Specifications
Intel
®
Quark SoC X1000 Core
October 2013 Developer’s Manual
Order Number: 329679-001US 309
Feature Determination—Intel
®
Quark Core
Appendix C Feature Determination
C.1 CPUID Instruction
CPUID instruction returns processor identification and feature information in the EAX,
EBX, ECX, and EDX registers. The instruction's output values are dependent on the
contents of the EAX register upon execution. Table 102 summarizes the information
returned depending on the initial value loaded into EAX register.
CPUID returns 0 for leaves greater than 0x02 but less than 0x07 (the highest basic
leaf) as stated in the [Intel Arch SDM]: "If a value entered for CPUID.EAX is less than
or equal to the maximum input value and the leaf is not supported on the processor
then 0 is returned in all registers."
Furthermore, CPUID returns values corresponding to leaf 0x01 for all other EAX values
not listed in the table, as stated in the [Intel Arch SDM]: "If a value entered for
CPUID.EAX is higher than the maximum input value for basic or extended function for
that processor then the data for the highest basic information leaf is returned."
Note that zeroes are currently returned for the Processor Brand String (leaf
0x8000002-0x80000004).
Table 102. CPUID with PAE/XD/SMEP features implemented (Sheet 1 of 2)
EAX value Register Return value Information provided about the processor
0x2
EAX
EBX,ECX,EDX
0x00000001
0x0
No cache information to report
0x3-0x6
EAX,EBX,
ECX,EDX
0x0
0x7
†
& ECX=0 EAX 0x1 Maximum number of supported leaf 7 sub-leaves
EBX 0x80 or 0x0 Bit 7: SMEP (Returns if SMEP is enabled)
ECX,EDX 0x0
0x7 & ECX!=0 EAX=EBX=ECX=EDX=All 0's
0X80000000 EAX 0x80000008 Maximum input value for extended function CPUID leaf
EBX,ECX,EDX 0x0
0X80000001 EAX,EBX,ECX 0x0
EDX 0x100000
Bit 20: execute disable bit available if the
IA32_MISC_ENABLES[34]=0; If IA32_MISC_ENABLES[34]=1
EDX[20]=1'b0
† When the value of Limit CPUID Maxval (bit 22 of IA32_MISC_ENABLE) is set to 1, all basic leaves above 3 should be
invisible. In this case, leaf 7 returns all zeros.