Specifications

AMD Geode™ GeodeROM Functional Specification 211
15
System Management Mode Software 32087C
15.0System Management Mode Software
The System Management Mode (SMM) software for AMD Geode™ solutions has unique properties that allow for nontradi-
tional features. The SMM software, along with specialized hardware, allows the System Management Interrupt (SMI) han-
dler to simulate functionality normally associated with discrete devices (e.g., VGA, audio, UARTs, etc.). This is enhanced by
the Geode processor’s ability to enter SMM mode very quickly, and also the ability to service nested SMIs. In addition, the
SMM software controls power management, much like a traditional system.
There are several types of events that generate an SMI, thereby invoking the SMI handler.
Configurable I/O Traps:
The Geode device(s) support configuration of an I/O trap, range, and attributes; all of which can generate an SMI.
Special Traps:
The hardware contains specialized trapping ability, such as the occurrence of audio and video events, and the
reading and writing of UART or LPT I/O addresses.
General Purpose Timers:
The Geode device(s) contain several configurable timers. When a timer expires, the companion device generates an
SMI.
Inactivity Timers:
The hardware contains function-specific timers for power management. These are reset when user-activity occurs,
such as keyboard use. When the timer expires, an SMI is generated.
GPIO Activity:
The Geode device(s) contain some number of General Purpose I/O pins. The pins are configurable, to generate an
SMI if there is activity on a GPIO pin.
PCI Configuration Cycle:
The Geode device(s) can be configured to generate an SMI upon access to a select address in the PCI configuration
space.
The VSA2 software determines the cause of the SMI, generally by checking status registers. Then the System Manager
software dispatches control to the appropriate VSM.