AMD AMD-K6-2/450 Design Guide - Page 25
System Management Mode (SMM), StateSave Map Differences, I/O Trap Dword Differences - data sheet
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23913A/0-November 2000 Preliminary Information Embedded AMD-K6™ Processors BIOS Design Guide System Management Mode (SMM) This section documents the System Management Mode (SMM) differences between specified models of the AMD-K6 processor and the Pentium processor. For more information on SMM implementation in the K86 processors, see the appropriate AMD-K6 or AMD-K6E processor data sheet. State-Save Map Differences The SMM implemented in the AMD-K6 processor differs from the SMM implemented in the Pentium® processor in one way. The Interrupt Descriptor Table (IDT) base location in the AMD-K6 processors is located at offset FF90h. The Pentium processor has the IDT base located at offset FF94h. I/O Trap Dword Differences The I/O trap dword is located at offset FFA4h. Its AMD-K6 processor bit fields are shown in Table 6. This state-save area, which is reserved in Pentium processors, contains information regarding an I/O instruction that may have been trapped by an SMI# assertion. Table 6. AMD-K6™ Processor I/O Trap Dword Configuration at Offset FFA4h Bits 31-16 Bits 15-4 I/O Port Address Reserved Bit 3 Bit 2 Rep String Operation I/O String Operation Bit 1 Valid I/O Instruction Bit 0 Input or Output System Management Mode (SMM) 13