DSP 104-plus, Справочное руководство

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158004.B00 13
2 PROCESSOR AND MEMORY
The TP400 single board computer is based around the National Semiconductor
Geode GX1 chip set. There is one SODIMM SDRAM socket. The standard TP400 is
supplied without memory, allowing you to choose memory to suit your application.
SDRAM options are detailed in Appendix D, Options and Ordering Information.
2.1 PROCESSOR
The TP400 is based on the National Semiconductor Geode GX1 chip set. This is a
highly integrated chip set that includes a Pentium-class MMX-Enhanced x86
compatible processor and many integrated peripherals. It includes all of the
motherboard support circuits used in PCs as well as graphics and audio circuitry.
The Geode GX1 is a 320-pin pin-grid array (PGA) chip that is visible on the top side
of the TP400. The processor is socketed, allowing different speed-grade processors
to be fitted. The Geode GX1 is available at a variety of speed grades, up to 300MHz.
A 300MHz processor is fitted as standard, although it may be run at slower clock
speeds to reduce power consumption. A heatsink or fan can be fitted to the
processor, and a connector close to the processor provides power to the fan.
Although the Geode GX1 runs much cooler than equivalent Pentium processors,
some heatsink or fan is likely to be required in most applications.
DSP Design can supply a passive heatsink, and a heatsink/fan combination. See
Appendix D for ordering information.
The Geode GX1 also integrates a high-performance graphics engine. This provides
VGA-compatible graphics as well as adding high-performance 2D graphics
accelerator logic that is driven by operating system-specific drivers. To provide a high
level of system integration, improve performance and reduce system costs, the
graphics engine uses a portion of the system SDRAM memory as graphics memory.
This is referred to as unified memory architecture (UMA).
So as to stop the graphics sub-system from using too much of the memory
bandwidth, the Geode GX1 implements graphics compression and caching circuitry.
Under this scheme, graphics data is read from the graphics memory, compressed,
and written back to a separate graphics cache memory. From then on, and until that
line of the display is changed, it is the compressed data that is read from the cache
and displayed, rather than the full uncompressed graphics data.
The graphics compression and caching scheme, together with the fact that the
processor, graphics engine and SDRAM interface are closely coupled, results in a
very high level of graphics performance.
As a compromise, not all of the legacy VGA registers are implemented in hardware.
Some registers are emulated by an SMI interrupt. National Semiconductor refers to
this as VSA - Virtual System Architecture. The VSA code is also responsible for the
SoundBlaster-compatible audio and some power management features. This
software emulation of hardware can give rise to some problems, which are described
in section 3.10.
The companion chip to the Geode GX1 processor is the CS5530A. This is the BGA