User`s guide

3.3.2.14 Guaranteed Access-Time Mode
The Intel 82378ZB ISA bridge provides three sideband signals (flushreq_l,
memreq_l, and memack_l) to provide mechanisms for flushing system write
buffers and to allow a guaranteed access time of 2.1 s to a master on the
ISA bus. The flushreq_l and memreq_l signals are outputs from the bridge;
memack_l is an input to the bridge.
Note
Guaranteed access-time mode is not supported on the AlphaPC64.
3.3.2.15 Interrupts
The 21071-DA interrupts the CPU by using the int_hw0 signal when it has
errors to report. The 21071-DA does not distinguish between hard and soft
errors when asserting the interrupt signal.
The 21071-DA does not provide an interval timer interrupt. This functionality
should be provided to the CPU by some other device in the system. In addition,
interrupts from other PCI devices or from a PCI interrupt controller must be
sent directly to the CPU without intervention.
The 21071-DA participates in the interrupt acknowledge process. It responds
to CPU read block commands directly to the interrupt acknowledge address
space, which triggers the 21071-DA to perform an interrupt acknowledge
transaction on the PCI. The interrupt vector returned on the PCI is returned
to the CPU through the sysBus by the 21071-DA.
Functional Description 3–19