
12
AMD-K5 Processor
AMD K86 Family BIOS and Software Tools Developers Guide
21062E/0—June 1997
Preliminary Information
SMM Revision Identifier
The SMM revision identifier at offset FEFCh in the SMM
state-save area specifies the version of SMM and the extensions
available on the processor. The SMM revision identifier fields,
shown in Table 5, are as follows:
I
Bits 31–18
—
reserved
Bit 17
—SMM base address relocation (always 1 = enabled)
Bit 16
—I/O trap restart (always 1 = enabled)
Bits 15–0
—SMM revision level = 0000
I
I
I
Note:
The I/O trap restart and the SMM base address relocation
functions are always enabled in the AMD-K5 processor and
do not need to be specifically enabled.
SMM Base Address
During RESET, the processor sets the code-segment (CS) base
address for the SMM memory area—the SMM base address—
to its default, 0003_0000h. The SMM base address at offset
FEF8h in the SMM state-save area can be changed by the SMM
service routine to any address aligned to a 32-Kbyte boundary.
(Locations not aligned to a 32-Kbyte boundary cause the
processor to enter the Shutdown state when executing the RSM
instruction.)
In some operating environments it may be desirable to relocate
the 64-Kbyte SMM memory area to a high memory area to
provide more low memory for legacy software. During system
initialization, the base of the 64-Kbyte SMM memory area is
relocated by the BIOS. To relocate the SMM base address, the
system enters the SMM handler at the default address. This
handler changes the SMM base address location in the SMM
state-save area, copies the SMM handler to the new location,
and exits SMM.
Table 5.
SMM Revision Identifier Fields
Bits 31–18
Reserved
0
Bit 17
Bit 16
Bits 15–0
SMM Revision Level
0000
SMM Base Relocation
1
I/O Trap Extension
1