54
2 System Board
The Input/Output Controller Hub (82801AA)
Interrupt Controller
The Interrupt controller is equivalent in function to the two 82C59 interrupt
controllers. The two interrupt controllers are cascaded so that 14 external
and two internal interrupts are possible. In addition, the ICH supports a
serial interrupt scheme and also implements the I/O APIC controller. A table
on
page 109
shows how the master and slave controllers are connected.
Timer/Counter Block
The timer/counter block contains three counters that are equivalent in
function to those found in one 82C54 programmable interval counter/timer.
These three counters are combined to provide the system timer function,
and speaker tone. The 14.318 MHz oscillator input provides the clock source
for these three counters.
Advanced Programmable
Interrupt Controller
Incorporated in the ICH, the APIC can be used in either single-processor or
multi-processor systems, while the standard interrupt controller is used in
single-processor systems.
Real-Time Clock
The RTC is 146818A-compatible, with 256 bytes of CMOS. The RTC
performs two key functions: keeping track of the time of day and storing
system data.
The RTC operates on a 32.768 kHz crystal and a separate 3V lithium battery
that provides up to 5 years of protection. It also supports two lockable
memory ranges. By setting bits in the configuration space, two 8-byte ranges
can be locked to read and write accesses. This prevents unauthorized
reading of passwords or other security information. Another feature is a
date alarm allowing for a schedule wake-up event up to 30 days in advance.
Enhanced Power
Management
The ICH’s power management functions include enhanced clock control,
local and global monitoring support for 14 individual devices, and various
low-power (suspend) states. A hardware-based thermal management circuit
permits software-independent entry points for low-power states.
The ICH includes full support for the Advanced Configuration and Power
Interface (ACPI) specifications.
