AMD AMD5K86 - Halt Restart Slot

1 8524B/O-Mar1996
AMD~
AMD5~6 Processor Technical Reference Manual
If the SMM base address is rewritten, the processor saves its
state at the new base address the next time SMM is entered,
and each time thereafter, until RESET. The relocated
addresses for the SMM memory will then be as follows:
• SMM base address-Default: 0003_0000h. Relocated: offset
FEF8 in the SMM state-save area (see Table 6-2)
• Service Routine Entry Point-SMM base address + 8000h
• Top-SMM base address + FFFFh
This SMM base address relocation feature is compatible with
the Pentium processor's analogous feature. The following
pseudo-code implements a relocatable SMM base address in
BIOS:
begin
{
if SMI Handler is to be Relocated then
{
set SMM Base Address (offset FEF8h) to new value
resume
}
else
{
end
SMM execution to begin at relocation area.
resume
}
To relocate the SMM base address above the 1-Mbyte limit
imposed by Real-mode segment addressing, use the address-
override prefix to generate the offset in 32-bit registers. If the
SMM base address is relocated to a block below 16 Mbytes,
data in the DS segment (which has a segment base of
OOOO_OOOOh) can be accessed by the following code:
mov ebx,OOFExxxxh; 64K segment from OOFE_OOOOh to OOFE_FFFFh
mov ax, ds:[ebx]
System Management Mode (SMM)
6-29