====== CPUID settings ======

===== Name =====

    CPUID_SETTINGS

===== Header file =====

Configured via ''[[http://git.ipxe.org/ipxe.git/blob/HEAD:/src/config/settings.h|config/settings.h]]''.

===== Examples =====

=== Enable CPUID settings ===

    #define CPUID_SETTINGS        /* CPUID settings */

===== Description =====

This build option enables support for the CPUID settings, which expose information retrieved using the [[https://en.wikipedia.org/wiki/CPUID|CPUID]] instruction.

The CPU vendor and model can be retrieved using the ''[[:cfg:cpuvendor]]'' and ''[[:cfg:cpumodel]]'' settings.

Other information can be retrieved by constructing a numbered setting using the syntax ''${cpuid/<register>.<function>}}'', where ''<function>'' is the CPUID function number and ''<register>'' indicates the CPU register in which the information is returned (encoded as ''%eax=0'', ''%ebx=1'', ''%ecx=2'', ''%edx=3'').  For example ''${cpuid/2.0x80000001}'' will give the value of ''%ecx'' after calling CPUID with ''%eax=0x80000001''.

For some CPUID leaves (such as ''%eax=0x00000004''), there is also a subfunction number.  This may be specified using the syntax ''${cpuid/<subfunction>.0x40.<register>.<function>}''.

===== See also =====

  * ''[[:cfg:cpumodel]]'' setting
  * ''[[:cfg:cpuvendor]]'' setting
  * ''[[:cmd:cpuid]]'' command
  * [[:buildcfg|List of all iPXE build options]]