CPUID
| CPUID | |
| CPU Identification | |
| Usage: | {{{Usage}}} |
|---|---|
| Usage: | {{{Usage2}}} |
| Modifies Flags: | None |
| Availability: | Pentium |
The CPUID instruction can be used to retrieve various amount of information about your cpu, like its vendor string and model number, the size of internal caches and (more interesting), the list of CPU features supported.
How to use CPUID
Note that prior to use the CPUID instruction, you should also make sure the processor support it by testing the 'ID' bit in eflags (this is 0x200000 and is modifiable only when CPUID instruction is supported. For systems that doesn't support CPUID, writing a '1' at that place will have no effect)
CPU Brand
When called with EAX = 0, CPUID returns the brand name in EBX, EDX and ECX. Writing these to memory in this order results in a 12-character string. These can be tested against known brands:
Also, EAX is set to the maximum EAX value supported for CPUID calls, as not all queries are supported on all processors
CPU Features
When called with EAX = 1 (CPUID_GETFEATURES), CPUID returns a bit field in EDX containing the following values. Note that different brands of CPUs may have given different meanings to these. Recent processors also use ECX for features (which form a different set), with which you should be very careful as some old CPUs return bogus information in this register.
Using CPUID from GCC
CPUID can be invoked with various request codes (in eax) and will return values in general registers (much as a built-in service interrupt). The following code is made Public Domain out of Clicker's x86/cpu.h
Links
- You can check out SandPile.org for an exhaustive list of functions available through CPUID instruction.
- CPUID For OS Developers, an implementation written by Brynet-Inc.
- Forum topic about issues with CPUID