Geode GXLV Processor Series Low Power Integrated x86 Solutions

Geode GXLV Processor SeriesProcessor Programming (Continued)Table 3-22. Descriptors Bit DefinitionsBitMemoryOffset Name Description31:24 +4 BASE Segment Base Address: Three fields which collectively define the base location for the segment in7:0 +44 GB physical address space.31:16 +019:16 +4 LIMIT Segment Limit: Two fields that define the size of the segment based on the Segment Limit15:0 +0Granularity Bit.If G = 1: Limit value interpreted in units of 4 KB.If G = 0: Limit value is interpreted in bytes.23 +4 G Segment Limit Granularity Bit: Defines LIMIT multiplier.If G = 1: Limit value interpreted in units of 4 KB. Segment size ranges from 4 KB to 4 GB.If G = 0: Limit value is interpreted in bytes. Segment size ranges from 1 byte to 1 MB.22 +4 D Default Length for Operands and Effective Addresses:If D = 1: Code segment = 32-bit length for operands and effective addresses.If D = 0: Code segment = 16-bit length for operands and effective addresses.If D = 1: Data segment = Pushes, calls and pop instructions use 32-bit ESP register.If D = 0: Data segment = Stack operations use 16-bit SP register.20 +4 AVL Segment Available: This field is available for use by system software.15 +4 P Segment Present:If = 1: Segment is memory segment allocated.If = 0: The BASE and LIMIT fields become available for use by the system. Also, If = 0, a segmentnot-presentexception generated when selector for the descriptor is loaded into a segment registerallowing virtual memory management.14:13 +4 DPL Descriptor Privilege Level:If = 00: Highest privilege levelIf = 11: Lowest privilege level12 +4 S Descriptor Type:If = 1: Code or data segmentIf = 0: System segment11:8 +4 TYPE Segment Type: Refer to Table 3-23 for TYPE bit definitions.Bit 11 = ExecutableBit 10 = Conforming if Bit 12 = 1Bit 10 = Expand Down if Bit 12 = 0Bit 9 = Readable, if Bit 12 = 1Bit 9 = Writable, if Bit 12 = 0Bit 8 = Accessedwww.national.com 72 Revision 1.3