Intel 386 CLOCK AND POWER MANAGEMENT UNIT, 8.1.2.3 Watchdog Timer Unit Operation During Idle Mode

8-5
CLOCK AND POWER MANAGEMENT UNIT
Figure 8-3. SMM Interaction with Idle and Powerdown Modes
8.1.2.2 Bus Interface Unit Operation During Idle Mode
The bus interface unit (BIU) can process DMA, DRAM refresh, and external hold requests during
idle mode. When the first request occurs, the core wakes up long enough to relinquish bus control
to the bus arbiter, then returns to idle mode. For the remaining time in idle mode, the bus arbiter
controls the bus. DMA, DRAM refresh, and external hold requests are processed in the same way
as during normal operation.
8.1.2.3 Watchdog Timer Unit Operation During Idle Mode
When the watchdog timer unit is in system watchdog mode, idle mode stops the down-counter.
Since no software can run while the CPU is idle, a software watchdog is not needed. When it is
in bus monitor or general-purpose timer mode, the watchdog timer unit continues to run while the
device is in idle mode. (Chapter 17 describes the watchdog timer unit.)
Reset or
RSM Instruction
with Halt Restart
Slot Clear
System
Management
Mode
Powerdown
Mode Idle Mode
Normal
Operation
SMI#
A2229-03
Halt Instruction
with Idle Flag Set
RSM Instruction
with Idle Flag and
Halt Restart Slot Set
SMI#
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Halt Instruction
with Powerdown
Flag Set
RSM with
Powerdown Flag
and Halt Restart
Slot Set
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