AMD AMD-K6-2/400 User Guide - Page 70
SYSCALL/SYSRET, Target Address, Register STAR, Write Handling, Control Register
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Preliminary Information AMD-K6™-2E+ Embedded Processor Data Sheet 23542A/0-September 2000 SYSCALL/SYSRET Target Address Register (STAR) The SYSCALL/SYSRET target address register (STAR) contains the target EIP address used by the SYSCALL instruction and the 16-bit code and stack segment selector bases used by the SYSCALL and SYSRET instructions. Figure 35 shows the format of the STAR register, and Table 7 defines the function of each bit of the STAR register. For more information, see the SYSCALL and SYSRET Instruction Specification Application Note, order# 21086. The STAR register is MSR C000_0081h. 63 48 47 32 31 SYSRET CS Selector and SS Selector Base SYSCALL CS Selector and SS Selector Base 0 Target EIP Address Figure 35. SYSCALL/SYSRET Target Address Register (STAR) Table 7. SYSCALL/SYSRET Target Address Register (STAR) Definition Bit Description R/W 63-48 SYSRET CS and SS Selector Base R/W 47-32 SYSCALL CS and SS Selector Base R/W 31-0 Target EIP Address R/W Write Handling Control Register (WHCR) 63 The Write Handling Control Register (WHCR) is a MSR that contains two fields -the Write Allocate Enable Limit (WAELIM) field, and the Write Allocate Enable 15-to-16-Mbyte (WAE15M) bit (see Figure 36). For more information, see "Write Allocate" on page 215. The WHCR register is MSR C000_0082h. 32 31 22 21 17 16 15 0 W A WAELIM E 1 5 M Reserved Symbol WAELIM WAE15M Description Bits Write Allocate Enable Limit 31-22 Write Allocate Enable 15-to-16-Mbyte 16 Note: Hardware RESET initializes this MSR to all zeros. Figure 36. Write Handling Control Register (WHCR) 48 Software Environment Chapter 3