Geode GXLV Processor Series Low Power Integrated x86 Solutions

Processor Programming (Continued)3.7 SYSTEM MANAGEMENT MODESystem Management Mode (SMM) is an enhancement ofthe standard x86 architecture. SMM is usually employedfor system power management or software-transparentemulation of I/O peripherals. SMM is entered through ahardware signal “System Management Interrupt” (SMI#pin) that has a higher priority than any other interrupt,including NMI. An SMM interrupt can also be triggeredfrom software using an SMINT instruction. Following anSMM interrupt, portions of the CPU state are automaticallysaved, SMM is entered, and program executionbegins at the base of SMM address space (Figure 3-9).FFFFFFFFhPhysicalMemory SpaceThe GXLV processor extends System Management Modeto support the virtualization of many devices, includingVGA video. The SMM mechanism can be triggered notonly by I/O activity, but by access to selected memoryregions. For example, SMM interrupts are generatedwhen VGA addresses are accessed. As will be described,other SMM enhancements have reduced SMM overheadand improved virtualization-software performanceFFFFFFFFhPotentialSMM AddressSpaceGeode GXLV Processor SeriesPhysical Memory4GB4KBto32MBDefinedSMMAddressSpace00000000hNon-SMM00000000hSMMFigure 3-9. System Management Memory Address SpaceRevision 1.3 83 www.national.com