Christopher Hallinan - Embedded Linux Primer - A Practical, Real-World Approach

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 I 2C, 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

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

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

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.

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.

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.