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30151-33 参数 Datasheet PDF下载

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型号: 30151-33
PDF下载: 下载PDF文件 查看货源
内容描述: 的Geode ™ GXM处理器与MMX支持集成的x86解决方案 [Geode⑩ GXm Processor Integrated x86 Solution with MMX Support]
分类和应用:
文件页数/大小: 244 页 / 4221 K
品牌: NSC [ National Semiconductor ]
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Architecture Overview (Continued)  
1.2 FLOATING POINT UNIT  
The FPU (Floating Point Unit) interfaces to the integer unit  
and the cache unit through a 64-bit bus. The FPU is x87-  
instruction-set compatible and adheres to the IEEE-754  
standard. Because almost all applications that contain  
FPU instructions also contain integer instructions, the  
GXm processor’s FPU achieves high performance by  
completing integer and FPU operations in parallel.  
other pending X-Bus memory requests to the SDRAM  
controller before completing.  
In addition, the internal bus interface unit provides config-  
uration control for up to 20 different regions within system  
memory with separate controls for read access, write  
access, cacheability, and PCI access.  
1.5 INTEGRATED FUNCTIONS  
FPU instructions are dispatched to the pipeline within the  
integer unit. The address calculation stage of the pipeline  
checks for memory management exceptions and  
accesses memory operands for use by the FPU. Once the  
instructions and operands have been provided to the FPU,  
the FPU completes instruction execution independently of  
the integer unit.  
The GXm processor integrates the following functions tra-  
ditionally implemented using external devices:  
High-performance 2D graphics accelerator  
Separate CRT and TFT data paths from the display  
controller  
SDRAM memory controller  
PCI bridge  
1.3 WRITE-BACK CACHE UNIT  
The 16 KB write-back unified cache is a data/instruction  
cache and is configured as four-way set associative. The  
cache stores up to 16 KB of code and data in 1024 cache  
lines.  
The processor has also been enhanced to support  
National Semiconductor’s proprietary Virtual System  
Architecture (VSA) implementation.  
The GXm processor implements a Unified Memory Archi-  
tecture (UMA). By using National Semiconductor’s Dis-  
play Compression Technology (DCT), the performance  
degradation inherent in traditional UMA systems is elimi-  
nated.  
The GXm processor provides the ability to allocate a por-  
tion of the L1 cache as a scratchpad, which is used to  
accelerate the Virtual Systems Architecture algorithms as  
well as for some graphics operations.  
1.4 MEMORY MANAGEMENT UNIT  
1.5.1 Graphics Accelerator  
The memory management unit (MMU) translates the lin-  
ear address supplied by the integer unit into a physical  
address to be used by the cache unit and the internal bus  
interface unit. Memory management procedures are x86-  
compatible, adhering to standard paging mechanisms.  
The graphics accelerator is a full-featured GUI (Graphical  
User Interface) accelerator. The graphics pipeline imple-  
ments a bitBLT engine for frame buffer bitBLTs and rect-  
angular fills. Additional instructions in the integer unit may  
be processed, as the bitBLT engine assists the CPU in the  
bitBLT operations that take place between system mem-  
ory and the frame buffer. This combination of hardware  
and software is used by the display driver to provide very  
fast transfers in both directions between system memory  
and the frame buffer. The bitBLT engine also draws ran-  
domly-oriented vectors, and scanlines for polygon fill. All  
of the pipeline operations described in the following list  
can be applied to any bitBLT operation.  
The MMU also contains a load/store unit that is responsi-  
ble for scheduling cache and external memory accesses.  
The load/store unit incorporates two performance-  
enhancing features:  
Load-store reordering that gives priority to memory  
reads required by the integer unit over writes to  
external memory.  
Pattern Memory. Render with 8x8 dither, 8x8 mono-  
chrome, or 8x1 color pattern.  
Memory-read bypassing that eliminates unnecessary  
memory reads by using valid data from the execution  
unit.  
Color Expansion. Expand monochrome bitmaps to  
full-depth 8- or 16-bit colors.  
1.4.1 Internal Bus Interface Unit  
The internal bus interface unit provides a bridge from the  
GXm processor to the integrated system functions (i.e.,  
memory subsystem, display controller, graphics pipeline)  
and the PCI bus interface.  
Transparency. Suppresses drawing of background  
pixels for transparent text.  
Raster Operations. Boolean operation combines  
source, destination, and pattern bitmaps.  
When external memory access is required, the physical  
address is calculated by the memory management unit  
and then passed to the internal bus interface unit, which  
translates the cycle to an X-Bus cycle (the X-Bus is a  
National Semiconductor proprietary internal bus which  
provides a common interface for all of the system mod-  
ules). The X-Bus memory cycle now is arbitrated between  
Revision 3.1  
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