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TI486 Microprocessor - Al Kossow's Bitsavers

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System Management Mode<br />

Figure 2-28. <strong>TI486</strong>DLCIE Memory and I/O Address Spaces<br />

Physical<br />

Memory Space<br />

FFFFFFFFh~----------~<br />

FFFF FFFFh<br />

Potential<br />

SMM Address Space<br />

Physical<br />

Memory<br />

4 GBytes<br />

Defined<br />

SMM<br />

Address<br />

Space<br />

4 KBytes to<br />

16 MBytes<br />

SMADS<br />

active<br />

ADS<br />

active<br />

0000 OOOOh ...... __ ~ ______ ---'<br />

Non-SMM Mode<br />

ADS Active<br />

0000 OOOOh ...... __________ ---'<br />

SMM Mode<br />

2.6.2 SMM Operations<br />

8MM operation is summarized in Figure 2-29. Entering 8MM requires the<br />

assertion of the 8MI pin for at least four CLK2 periods. For the SMI input to be<br />

recognized, the following configuration register bits must be set as shown<br />

below:<br />

SMI<br />

8MAC<br />

SM4<br />

ARR4<br />

CCR1(1) =1<br />

CCR1(2) = 0<br />

CCR1 (7) = 1<br />

8IZE(3-0) > 0<br />

The configuration registers are discussed in detail earlier in this chapter. After<br />

recognizing 8MI and prior to executing the 8MI service routine, some of the<br />

CPU state information is changed. Prior to modification, this information is<br />

automatically saved in the 8MM memory space header located at the top of<br />

the 8MM memory space. After the header is saved, the CPU enters real mode<br />

and begins executing the 8MI service routine starting at the SMM memory<br />

base address.<br />

The SMI service routine is user definable and may contain system or power<br />

management software. If the power management software forces the CPU to<br />

power down, or if the SMI service routine modifies more than what is<br />

automatically saved, the complete CPU state information must be saved.<br />

2-52<br />

Programming Interface

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