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TI486 Microprocessor - Al Kossow's Bitsavers

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System Management Mode<br />

2.6 System Management Mode<br />

2.6.1 Introduction<br />

System Management Mode (SMM) provides an additional interrupt which can<br />

be used for system power management or software transparent emulation of<br />

I/O peripherals. SMM is entered using the Software Management Interrupt<br />

(SMI) which has a higher priority than any other interrupt, including NMI. After<br />

receiving an SMI, portions of the CPU state are automatically saved, SMM is<br />

entered and program execution begins at the base of SMM space<br />

(Figure 2-27 and Figure 2-28). Running in protected SMM address space,<br />

the interrupt routine does not interfere with the operating system or any<br />

application program.<br />

Seven SMM instructions have been added to the <strong>TI486</strong> instruction set that<br />

permit saving and restoring of the total CPU state when in SMM mode. Two<br />

new pins, SMI and SMADS, support SMM functions.<br />

Figure 2-27. <strong>TI486</strong>SLCIE Memory and 110 Address Spaces<br />

Physical<br />

Memory Space<br />

FFFFFFh~----~----~<br />

FF FFFFh<br />

Potential<br />

SMM Addres Space<br />

Physical<br />

Memory<br />

16 MBytes<br />

Defined<br />

SMM<br />

Address<br />

Space<br />

4 KBytes to<br />

16 MBytes<br />

SMADS<br />

active<br />

ADS<br />

active<br />

00 OOOOh --...~ ......... ___ ~_ ....<br />

Non-SMM Mode<br />

ADS Active<br />

00 OOOOh 1....-_____ ....<br />

SMM Mode<br />

2-51

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