2 system management mode support – Intel 386 User Manual
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Intel386™ EX EMBEDDED MICROPROCESSOR USER’S MANUAL
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14.3.2 System Management Mode Support
The processor supports four operating modes: system management mode (SMM), protected, real
and virtual-86 mode. In order for a system to operate correctly in SMM, it must meet several re-
quirements. The CSU provides support for some of these requirements. To use SMM, you must
set aside a partition of memory, called SMRAM, for the SMM driver. SMRAM must meet the
following conditions:
•
Located at 38000H–3FFFFH (32 Kbytes)
•
Accessible only when the processor is in SMM during normal operation
•
Accessible during system initialization when the processor is not in SMM
The CSU allows you to specify an address block and control whether or not the chip-select is ac-
tivated while the processor is in SMM. While in SMM (with CASMM=1), the chip-select is ac-
tive only when the processor is the bus master, such as when the processor is not in a hold state.
Refer to Chapter 7 (“Programming Considerations” on page 7-16) for a code example of pro-
gramming chip-selects to support SMM.