AMD AMD-K6-2/450 Design Guide - Page 84

Preliminary Information Embedded AMD-K6™ Processors BIOS Design Guide 23913A/0-November 2000 Standard Functions Function 0 - Largest Standard Function Input Value and Vendor Identification String Input: EAX = 0 Output: EAX = Largest function input value recognized by the CPUID instruction EBX, EDX, ECX = Vendor identification string This is a standard function found in all processors implementing the CPUID instruction. It returns two values. The first value is returned in the EAX register and indicates the largest standard function value recognized by the processor. The second value is the vendor identification string. This 12-character ASCII string is returned in the EBX, EDX, and ECX registers in little-endian format. AMD processors return a vendor identification string of "AuthenticAMD" as follows: EBX h t uA 68 74 75 41 EDX i tne 69 74 6E 65 ECX DMA c 44 4D 41 63 Software uses the vendor identification string as follows: s To identify the processor as an AMD processor s To apply AMD's definition of the CPUID instruction for all additional function calls Function 1 - Processor Signature and Standard Feature Flags Input: EAX = 1 Output: EAX = Processor Signature EBX = Reserved ECX = Reserved EDX = Standard Feature Flags Function 1 returns two values - the Processor Signature and the Standard Feature Flags. The processor signature is returned in the EAX register and identifies the specific processor by providing information on its type -instruction family, model, and revision (stepping). The information is formatted as follows: s EAX[3-0] Stepping ID s EAX[7-4] Model s EAX[11-8] Instruction Family s EAX[31-12] Reserved 72 Appendix A