На него вообще не нужно отвечать, транзакции этого типа адресованы непосредственно системному контроллеру прерываний.
Цитата
Interrupt requests (that use INTx#) do not appear as transactions on the PCI bus (they are sideband signals) and, therefore, have no ordering relationship to any bus transactions. Furthermore, the system is not required to use the Interrupt Acknowledge bus transaction to service interrupts. So interrupts are not synchronizing events and device drivers cannot depend on them to flush posting buffers. However, when MSI are used, they have the same ordering rules as a memory write transaction (refer to Section 6.8 for more information).
Цитата
An Interrupt Acknowledge transaction has no addressing mechanism and is implicitly targeted to the interrupt controller in the system.)
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