Product specifications

VT8235 V-Link South Bridge
Revision 1.22 October 24, 2002 -135- Functional Descriptions
Legacy Power Management Timers
In addition to the ACPI power management timer, the VT8235
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 Timer Count).
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 (GP0 Timeout Enable and GP1
Timeout Enable in the Global Enable register) with status
recorded (GP0 Tomeout Status and GP1 Timeout Status
in the Global Status 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 Primary
Activity Status and Primary Activity Enable 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
be a primary or secondary
interrupt
0 ISA Master/DMA Activity
Each category can be enabled as a primary event by setting the
corresponding bit of the Primary Activity Enable register to 1.
If enabled, the occurrence of the primary event reloads the
GP0 timer if the Primary Activity GP0 Enable bit is also set to
1. The cause of the timer reload is recorded in the
corresponding bit of Primary Activity Status 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 GP0 Timeout
Enable bit in the Global Enable register to one) to trigger an
SMI to switch the system to a power down mode.
The VT8235 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 VT8235 allows
each channel of interrupt request to be declared as either
primary, secondary, or ignorable in the Primary IRQ Channel
and Secondary IRQ Channel registers. Secondary interrupts
are the only system secondary events defined in the VT8235.
Like primary events, primary interrupts can be made to reload
the GP0 timer by setting the PIRQ Enable 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 Primary Activity Enable 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 VT8235 through the GP1 timer. The following four
categories of peripheral events are distinguished (via the GP
Reload Enable register):
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 Primary Activity Enable and the occurrence of
these events can be checked through a common register
Primary Activity Status. 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.