Section 3.2. Integrated Processors: Systems on Chip

3.2. Integrated Processors: Systems on Chip

In the previous section, we highlighted stand-alone processors. Although they are used for many applications, including some high-horsepower processing engines, the vast majority of embedded systems employ some type of integrated processor, or system on chip (SOC). Literally scores, if not hundreds, exist to choose from. We examine a few from the industry leaders and look at some of the features that set each group apart. As in the section on stand-alone processors, we focus only on those integrated processors with strong Linux support.

Several major processor architectures exist, and each architecture has examples of integrated SOCs. PowerPC has been a traditional leader in many networking- and telecommunications-related embedded applications, while MIPS might have the market lead in lower-end consumer-grade equipment.^[4] ARM is used in many cellular phones. These represent the major architectures in widespread use in embedded Linux systems. However, as you will see in Chapter 4, "The Linux Kernel: A Different Perspective," Linux supports more than 20 different hardware architectures today.

^[4] These are the author's own opinions based on market observation and not based on any scientific data.

3.2.1. PowerPC

PowerPC is a Reduced Instruction Set Computer (RISC) architecture jointly designed by engineers from Apple, IBM, and Motorola's semiconductor division (now an independent entity spun off as Freescale Semiconductor). Many good documents describe the PowerPC architecture in great detail. Consult the "Suggestions for Additional Reading" at the end of this chapter as a starting point.

PowerPC processors have found their way into embedded products of every description. From automotive, consumer, and networking applications to the largest data and telecommunications switches, PowerPC is one of the most popular architectures for embedded applications. Because of this popularity, there exists a large array of hardware and software solutions from numerous manufacturers targeted at PowerPC.

3.2.2. AMCC PowerPC

Some of the examples later in this book are based on the AMCC PowerPC 440EP Embedded Processor. The 440EP is a popular integrated processor found in many networking and communications products. The following list highlights some of the features of the 440EP:

• On-chip dual-data-rate (DDR) SDRAM controller

• Integrated NAND Flash controller

• PCI bus interface

• Dual 10/100Mbps Ethernet ports

• On-chip USB 2.0 interface

• Up to four user-configurable serial ports

• Dual I²C controllers

• Programmable Interrupt Controller

• Serial Peripheral Interface (SPI) controller

• Programmable timers

• JTAG interface for debugging

This is indeed a complete system on chip (SOC). Figure 3-2 is a block diagram of the AMCC PowerPC 440EP Embedded Processor. With the addition of memory chips and physical I/O hardware, a complete high-end embedded system can be built around this integrated microprocessor with minimal interface circuitry required.

Figure 3-2. AMCC PPC 440EP Embedded Processor (Courtesy AMCC Corporation)

Many manufacturers offer reference hardware platforms to enable a developer to explore the capabilities of the processor or other hardware. The examples later in this book (Chapters 14, "Kernel Debugging Techniques"; and 15, "Debugging Embedded Linux Applications") were executed on the AMCC Yosemite board, which is the company's reference platform containing the 440EP shown in Figure 3-2.

Numerous product configurations are available with PowerPC processors. As demonstrated in Figure 3-2, the AMCC 440EP contains sufficient I/O interfaces for many common products, with very little additional circuitry. Because this processor contains an integrated floating-point unit (FPU), it is ideally suited for products such as network-attached imaging systems, general industrial control, and networking equipment.

AMCC's PowerPC product lineup includes several configurations powered by two proven cores. Their 405 core products are available in configurations with and without Ethernet controllers. All 405 core configurations include integrated SDRAM controllers, dual UARTs for serial ports, I²C for low-level onboard management communications, general-purpose I/O pins, and integral timers. The AMCC 405 core integrated processors provide economical performance on a proven core for a wide range of applications that do not require a hardware FPU.

The AMCC 440-based core products raise the performance level and add peripherals. The 440EP featured in some of our examples includes a hardware FPU. The 440GX adds two triple-speed 10/100/1000MB Ethernet interfaces (in addition to the two 10/100Mbps Ethernet ports) and TCP/IP hardware acceleration for high-performance networking applications. The 440SP adds hardware acceleration for RAID 5/6 applications. All these processors have mature Linux support. Table 3-1 summarizes the highlights of the AMCC 405xx family.

Table 3-1. AMCC PowerPC 405xx Highlights Summary

Feature	405CR	405EP	405GP	405GPr
Core/speeds	PowerPC 405	PowerPC 405	PowerPC 405	PowerPC 405
	133-266MHz	133-333MHz	133-266MHz	266-400MHz
DRAM controller	SDRAM/133	SDRAM/133	SDRAM/133	SDRAM/133
Ethernet 10/100	N	2	1	1
GPIO lines	23	32	24	24
UARTs	2	2	2	2
DMA controller	4 channel	4 channel	4 channel	4 channel
I2C controller	Y	Y	Y	Y
PCI host controller	N	Y	Y	Y
Interrupt controller	Y	Y	Y	Y
See the AMCC website, at www.amcc.com/embedded, for complete details.

Table 3-2 summarizes the features of the AMCC 440xx family of processors.

Table 3-2. AMCC PowerPC 440xx Highlights Summary

Feature	440EP	440GP	440GX	440SP
Core/speeds	PowerPC 440	PowerPC 440	PowerPC 440	PowerPC 440
	333-667MHz	400-500MHz	533-800MHz	533-667MHz
DRAM controller	DDR	DDR	DDR	DDR
Ethernet 10/100	2	2	2	via GigE
Gigabit Ethernet	N	N	2	1
GPIO lines	64	32	32	32
UARTs	4	2	2	3
DMA controller	4 channel	4 channel	4 channel	3 channel
I2C controller	2	2	2	2
PCI host controller	Y	PCI-X	PCI-X	three PCI-X
SPI controller	Y	N	N	N
Interrupt controller	Y	Y	Y	Y

3.2.3. Freescale PowerPC

Freescale Semiconductor has a large range of PowerPC processors with integrated peripherals. The manufacturer is currently advertising its PowerPC product portfolio centered on three broad vertical-market segments: networking, automotive, and industrial. Freescale PowerPC processors have enjoyed enormous success in the networking market segment. This lineup of processors has wide appeal in a large variety of network equipment, from the low end to the high end of the product space.

In a recent press release, Freescale Semiconductor announced that it had shipped more than 200 million integrated communications processors.^[5] Part of this success is based around the company's PowerQUICC product line. The PowerQUICC architecture has been shipping for more than a decade. It is based on a PowerPC core integrated with a QUICC engine (also called a communications processor module or CPM in the Freescale literature). The QUICC engine is an independent RISC processor designed to offload the communications processing from the main PowerPC core, thus freeing up the PowerPC core to focus on control and management applications. The QUICC engine is a complex but highly flexible communications peripheral controller.

^[5] On the Freescale website, navigate to Media Center, Press Releases. This one was dated 10/31/2005 from Austin, Texas.

In its current incarnation, PowerQUICC encompasses four general families. For convenience, as we discuss these PowerQUICC products, we refer to it as PQ.

The PQ I family includes the original PowerPC-based PowerQUICC implementations and consists of the MPC8xx family of processors. These integrated communications processors operate at 50-133MHz and feature the embedded PowerPC 8xx core. The PQ I family has been used for ATM and Ethernet edge devices such as routers for the home and small office (SOHO) market, residential gateways, ASDL and cable modems, and similar applications.

The CPM or QUICC engine incorporates two unique and powerful communications controllers. The Serial Communication Controller (SCC) is a flexible serial interface capable of implementing many serial-based communications protocols, including Ethernet, HDLC/SDLC, AppleTalk, synchronous and asynchronous UARTs, IrDA, and other bit stream data.

The Serial Management Controller (SMC) is a module capable of similar serial-communications protocols, and includes support for ISDN, serial UART, and SPI protocols.

Using a combination of these SCCs and SMCs, it is possible to create very flexible I/O combinations. An internal time-division multiplexer even allows these interfaces to implement channelized communications such as T1 and E1 I/O.

Table 3-3 summarizes a small sampling of the PQ I product line.

Table 3-3. Freescale Select PowerQUICC I Highlights

Feature	MPC850	MPC860	MPC875	MPC885
Core/speeds	PowerPC 8xx	PowerPC 8xx	PowerPC 8xx	PowerPC 8xx
	Up to 80MHz	Up to 80MHz	Up to 133MHz	Up to 133MHz
DRAM controller	Y	Y	Y	Y
USB	Y	N	Y	Y
SPI controller	Y	Y	Y	Y
I2C controller	Y	Y	Y	Y
SCC controllers	2	4	1	3
SMC controllers	2	2	1	1
Security engine	N	N	Y	Y
Dedicated Fast Ethernet controller	N	N	2	2

The next step up in the Freescale PowerPC product line is PowerQUICC II. PQ II incorporates the company's G2 PowerPC core derived from the 603e embedded PowerPC core. These integrated communications processors operate at 133-450MHz and feature multiple 10/100Mbps Ethernet interfaces, security engines, and ATM and PCI support, among many others. The PQ II encompasses the MPC82xx products.

PQ II adds two new types of controllers to the QUICC engine. The FCC is a full-duplex fast serial communications controller. The FCC supports high-speed communications such as 100Mbps Ethernet and T3/E3 up to 45Mbps. The MCC is a multichannel controller capable of 128KB x 64KB channelized data.

Table 3-4 summarizes the highlights of selected PowerQUICC II processors.

Table 3-4. Freescale Select PowerQUICC II Highlights

Feature	MPC8250	MPC8260	MPC8272	MPC8280
Core/speeds	G2/603e	G2/603e	G2/603e	G2/603e
	150-200MHz	100-300MHz	266-400MHz	266-400MHz
DRAM controller	Y	Y	Y	Y
USB	N	N	Y	Via SCC4
SPI controller	Y	Y	Y	Y
I2C controller	Y	Y	Y	Y
SCC controllers	4	4	3	4
SMC controllers	2	2	2	2
FCC controllers	3	3	2	3
MCC controllers	1	2	0	2

Based on the Freescale PowerPC e300 core (evolved from the G2/603e), the PowerQUICC II Pro family operates at 266-667MHz and features support for Gigabit Ethernet, dual data rate (DDR) SDRAM controllers, PCI, high-speed USB, security acceleration, and more. These are the MPC83xx family of processors. The PQ II and PQ II Pro families of processors have been designed into a wide variety of equipment, such as LAN and WAN switches, hubs and gateways, PBX systems, and many other systems with similar complexity and performance requirements.

The PowerQUICC II Pro contains three family members without the QUICC engine, and two that are based on an updated version of the QUICC engine. The MPC8358E and MPC8360E both add a new Universal Communications Controller, which supports a variety of protocols.

Table 3-5 summarizes the highlights of select members of the PQ II Pro family.

Table 3-5. Freescale Select PowerQUICC II Pro Highlights

Feature	MPC8343E	MPC8347E	MPC8349E	MPC8360E
Core/speeds	e300	e300	e300	e300
	266-400MHz	266-667MHz	400-667MHz	266-667MHz
DRAM controller	Y-DDR	Y-DDR	Y-DDR	Y-DDR
USB	Y	2	2	Y
SPI controller	Y	Y	Y	Y
I2C controller	2	2	2	2
Ethernet 10/100/1000	2	2	2	Via UCC
UART	2	2	2	2
PCI controller	Y	Y	Y	Y
Security engine	Y	Y	Y	Y
MCC	0	0	0	1
UCC	0	0	0	8

At the top of the PowerQUICC family are the PQ III processors. These operate between 600MHz and 1.5GHz. They are based on the e500 core and support Gigabit Ethernet, DDR SDRAM, RapidIO, PCI and PCI/X, ATM, HDLC, and more. This family incorporates the MPC85xx product line. These processors have found their way into high-end products such as wireless base station controllers, optical edge switches, central office switches, and similar equipment.

Table 3-6 highlights some of the PQ III family members.

Table 3-6. Freescale Select PowerQUICC III Highlights

Feature	MPC8540	MPC8548E	MPC8555E	MPC8560
Core/speeds	e500	e500	e500	e500
	Up to 1.0GHz	Up to 1.5GHz	Up to 1.0GHz	Up to 1.0GHz
DRAM controller	Y-DDR	Y-DDR	Y-DDR	Y-DDR
USB	N	N	Via SCC	N
SPI controller	N	N	Y	Y
I2C controller	Y	Y	Y	Y
Ethernet 10/100	1	Via GigE	Via SCC	Via SCC
Gigabit Ethernet	2	4	2	2
UART	2	2	2	Via SCC
PCI controller	PCI/PCI-X	PCI/PCI-X	PCI	PCI/PCI-X
Rapid IO	Y	Y	N	Y
Security engine	N	Y	Y	N
SCC			3	4
FCC			2	3
SMC			2	0
MCC			0	2

3.2.4. MIPS

You might be surprised to learn that 32-bit processors based on the MIPS architecture have been shipping for more than 20 years. The MIPS architecture was designed in 1981 by a Stanford University engineering team led by Dr. John Hennessey, who later went on to form MIPS Computer Systems, Inc. That company has morphed into the present-day MIPS Technologies, whose primary role is the design and subsequent licensing of MIPS architecture and cores.

The MIPS core has been licensed by many companies, several of which have become powerhouses in the embedded processor market. MIPS is a Reduced Instruction Set Computing (RISC) architecture with both 32-bit and 64-bit implementations shipping in many popular products. MIPS processors are found in a large variety of products, from high-end to consumer devices. It is public knowledge that MIPS processors power many popular well-known consumer products, such as Sony high definition television sets, Linksys wireless access points, and the popular Sony PlayStation 2 game console.^[6]

^[6] Source: www.mips.com/content/PressRoom/PressReleases/2003-12-22

The MIPS Technology website lists 73 licensees who are currently engaged in manufacturing products using MIPS processor cores. Some of these companies are household names, as with Sony, Texas Instruments, Cisco's Scientific Atlanta (a leading manufacturer of cable TV set-top boxes), Motorola, and others. Certainly, one of the largest and most successful of these is Broadcom Corporation.

3.2.5. Broadcom MIPS

Broadcom is a leading supplier of SOC solutions for markets such as cable TV set-top boxes, cable modems, HDTV, wireless networks, Gigabit Ethernet, and Voice over IP (VoIP). Broadcom's SOCs have been very popular in these markets. We mentioned earlier that you likely have Linux in your home even if you don't know it. Chances are, if you do, it is running on a Broadcom MIPS-based SOC.

In 2000, Broadcom acquired SiByte Inc., which resulted in the communications processor product lineup the company is currently marketing. These processors currently ship in single-core, dual-core, and quad-core configurations. The company still refers to them as SiByte processors.

The single-core SiByte processors include the BCM1122 and BCM1125H. They are both based on the MIPS64 core and operate at clock speeds at 400-900MHz. They include on-chip peripheral controllers such as DDR SDRAM controller, 10/100Mbps Ethernet, and PCI host controller. Both include SMBus serial configuration interface, PCMCIA, and two UARTs for serial port connections. The BCM1125H includes a triple-speed 10/100/1000Mbps Ethernet controller. One of the more striking features of these processors is their power dissipation. Both feature a 4W operating budget at 400MHz operation.

The dual-core SiByte processors include the BCM1250, BCM1255, and BCM1280. Also based on the MIPS64 core, these processors operate at clock rates from 600MHz (BCM1250) to as high as 1.2GHz (BCM1255 and BCM1280). These dual-core chips include integrated peripheral controllers such as DDR SDRAM controllers, various combinations of Gigabit Ethernet controllers, 64-bit PCI-X interfaces, and SMBus, PCMCIA, and multiple UART interfaces. Like their single-core cousins, these dual-core implementations also feature low power dissipation. For example, the BCM1255 features a 13W power budget at 1GHz operation.

The quad-core SiByte processors include the BCM1455 and BCM1480 communications processors. As with the other SiByte processors, these are based on the MIPS64 core. The cores can be run from 800MHz to 1.2GHz. These SOCs include integrated DDR SDRAM controllers, four separate Gigabit Ethernet MAC controllers, and 64-bit PCI-X host controllers, and also contain SMBus, PCMCIA, and four serial UARTs.

Table 3-7 summarizes select Broadcom SiByte processors.

Table 3-7. Broadcom Select SiByte Processor Highlights

Feature	BCM1125H	BCM1250	BCM1280	BCM1480
Core/speeds	SB-1	Dual SB-1	Dual SB-1	Quad SB-1
	MIPS64	MIPS64	MIPS64	MIPS64
	400-900MHz	600-1000MHz	800-1200MHz	800-1200MHz
DRAM controller	Y-DDR	Y-DDR	Y-DDR	Y-DDR
Serial interface	2-55Mbps	2-55Mbps	4 UART	4 UART
SMBus interface	2	2	2	2
PCMCIA	Y	Y	Y	Y
Gigabit Ethernet (10/100/1000Mbps)	2	3	4	4
PCI controller	Y	Y	Y PCI/PCI-X	Y PCI/PCI-X
Security engine	N	N	N
High-speed I/O (HyperTransport)	1	1	3	3

3.2.6. AMD MIPS

Advanced Micro Devices also plays a significant role in the embedded MIPS controller market. The company's 2002 acquisition of Alchemy Semiconductor garnered several popular single-chip integrated SOCs based on the MIPS32 core and architecture. The Alchemy line from AMD is based on the popular MIPS32 core. All feature relatively low power dissipation and a high level of onboard system integration.

The Au1000 and Au1100 operate at clock rates of 266-500MHz. Both feature onboard SDRAM controllers and separate bus controllers for attachment to external devices such as Flash and PCMCIA. Table 3-8 summarizes the current Alchemy product line.

Table 3-8. AMD Alchemy MIPS Highlights Summary

Feature[*]	Au1000	Au1100	Au1200	Au1500	Au1550
Core/speeds	MIPS32	MIPS32	MIPS32	MIPS32	MIPS32
	266-500MHz	333-500MHz	333-500MHz	333-500MHz	333-500MHz
DRAM controller	SDRAM	SDRAM	DDR SDRAM	SDRAM	DDR SDRAM
Ethernet 10/100	2	1		2	2
GPIO lines	32	48	48	39	43
UARTs	4	3	2	2	3
USB 1.1	Host + device	Host + device	USB 2.0	Host + device	Host + device
AC-97 audio	1	1	Via SPC	1	Via SPC
I2S controller	1	1	Via SPC		Via SPC
SD/MMC	N	2	2	N	N

^[*] Other peripherals include IrDA controller, LCD controller, 2 SPCs, Power management, DMA engine, RTC, Camera interface, LCD controller, h/w hardware acceleration of encryption/decryption, PCI host controller, 4 SPCs, and Security engine.

3.2.7. Other MIPS

As we pointed out earlier, nearly 100 current MIPS licensees are shown on the MIPS Technologies licensees web page, at www.mips.com/content/Licensees/ProductCatalog/licensees. Unfortunately, it is not possible in the space provided here to cover them all. Start your search at the MIPS technologies website for a good cross-section of the MIPS processor vendors.

For example, ATI Technologies uses a MIPS core in its Xilleon set-top box family of chipsets. Cavium Network's Octeon family uses MIPS64 cores in a variety of multicore processor implementations. Integrated Device Technology, Inc., (IDT) has a family of integrated communications processors called Interprise, based on the MIPS architecture. PMC-Sierra, NEC, Toshiba, and others have integrated processors based on MIPS. All of these and more are well supported under Linux.

3.2.8. ARM

The ARM architecture has achieved a very large market share in the consumer electronics marketplace. Many popular and now ubiquitous products contain ARM cores. Some well-known examples include the Sony PlayStation Portable (PSP), Apple iPod Nano,^[7] Nintendo Game Boy Micro and DS, TomTom GO 300 GPS, and the Motorola E680i Mobile Phone, which features embedded Linux. Processors containing ARM cores power a majority of the world's digital cellular phones, according to the ARM Corporate Backgrounder at www.arm.com/miscPDFs/3822.pdf.

^[7] Reported by ARM to be the top-selling toy during the Christmas 2005 shopping season in the United States.

The ARM architecture is developed by ARM Holdings, plc and licensed to semiconductor manufacturers around the globe. Many of the world's leading semiconductor companies have licensed ARM technology and are currently shipping integrated processors based on one of the several ARM cores.

3.2.9. TI ARM

Texas Instruments uses ARM cores in the OMAP family of integrated processors. These processors contain many integrated peripherals intended to be used as single-chip solutions for various consumer products, such as cellular handsets, PDAs, and similar multimedia platforms. In addition to the interfaces commonly found on integrated processors, such as UARTs and I²C, the OMAP devices contain a wide range of special-purpose interfaces, including the following:

• LCD screen and backlight controllers

• Buzzer driver

• Camera interface

• MMC/SD card controller

• Battery-management hardware

• USB client/host interfaces

• Radio modem interface logic

• Integrated 2D or 3D graphics accelerators

• Integrated security accelerator

• S-Video outputs

• IrDA controller

• DACs for direct TV (PAL/NTSC) video output

• Integrated DSPs for video and audio processing

Many popular cellular handsets and PDA devices have been marketed based on the TI OMAP platform. Because they are based on an ARM core, these processors are supported by Linux today. Table 3-9 compares some of the more recent members of the TI OMAP family.

Table 3-9. TI ARM OMAP Highlights Summary

Feature	OMAP1710	OMAP2420	OMAP2430	OMAP3430
Core/speeds	ARM926 TEJ	ARM11	ARM1136	ARM Cortex A8
	Up to 200MHz	330MHz	330MHz	550MHz
DRAM controller	Y	Y	Y	Y
UARTs	Y	Y	Y	Y
USB	Client + host	Client + host	Client + host	Client + host
I2C controller	Y	Y	Y	Y
MMC-SD interface	Y	Y	Y	Y
Keypad controller	Y	Y	Y	Y
Camera interface	Y	Y	Y	Y
Graphics accelerator	2D	2D/3D	2D/3D	Y
Integrated DSP	TM320C55x	TM320C55x	N	N
Video acceleration hardware	N	Imaging Video Accelerator (IVA)	Imaging Video Accelerator (IVA 2)	Imaging Video Accelerator (IVA 2 +)
Security accelerator	Y	Y	Y	Y
Audio codec support	Y	Y	Y	Y
Bluetooth & RF modem support interface	Y	Y	Y	Y
LCD controller	Y	Y	Y	Y
Display controllers	N	PAL/NTSC VGA/QVGA	PAL/NTSC VGA/QVGA	PAL/NTSC QVGA/XGA

3.2.10. Freescale ARM

The success of the ARM architecture is made more evident by the fact that leading manufacturers of competing architectures have licensed ARM technology. As a prime example, Freescale Semiconductor has licensed ARM technology for its line of i.MX application processors. These popular ARM-based integrated processors have achieved widespread industry success in multimedia consumer devices such as portable game platforms, PDAs, and cellular handsets.

The Freescale ARM product portfolio includes the i.MX21 and i.MX31 application processors. The i.MX21 features an ARM9 core, and the i.MX31 has an ARM11 core. Like their TI counterparts, these SOCs contain many integrated peripherals required by portable consumer electronics devices with multimedia requirements. The i.MX21/31 contain some of the following integrated interfaces:

• Graphics accelerator

• MPEG-4 encoder

• Keypad and LCD controllers

• Camera interface

• Audio multiplexer

• IrDA infrared I/O

• SD/MMC interface

• Numerous external I/O, such as PCMCIA, USB, DRAM controllers, and UARTs for serial port connection

3.2.11. Intel ARM XScale

Intel manufactures and markets several integrated processors based on the ARM v5TE architecture. Intel uses the XScale name for the architecture. These products are grouped into several application categories. Table 3-10 summarizes the XScale families by application type.

Table 3-10. Intel XScale Processor Summary

Category	Application	Example Processors
Application processors	Cellular handsets and PDAs	PXA27x, PXA29x
I/O processors	High-speed data processing used in storage, printing, telematics, and so on	IOP331/332/333
Network processors	Networking and communications data plane processing, fast packet processing, and so on	IXP425, IXP465 IXP2350, IXP2855

Many consumer and networking products have been developed using Intel XScale architecture processors. Some well-known examples include the GPS iQue M5 from Garmin, the iPAQ by Hewlett-Packard, smart phones from Palm (Treo) and Motorola (A760), and many others. Linux currently supports all these processors.

Intel's network processors are found in high-performance networking equipment where requirements exist for fast data-path processing. Examples include deep packet inspection, data encryption/decryption, packet filtering, and signal processing. These network processors each contain an ARM core coupled with one or more dedicated processing engines, called a network processing engine (NPE). These NPEs are dedicated to specific data-path manipulation in real time at wire speeds. The NPE is a microprocessor, in the sense that it can execute microcoded algorithms in parallel with the thread of execution in the ARM core. Refer to the Intel website, at www.intel.com, for additional information on this powerful family of integrated processors.

3.2.12. Other ARM

More than 100 semiconductor companies are developing integrated solutions based on ARM technologyfar too many to list here. Many offer specialized application processors serving vertical markets such as the handset market, storage area networking, network processing, and the automotive market, as well as many more. These companies include Altera, PMC-Sierra, Samsung Electronics, Philips Semiconductor, Fujitsu, and more. See the ARM Technologies website at www.arm.com for additional ARM licensees and information.

3.2.13. Other Architectures

We have covered the major architectures in widespread use in embedded Linux systems. However, for completeness, you should be aware of other architectures for which support exists in Linux. A recent Linux snapshot revealed 25 architecture branches (subdirectories). In some instances, the 64-bit implementation of an architecture is separated from its 32-bit counterpart. In other cases, ports are not current or are no longer maintained.

The Linux source tree contains ports for Sun Sparc and Sparc64, the Xtensa from Tensilica, and the v850 from NEC, to name a few. Spend a few minutes looking through the architecture branches of the Linux kernel to see the range of architectures for which Linux has been ported. Beware, however, that not all these architectures might be up-to-date in any given snapshot. You can be reasonably certain that the major architectures are fairly current, but the only way to be certain is to follow the development in the Linux community or consult with your favorite embedded Linux vendor. Appendix E, "Open Source Resources," contains a list of resources you can consult to help you stay current with Linux developments.