AMD-K6-2ESLASH400AMZ datasheet(242/332 Pages) AMD

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224

System Management Mode (SMM)

Chapter 11

AMD-K6™-2E Processor Data Sheet

22529B/0—January 2000

Preliminary Information

Table 43 shows the format of the I/O trap doubleword.

The I/O trap doubleword is related to the I/O trap restart slot

(see “I/O Trap Restart Slot” on page 224). If bit 1 of the I/O

trap doubleword is set by the processor, it means that SMI#

was asserted during the execution of an I/O instruction. The

SMI handler tests bit 1 to see if there is a valid I/O instruction

trapped. If the I/O instruction is valid, the SMI handler is

required to ensure the I/O trap restart slot is set properly. The

I/O trap restart slot informs the CPU whether it should

re-execute the I/O instruction after the RSM or execute the

instruction following the trapped I/O instruction.

Note: If SMI# is sampled asserted during an I/O bus cycle a mini-

mum of three clock edges before BRDY# is sampled asserted,

the associated I/O instruction is guaranteed to be trapped by

the SMI handler.

11.7

I/O Trap Restart Slot

The I/O trap restart slot at offset FF00h in the SMM state-save

area specifies whether the trapped I/O instruction should be

re-executed on return from SMM. This slot in the state-save area

is called the I/O instruction restart function. Re-executing a

trapped I/O instruction is useful, for example, if an I/O write

occurs to a disk that is powered down. The system logic

monitoring such an access can assert SMI#. Then the SMM

service routine would query the system logic, detect a failed I/O

write, take action to power-up the I/O device, enable the I/O

trap restart slot feature, and return from SMM.

The fields of the I/O trap restart slot are defined as follows:

Bits 31–16—Reserved

Bits 15–0—I/O instruction restart on return from SMM:

0000h

= execute the next instruction after the trapped

I/O instruction

00FFh = re-execute the trapped I/O instruction

Table 43. I/O Trap Doubleword Configuration

31—16

15—4

I/O Port

Address

Reserved

REP String

Operation

I/O String

Operation

Valid I/O

Instruction

Input or

Output

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