307013-003 Datasheet, PDF (147/848 Pages) Intel Corporation – Intel I/O Controller Hub 7

Functional Description
5.12.2
5.12.3
5.12.4
5.12.5
Interrupts
The real-time clock interrupt is internally routed within the ICH7 both to the I/O APIC
and the 8259. It is mapped to interrupt vector 8. This interrupt does not leave the
ICH7, nor is it shared with any other interrupt. IRQ8# from the SERIRQ stream is
ignored. However, the High Performance Event Timers can also be mapped to IRQ8#;
in this case, the RTC interrupt is blocked.
Lockable RAM Ranges
The RTC’s battery-backed RAM supports two 8-byte ranges that can be locked via the
configuration space. If the locking bits are set, the corresponding range in the RAM will
not be readable or writable. A write cycle to those locations will have no effect. A read
cycle to those locations will not return the location’s actual value (resultant value is
undefined).
Once a range is locked, the range can be unlocked only by a hard reset, which will
invoke the BIOS and allow it to relock the RAM range.
Century Rollover
The ICH7 detects a rollover when the Year byte (RTC I/O space, index offset 09h)
transitions form 99 to 00. Upon detecting the rollover, the ICH7 sets the
NEWCENTURY_STS bit (TCOBASE + 04h, bit 7). If the system is in an S0 state, this
causes an SMI#. The SMI# handler can update registers in the RTC RAM that are
associated with century value. If the system is in a sleep state (S1–S5) when the
century rollover occurs, the ICH7 also sets the NEWCENTURY_STS bit, but no SMI# is
generated. When the system resumes from the sleep state, BIOS should check the
NEWCENTURY_STS bit and update the century value in the RTC RAM.
Clearing Battery-Backed RTC RAM
Clearing CMOS RAM in an ICH7-based platform can be done by using a jumper on
RTCRST# or GPI. Implementations should not attempt to clear CMOS by using a
jumper to pull VccRTC low.
Using RTCRST# to Clear CMOS
A jumper on RTCRST# can be used to clear CMOS values, as well as reset to default,
the state of those configuration bits that reside in the RTC power well. When the
RTCRST# is strapped to ground, the RTC_PWR_STS bit (D31:F0:A4h bit 2) will be set
and those configuration bits in the RTC power well will be set to their default state.
BIOS can monitor the state of this bit, and manually clear the RTC CMOS array once the
system is booted. The normal position would cause RTCRST# to be pulled up through a
weak pull-up resistor. Table 5-21 shows which bits are set to their default state when
RTCRST# is asserted. This RTCRST# jumper technique allows the jumper to be moved
and then replaced—all while the system is powered off. Then, once booted, the
RTC_PWR_STS can be detected in the set state.
Intel ^® ICH7 Family Datasheet
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