIF), a 10 channel DMA unit, a memory controller, an Image Processing Unit (IPU) and an input output interface.


Architecture

The components in a SOC are quite similar with these in computer. However, because of the size of chip and the purpose of the chip, it may be greatly difference between them. A typical system on a chip may includes the following components:

Hardware


Processors

The processor usually runs with low power usage. The most common design of processor in system on a chip is ARM architecture which is RISC-based approach and is commonly used in embedded system. If there is more than one processor, this type of SOC will call multiprocessor system on chip (MPSOC).

Memory

Based on different purpose of SOC, the chip can include RAM, ROM and flash memory. In fact, memory spend large amount of area of SOC. According to other research, it said that "Memory content in SOC was increasing dramatically over the last years. In 2010, about 90% of the silicon area will consist of memories with different functionality"(Erik Jan Marinissen, Betty Prince, Doris Keitel-Schulz, Yervant Zorian, Challenges in Embedded Memory Design and Test, http://hal.archives-ouvertes.fr/docs/00/18/11/96/PDF/228820722.pdf)

Clock

As SOC is a complete electronic system and have its own processor, SOC can have its clock. However, SOC may use the external signal to be the clock signal.

I/O port or external interface

Sometimes, SOC need to connect other external device or coordinate with other SOC. For example, Some SOC is able to add Off-clip memory or SOC can contain USB to transmit data to external device.

Other component

Some SOC may contain audio, video, Wi-Fi device or other components to fulfill the needs of the system.

Software


Real-Time Operating System

As SOC contains different components in the system, some SOC have Real-Time Operating System (RTOS) to manage them. Notice that whether SOC contains RTOS is based on the design of SOC. Not all SOC should have the RTOS.

Driver

Some SOC may contain the driver to control the device on the chip such that OS can operate the device.

The development of SoC

The development of the integrated circuit has a 40-year history. Based on the Moore’s Law, the number of transistors in a modern SoC is increased double every 2 years. Integrating billions transistors can permit a wide range of functions. On our daily life, many types of device use SoC such as smart phones and tablets. In case of smart phones, more and more features are provided. The increase of functionality was due to the evolution of SoC.

As more transistors are integrated into a single chip, the power efficiency is one of the important parts of the SoC design. In order to have high performance with the lowest power consumption, one of the solutions is to reduce power consumption of clock distribution. Furthermore, parallel processing can be used without increasing power consumption. Additionally, multi-processor SoCs can increase processing capabilities. Integrate multiple programmable cores can provide high performance with flexibility at reduced system cost.

Greater device integration enables increasingly more complex system designs with longer design cycle times. Also, the cost of SoC development is high. Verification is the major part of the overall development cost and time. It led to fewer SoC designs in the semiconductor industry.

Benefits and Challenges of SoC

There must be lots of benefits of applying SoC. However, there may also be some drawbacks and challenges. Let’s look into some main issues of pros and cons of SoC.

We should notice the main benefit is the physical size of SoC. Their size is much smaller than a traditional design. It is because all the computer components are already fabricated into one single chip. This property facilitates the development of devices as they can become lighter and smaller. The smaller size can lead the lower cost because more chip can be produced in one silicon die.

As the computer components of SoC chip are fabricated into one single chip, the consequential major benefits are the reliability and power-saving. The system bus on the chip becomes much shorter than found in traditional design  since the components become much closer to each other. Therefore, the power consumption transmitting signals becomes much lower. Moreover, due to the short system bus, the data transmission can be guaranteed as data loss upon transmission is reduced. This is especially important in transmitting analogs as they are in the form of multi-level amplitudes.

Other main benefit on applying SoC is the flexibility on design SoC for particular uses. Specified design and implementation of SoC focusing on the purpose of the practical device. As this result, SOC can be high reusability because we can reuse the design of SOC if the device has similar purpose.

Despite the great benefits SoC has, we also need to face the drawbacks and challenges of developing SoC products.

An important challenge in developing SoC is time-to-market problem, which is a main issue developing commercial products. Since the complexity of the computer keep growing nowadays, manufacturers must be able to keep producing powerful, price-reasonable SoC products for customers. Moreover, the time taken for developing SoC is also a key component such that the SoC products can be developed in a short period.

Summary

SoC technology is a trend in developing various kinds of digital products. Although it has many benefits such as smaller size, lower cost and higher performance, the challenge developing is still an issue that we need to concern. Hopefully we can have an optimal solution between the pros and cons.

Exercise

Do all mobile devices use SOC? Can I design the mobile device without SOC?

Theoretically,you can design the mobile device without any SOC. However, the size of components will become greatly larger. The mobile device will be larger and the cost will also increase. Therefore, no one would like to develop the mobile device without SOC.

What is system on a chip?

System on a chip is the electronic system that embedded into a single chip.

What is embedded systems?

An embedded system is the specific computer system embedded into the device. It mean the components is fixed in the device and cannot be change easily.

What is the relation between system on a chip and embedded system?

System on a chip is one of the embedded system that build into a chip. In other words, system on a chip is the subset of the embedded system.

Reference

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