AMD-X5-133ADW AMD [Advanced Micro Devices], AMD-X5-133ADW Datasheet - Page 47

• Manufacturer Part Number: AMD-X5-133ADW
• Manufacturer: AMD [Advanced Micro Devices]

7.7.3 Auto HALT Restart
The Auto HALT Restart slot at register offset (word lo-
cation) 7F02h in SMRAM indicates to the SMI handler
that the SMI interrupted the CPU during a HALT state;
bit 0 of slot 7F02h is set to 1 if the previous instruction
was a HALT (see Figure 28). If the SMI did not interrupt
the CPU in a HALT state, then the SMI microcode sets
bit 0 of the Auto HALT Restart slot to 0. If the previous
instruction was a HALT, the SMI handler can choose to
either set or reset bit 0. If this bit is set to 1, the RSM
microcode execution forces the processor to re-enter
the HALT state. If this bit is set to 0 when the RSM
instruction is executed, the processor continues execu-
tion with the instruction just after the interrupted HALT
instruction. If the HALT instruction is restarted, the CPU
will generate a memory access to fetch the HALT in-
struction (if it is not in the internal cache), and execute
a HALT bus cycle.
Table 15 shows the possible restart configurations. If
the interrupted instruction was not a HALT instruction
(bit 0 is set to 0 in the Auto HALT Restart slot upon SMM
entry), setting bit 0 to 1 will cause unpredictable behavior
when the RSM instruction is executed.
7.7.4 I/O Trap Restart
The I/O instruction restart slot (register offset 7F00h in
SMRAM) gives the SMI handler the option of causing
the RSM instruction to automatically re-execute the in-
terrupted I/O instruction (see Figure 29).
Value at
Entry
15
Figure 28. Auto HALT Restart Register Offset
Table 15. HALT Auto Restart Configuration
0
0
1
1
Reserved
at Exit
Value
0
1
0
1
Return to next instruction in interrupted
program
Unpredictable
Returns to instruction after HALT
Returns to interrupted HALT instruction
Processor Action on Exit
1
0
Register Offset 7F02h
HALT Auto Restart
Am5
X
PRELIMINARY
86 Microprocessor
.
When the RSM instruction is executed — if the I/O in-
struction restart slot contains the value 0FFh — the CPU
automatically re-executes the l/O instruction that the
SMI signal trapped. If the I/O instruction restart slot con-
tains the value 00h when the RSM instruction is execut-
ed, then the CPU does not re-execute the I/O instruction.
The CPU automatically initializes the I/O instruction re-
start slot to 00h during SMM entry. The I/O instruction
restart slot should be written only when the processor
has generated an SMI on an I/O instruction boundary.
Processor operation is unpredictable when the I/O in-
struction restart slot is set when the processor is servic-
ing an SMI that originated on a non-I/O instruction
boundary.
If the system executes back-to-back SMI requests, the
second SMI handler must not set the I/O instruction re-
start slot. The second back-to-back SMI signal will not
have the I/O Trap Word set.
7.7.5 I/O Trap Word
The I/O Trap Word contains the address of the I/O ac-
cess that forced the external chipset to assert SMI,
whether it was a read or write access, and whether the
instruction that caused the access to the I/O address
was a valid I/O instruction. Table 16 shows the layout.
Bits 31–16 contain the I/O address that was being ac-
cessed at the time SMI became active. Bits 15–2 are
reserved.
If the instruction that caused the I/O trap to occur was
a valid I/O instruction (IN, OUT, INS, OUTS, REP INS,
or REP OUTS), the Valid I/O Instruction bit is set. If it
was not a valid I/O instruction, the bit is saved as a 0.
For REP instructions, the external chip set should return
a valid SMI within the first access.
Bit 0 indicates whether the opcode that was accessing
the I/O location was performing either a read (1) or a
write (0) operation as indicated by the R/W bit.
I/O Address
Figure 29. I/O Instruction Restart Register Offset
31–16
15
Table 16. I/O Trap Word Configuration
Reserved
15–2
I/O instruction restart slot
Valid I/O Instruction
0
Register offset 7F00h
1
AMD
R/W
0
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