VT82C596B datasheet(87/96 Pages) ETC

87 / 96 page

VT82C596B

Revision 0.3 June 17, 1999

-81-

Functional Descriptions

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Legacy Power Management Timers

In addition to the ACPI power management timer, the

VT82C596B includes the following four legacy power

management timers:

GP0 Timer: general purpose timer with primary event

GP1 Timer: general purpose timer with peripheral event

reload

Secondary Event Timer: to monitor secondary events

Conserve Mode Timer: Hardware-controlled return to

standby

The normal sequence of operations for a general purpose timer

(GP0 or GP1) is to

1) First program the time base and timer value of the initial

count (register GP_TIM_CNT).

2) Then activate counting by setting the GP0_START or

GP1_START bit to one:

the timer will start with the

initial count and count down towards 0.

3) When the timer counts down to zero, an SMI will be

generated if enabled (GP0TO_EN and GP1TO_EN in the

GBL_EN register) with status recorded (GP0TO_STS and

GP1TO_STS in the GBL_STS register).

4) Each timer can also be programmed to reload the initial

count and restart counting automatically after counting

down to 0.

This feature is not used in standard VIA

BIOS.

The GP0 and GP1 timers can be used just as the general

purpose timers described above. However, they can also be

programmed to reload the initial count by system primary

events or peripheral events thus used as primary event (global

standby) timer and peripheral timer, respectively.

The

secondary event timer is solely used to monitor secondary

events.

System Primary and Secondary Events

Primary system events are distinguished in the PRI_ACT_STS

and PRI_ACT_EN registers:

Bit Event

Trigger

7 Keyboard Access

I/O port 60h

6 Serial Port Access

I/O ports 3F8h-3FFh, 2F8h-2FFh,

3E8h-3EFh, or 2E8h-2EFh

5 Parallel Port Access I/O ports 378h-37Fh or 278h-27Fh

4 Video Access

I/O ports 3B0h-3DFh or memory

A/B segments

3 IDE/Floppy Access

I/O ports 1F0h-1F7h, 170h-177h,

or 3F5h

2 Reserved

1 Primary Interrupts

Each channel of the interrupt

controller can be programmed to

primary

secondary

interrupt

0 ISA Master/DMA Activity

Each category can be enabled as a primary event by setting the

corresponding bit of the PRI_ACT_EN register to 1.

enabled, the occurrence of the primary event reloads the GP0

timer if the PACT_GP0_EN bit is also set to 1. The cause of

the timer reload is recorded in the corresponding bit of

PRI_ACT_STS register while the timer is reloaded.

If no

enabled primary event occurs during the count down, the GP0

timer will time out (count down to 0) and the system can be

programmed (setting the GP0TO_EN bit in the GBL_EN

power down mode.

The VT82C596B distinguishes two kinds of interrupt requests

as far as power management is concerned: the primary and

secondary interrupts.

Like other primary events, the

occurrence of a primary interrupt demands that the system be

restored to full processing capability. Secondary interrupts,

however, are typically used for housekeeping tasks in the

background unnoticeable to the user. The VT82C596B allows

each channel of interrupt request to be declared as either

primary, secondary, or ignorable in the PIRQ_CH and

SIRQ_CH registers. Secondary interrupts are the only system

secondary events defined in the VT82C596B.

Like primary events, primary interrupts can be made to reload

the GP0 timer by setting the PIRQ_EN bit to 1. Secondary

interrupts do not reload the GP0 timer. Therefore the GP0

timer will time out and the SMI routine can put the system into

power down mode if no events other than secondary interrupts

are happening periodically in the background.

Primary events can be programmed to trigger an SMI (setting

of the PACT_EN bit). Typically, this SMI triggering is turned

off during normal system operation to avoid degrading system

performance.

Triggering is turned on by the SMI routine

before entering the power down mode so that the system may

be returned to normal operation at the occurrence of primary

events. At the same time, the GP0 timer is reloaded and the

count down process is restarted.

Peripheral Events

Primary and secondary events define system events in general

and the response is typically expressed in terms of system

events. Individual peripheral events can also be monitored by

the VT82C596B through the GP1 timer. The following four

categories of peripheral events are distinguished (via register

GP_RLD_EN):

Bit-7

Keyboard Access

Bit-6

Serial Port Access

Bit-4

Video Access

Bit-3

IDE/Floppy Access

The four categories are subsets of the primary events as

defined in PRI_ACT_EN and the occurrence of these events

can be checked through a common register PRI_ACT_STS.

As a peripheral timer, GP1 can be used to monitor one (or

more than one) of the above four device types by programming

the corresponding bit to one and the other bits to zero. Time

out of the GP1 timer indicates no activity of the corresponding

device type and appropriate action can be taken as a result.

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