SB82371 Intel Corporation, SB82371 Datasheet - Page 107

• Manufacturer Part Number: SB82371
• Description: 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR
• Manufacturer: Intel Corporation

The system BIOS should incorporate one of the following recommendations:
3.11.
The PIIX/PIIX3 provides positive decode (chip selects) and X-Bus buffer control (XDIR# and XOE#) for a real
time clock, keyboard controller and BIOS for PCI and ISA initiated cycles. The PIIX/PIIX3 also generates
RTCALE (address latch enable) for the RTC. The chip selects are generated combinatorially from the ISA
SA(16:0) and LA (23:17) address lines (Note that it is assumed that ISA masters drive SA(19:16) and
LA(23:17) low when accessing I/O devices). The PIIX/PIIX3 also provides PS/2 mouse support via the
IRQ12/M signal and coprocessor functions (FERR# and IGNNE#). The chip selects and X-Bus buffer control
lines can be enabled/disabled via the XBCS Register.
Coprocessor Error Function
This function provides coprocessor error support for the CPU and is enabled via the XBCS Register. FERR#
is tied directly to the coprocessor error signal of the CPU. If FERR# is driven active to the PIIX, an internal
IRQ13 is generated and an the INTR output from the PIIX/PIIX3 is driven active. When a write to I/O location
F0h is detected, the PIIX/PIIX3 negates IRQ13 (internal to the PIIX) and drives IGNNE# active. IGNNE#
remains active until FERR# is driven inactive. Note, that IGNNE# is not driven active unless FERR# is active.
Mouse Function
When the mouse interrupt function is enabled (via the XBCS Register), the mouse interrupt function is
provided on the IRQ12/M input signal. In this mode, a mouse interrupt generates an interrupt through IRQ12
to the Host CPU. The PIIX/PIIX3 informs the CPU of this interrupt via a INTR. A read of 60h releases IRQ12.
If the mouse interrupt function is disabled, a read of address 60h has no effect on IRQ12/M. Reads and
writes to this register flow through to the ISA Bus. For additional information, see the IRQ12/M description in
the Signal Description.
X-Bus Peripheral Support
Pentium® uni-processor or dual processor with IO-APIC: Affects systems which use Local APIC in
Virtual Wire mode of operation. This can include Intel 430HX PCIset based systems with PIIX3 and
an IO-APIC. See recommendations below.
Pentium® Pro (uni-processor or dual processor): No impact as the Pentium® Pro processor INTR
signal does not require an INTR deassertion. This includes Intel 440FX PCIset based systems with
PIIX3.
1.
2.
3.
In Dual processor systems with only a single processor installed, the Local APIC should be
disabled (placed in Bypass or Masked Mode). If a second processor is later installed, the
multiprocessing operating system may need to be reinstalled.
To overcome the minimum deassertion requirement in dual processor systems with both
processors installed, set the Pentium® processor register TR12 bit 14 to ‘1’. This solution
should be used in systems whose software uses interrupt gate or task gate interrupt handling.
This solution should not be used if the system has software with uses trap gate interrupt
handling latency times.
In dual processor systems with both processors installed, the IO-APIC can be placed into
Virtual Wire model of operation via the IO-APIC. This solution can result in increased system
interrupt handling latency times.
82371FB (PIIX) AND 82371SB (PIIX3)
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