82371AB Datasheet, PDF (269/284 Pages) Intel Corporation – PCI-TO-ISA / IDE XCELERATOR PIIX4

E
82371AB (PIIX4)
Power Management Timer Programming Information:
Clock Frequency: 3.579545 MHz (14.31818 MHz/4 clock)
Start Count: 24 bit
[TMR_VAL]
Timer Overflow Status:
[TMROF_STS]
SCI Generation
[TMROF_EN]
11.6.3. GLOBAL LOCK
If the BIOS and ACPI software share resources via a common I/O port, the Global Lock feature must be used as
a semaphore to arbitrate access to these shared resources. For example, if both the BIOS and the ACPI driver
use the system management microcontroller control/status ports to manage the system, this access must be
controlled using the Global Lock feature.
In the event of a resource conflict, the Global Lock logic is used by the ACPI driver to inform the BIOS driver that
it is finished using a shared resource. The BIOS software accesses the GBL_RLS bit to attempt to gain
ownership of the lock. This access sets the BIOS_STS bit. ACPI software releases the lock by setting the
BIOS_EN bit. PIIX4 then generates an SMI which informs BIOS software that the shared resource is now
available.
Likewise, if the ACPI attempts to use the shared resources and there is a conflict, the Global Lock logic is used
by the BIOS software to inform the ACPI driver that it is finished using the shared resource. The ACPI software
accesses the BIOS_RLS bit to attempt to gain ownership of the lock. This access sets the GBL_STS bit. BIOS
software releases the lock by setting the GBL_EN bit. PIIX4 then generates an SCI which informs ACPI software
that the shared resource is now available.
PRELIMINARY
269
4/9/97 2:23 PM PIIX4aDS
INTEL CONFIDENTIAL
(until publication date)