NH82801HBM S LB9A Intel, NH82801HBM S LB9A Datasheet - Page 205

• Manufacturer Part Number: NH82801HBM S LB9A
• Description: CONTROLLER HUB, ICH8M, I/O, 82801HBM
• Manufacturer: Intel

Specifications of NH82801HBM S LB9A

• Power Dissipation Pd: 2.4W
• Digital Ic Case Style: BGA
• No. Of Pins: 676
• Pci Bus Type: I/O Controller Hub
• Pci Express Base Spec: PCIe 1.1
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Functional Description
5.17.5
5.17.6
5.17.7
Intel
®
ICH8 Family Datasheet
Interrupt Levels
Interrupts directed to the internal 8259s are active high. See
information regarding the polarity programming of the I/O APIC for detecting internal
interrupts.
If the interrupts are mapped to the I/O APIC and set for level-triggered mode, they can
be shared with PCI interrupts. This may be shared although it’s unlikely for the
operating system to attempt to do this.
If more than one timer is configured to share the same IRQ (using the
TIMERn_INT_ROUT_CNF fields), then the software must configure the timers to level-
triggered mode. Edge-triggered interrupts cannot be shared.
Handling Interrupts
If each timer has a unique interrupt and the timer has been configured for edge-
triggered mode, then there are no specific steps required. No read is required to
process the interrupt.
If a timer has been configured to level-triggered mode, then its interrupt must be
cleared by the software. This is done by reading the interrupt status register and
writing a 1 back to the bit position for the interrupt to be cleared.
Independent of the mode, software can read the value in the main counter to see how
time has passed between when the interrupt was generated and when it was first
serviced.
If Timer 0 is set up to generate a periodic interrupt, the software can check to see how
much time remains until the next interrupt by checking the timer value register.
Issues Related to 64-Bit Timers with 32-Bit Processors
A 32-bit timer can be read directly using processors that are capable of 32-bit or 64-bit
instructions. However, a 32-bit processor may not be able to directly read 64-bit timer.
A race condition comes up if a 32-bit processor reads the 64-bit register using two
separate 32-bit reads. The danger is that just after reading one half, the other half rolls
over and changes the first half.
If a 32-bit processor needs to access a 64-bit timer, it must first halt the timer before
reading both the upper and lower 32-bits of the timer. If a 32-bit processor does not
want to halt the timer, it can use the 64-bit timer as a 32-bit timer by setting the
TIMERn_32MODE_CNF bit. This causes the timer to behave as a 32-bit timer. The upper
32-bits are always 0.
Section 5.9
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