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| 型号： | Enhanced Am486 dx4 |
| 厂商： | Advanced Micro Devices, Inc. |
| 英文描述： | High-Performance Design On-Chip Integration Complete 32-Bit Architecture Micrprocessor(高性能设计片上集成完全32位体系微处理器) |
| 中文描述： | 高性能设计的片上集成完整的32位架构Micrprocessor（高性能设计片上集成完全32位体系微处理器） |
| 文件页数： | 47/69页 |
| 文件大小： | 1068K |
| 代理商： | ENHANCED AM486 DX4 |
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Enhanced Am486 Microprocessor
AMD
47
PRELIMINARY
7.7.3
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
micro code 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.
Auto HALT Restart
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 behav-
ior when the RSM instruction is executed
7.7.4
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 interrupted
I/O instruction (see Figure 29).
I/O Trap Restart
Table 15. HALT Auto Restart Configuration
Value at
Entry
Value
at Exit
Processor Action on Exit
0
0
Return to next instruction in interrupted
program
0
1
Unpredictable
1
0
Returns to instruction after HALT
1
1
Returns to interrupted HALT instruction
HALT Auto Restart
Register Offset 7F02h
Reserved
15
1
0
Figure 28. Auto HALT Restart Register Offset
.
When the RSM instruction is executed, if the I/O instruction
re-start slot contains the value 0FFh, then the CPU automat-
ically re-executes the l/O instruction that the SMI signal
trapped. If the I/O instruction restart slot contains the value 00h
when the RSM instruction is executed, then the CPU does
not re-execute the I/O instruction. The CPU automatically
initializes the I/O instruction restart 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 instruc-
tion boundary. Processor operation is unpredictable when the
I/O instruction restart slot is set when the processor is servicing
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
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.
I/O Trap Word
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.
If an SMI occurs and it does not trap an I/O instruction,
the contents of the I/O address and R/W bit are unpre-
dictable and should not be used.
Table 16. I/O Trap Word Configuration
31–16
15–2
1
0
I/O Address
Reserved
Valid I/O Instruction
R/W
15
0
I/O instruction restart slot
Register offset 7F00h
Figure 29. I/O Instruction Restart Register Offset
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