Книга: Embedded Linux Primer: A Practical, Real-World Approach

3.1.4. Companion Chipsets

3.1.4. Companion Chipsets

Stand-alone processors such as those just described require support logic to connect to and enable external peripheral devices such as main system memory (DRAM), ROM or Flash memory, system busses such as PCI, and other peripherals, such as keyboard controllers, serial ports, IDE interfaces, and the like. This support logic is often accomplished by companion chipsets, which may even be purpose-designed specifically for a family of processors.

For example, the Pentium M is supported by one such chipset, called the 855GM. The 855GM chipset is the primary interface to graphics and memorythus, the suffix-GM. The 855GM has been optimized as a companion to the Pentium M. Figure 3-1 illustrates the relationship between the processor and chipsets in this type of hardware design.

Figure 3-1. Processor/chipset relationship

Note the terminology that has become common for describing these chipsets. The Intel 855GM is an example of what is commonly referred to as a northbridge chip because it is directly connected to the processor's high-speed front side bus (FSB). Another companion chip that provides I/O and PCI bus connectivity is similarly referred to as the southbridge chip because of its position in the architecture. The southbridge chip (actually, an I/O controller) in these hardware architectures is responsible for providing interfaces such as those shown in Figure 3-1, including Ethernet, USB, IDE, audio, keyboard, and mouse controllers.

On the PowerPC side, the Tundra Tsi110 Host Bridge for PowerPC is an example of a chipset that supports the stand-alone PowerPC processors. The Tsi110 supports several interface functions for many common stand-alone PowerPC processors. The Tundra chip supports the Freescale MPC74xx and the IBM PPC 750xx family of processors. The Tundra chip can be used by these processors to provide direct interfaces to the following peripherals:

• DDR DRAM, integrated memory controller

• Ethernet (the Tundra provides four gigabit Ethernet ports)

• PCI Express (supports 2 PCI Express ports)

• PCI/X (PCI 2.3, PCI-X, and Compact PCI [cPCI])

• Serial ports

• I2C

• Programmable interrupt controller

• Parallel port

Many manufacturers of chipsets exist, including VIA Technologies, Marvell, Tundra, nVidia, Intel, and others. Marvell and Tundra primarily serve the PowerPC market, whereas the others specialize in Intel architectures. Hardware designs based on one of the many stand-alone processors, such as Intel x86, IBM, or Freescale PowerPC, need to have a companion chipset to interface to system devices.

One of the advantages of Linux as an embedded OS is rapid support of new chipsets. Linux currently has support for those chipsets mentioned here, as well as many others. Consult the Linux source code and configuration utility for information on your chosen chipset.

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