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656 AMD Geode™ LX Processors Data Book
Instruction Set
33234H
8.3.4.12 SVDC - Save Segment Register and Descriptor
Operation
Description
Write the specified segment descriptor (either DS, ES, FS, GS, SS, or CS) to memory. Below is the format of the descriptor
contents in memory.
Flags Affected
None.
Exceptions
#UD If current privilege level is not 0, or the SMM_INST_EN = 0 and if the processor is not in SMM and if the processor
is not in DMM.
Notes
The reg field within the mod r/m byte specifies which segment’s register and descriptor should be written. Reg fields of 0,
1, 2, 3, 4, and 5 specify the ES, CS, SS, DS, FS, and GS selectors respectively. The RSDC instruction is not recognized if
the reg field is 6 or 7.
8.3.4.13 SVLDT - Save Local Descriptor Table Register and Descriptor
Operation
Description
Write the Local Descriptor Table register and descriptor to memory. Below is the format of the descriptor contents in mem-
ory.
Flags Affected
None.
Opcode Instruction Clocks Description
0F 78 /r SVDC sr, m80 7 Restore descriptor from memory
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
SELECTOR[15:3] TI RPL +8
BASE[31:24] G B
0 V LIMIT[19:16] 1 DPL 1 0 E W A BASE[23:16] +4
BASE[15:0] LIMIT[15:0] +0
Opcode Instruction Clocks Description
0F 7A SVLDT m80 7 Save LDT to memory
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
SELECTOR[15:3] TI RPL +8
BASE[31:24] G B
0 V LIMIT[19:16] 1 DPL 1 0 E W A BASE[23:16] +4
BASE[15:0] LIMIT[15:0] +0
IF (CPL<>0 OR (SMM_INST_EN=0 AND SMM=0 AND DMM=0))
#UD;
ELSE
MEM80 <= SEG.DESCR;
IF (CPL<>0 OR (SMM_INST_EN=0 AND SMM=0 AND DMM=0))
#UD;
ELSE
MEM80 <= LDT.DESCR;