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30036-23 参数 Datasheet PDF下载

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型号: 30036-23
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内容描述: 的Geode ™ GXLV处理器系列的低功耗X86集成解决方案 [Geode⑩ GXLV Processor Series Low Power Integrated x86 Solutions]
分类和应用:
文件页数/大小: 247 页 / 4117 K
品牌: NSC [ National Semiconductor ]
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Processor Programming (Continued)  
3.5.4 Paging Mechanism  
CR3 control register, also referred to as the Page Direc-  
tory Base Register (PDBR).  
The paging mechanism translates a linear address to its  
corresponding physical address. If the required page is  
not currently present in RAM, an exception is generated.  
When the operating system services the exception, the  
required page can be loaded into memory and the instruc-  
tion restarted. Pages are either 4 KB or 1 MB in size. The  
CPU defaults to 4 KB pages that are aligned to 4 KB  
boundaries.  
Bits [21:12] of the 32-bit linear address, referred to as the  
Page Table Index (PTI), locate a 32-bit entry in the sec-  
ond-level page table. This page table entry (PTE) contains  
the base address of the desired page frame. The second-  
level page table addresses up to 1K individual page  
frames. A second-level page table is 4 KB in size and is  
itself a page. Bits [11:0] of the 32-bit linear address, the  
Page Frame Offset (PFO), locate the desired physical  
data within the page frame.  
A page is addressed by using two levels of tables as illus-  
trated in Figure 3-8. Bits [31:22] of the 32-bit linear  
address, the Directory Table Index (DTI), are used to  
locate an entry in the page directory table. The page  
directory table acts as a 32-bit master index to up to 1 KB  
individual second-level page tables. The selected entry in  
the page directory table, referred to as the directory table  
entry (DTE), identifies the starting address of the second-  
level page table. The page directory table itself is a page  
and is therefore aligned to a 4 KB boundary. The physical  
address of the current page directory table is stored in the  
Since the page directory table can point to 1 KB page  
tables, and each page table can point to 1 KB page  
frames, a total of 1 MB page frames can be implemented.  
Each page frame contains 4 KB, therefore, up to 4 GB of  
virtual memory can be addressed by the CPU with a sin-  
gle page directory table.  
Linear  
Address  
31  
22 21  
12 11  
0
Directory Table Index  
(DTI)  
Page Table Index  
(PTI)  
Page Frame Offset  
(PFO)  
4 GB  
31  
0
1
0
Main TLB  
32-Entry  
4-Way Set  
Associative  
DTE Cache  
2-Entry  
Fully Associative  
-4 KB  
4 KB  
4 KB  
Physical Page  
Memory  
DTE  
PTE  
-0  
0
CR3  
0
0
Control  
Register  
Directory Table  
Page Table  
External Memory  
Figure 3-8. Paging Mechanism  
Revision 1.1  
77  
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