Compaq 850 manual SMI- Generation, Iochk- Nmi

Chapter 4 System Support

The NMI Status Register at I/O port 061h contains NMI source and status data as follows:

NMI Status Register 61h

Bit	Function
7	NMI Status:
	0	= No NMI from system board parity error.
	1	= NMI requested, read only
6	IOCHK- NMI:
	0	= No NMI from IOCHK-
	1	= IOCHK- is active (low), NMI requested, read only

5Interval Timer 1, Counter 2 (Speaker) Status

4Refresh Indicator (toggles with every refresh)

3IOCHK- NMI Enable/Disable:

0 = NMI from IOCHK- enabled

1 = NMI from IOCHK- disabled and cleared (R/W)

2System Board Parity Error (PERR/SERR) NMI Enable: 0 = Parity error NMI enabled

1 = Parity error NMI disabled and cleared (R/W)

1 Speaker Data (R/W)

0Inteval Timer 1, Counter 2 Gate Signal (R/W) 0 = Counter 2 disabled

1 = Counter 2 enabled

Functions not related to NMI activity.

After the active NMI has been processed, status bits <7> or <6> are cleared by pulsing bits <2> or <3> respectively.

The NMI Enable Register (070h, <7>) is used to enable/disable the NMI signal. Writing 80h to this register masks generation of the NMI-. Note that the lower six bits of register at I/O port 70h affect RTC operation and should be considered when changing NMI- generation status.

SMI- Generation

The SMI- (System Management Interrupt) is typically used for power management functions. When power management is enabled, inactivity timers are monitored. When a timer times out, SMI- is asserted and invokes the microprocessor’s SMI handler. The SMI- handler works with the APM BIOS to service the SMI- according to the cause of the timeout.

Although the SMI- is primarily used for power managment the interrupt is also employed for the QuickLock/QuickBlank functions as well.

4-18Compaq Deskpro EXS and Workstation 300 Personal Computers Featuring the Intel Pentium 4 Processor

First Edition - December 2000