Intel® 82854 Graphics Memory Controller Hub (GMCH)

2.9System Interrupts

The GMCH supports both the legacy Intel 8259 Programmable Interrupt delivery mechanism and the Intel Celeron M processor FSB interrupt delivery mechanism. The serial APIC Interrupt mechanism is not supported.

The Intel 8259 Interrupt delivery mechanism support consists of flushing in bound Hub interface write buffers when an Interrupt Acknowledge cycle is forwarded from the system bus to the Hub interface.

PCI MSI interrupts are generated as memory writes. The GMCH decodes upstream memory writes to the range 0FEE0_0000h - 0FEEF_FFFFh from the Hub interface as message based interrupts. The GMCH forwards the memory writes along with the associated write data to the system bus as an Interrupt Message transaction. Since this address does not decode as part of main system memory, the write cycle and the write data do not get forwarded to system memory via the write buffer. The GMCH provides the response and HTRDY# for all Interrupt Message cycles including the ones originating from the GMCH. The GMCH also supports interrupt redirection for upstream interrupt memory writes.

For message based interrupts, system write buffer coherency is maintained by relying on strict ordering of memory writes. The GMCH ensures that all memory writes received from a given interface prior to an interrupt message memory write are delivered to the system bus for snooping in the same order that they occur on the given interface.

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D15343-003

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Intel D15343-003 manual System Interrupts