Chapter 5. Interrupt assignment and interrupt sharing
Interrupt assignment and interrupt sharing are two areas in
which many system-adapter incompatibilities occur. Interrupt
assignment is done by the PCI initialization BIOS code, or
manually (on systems not providing automatic PCI configuration).
There are a few critical factors regarding PCI interrupts:
A) The Auto LANStreamer must have a PCI 'level sensitive'
interrupt line assigned. This allows multiple devices to
share the interrupt. It is not the same as ISA 'edge
triggered' interrupts, which cannot be shared.
B) The interrupt assigned must not be shared with any ISA
device. (Additionally, it is recommended that PCI interrupts
not be shared with EISA, or Micro Channel adapters.)
C) We recommend that each LANStreamer PCI adapter be assigned its
own interrupt (if possible). Sharing interrupts among PCI
devices is allowed by the PCI spec, but some early PCI systems
have bugs that can be avoided by not sharing interrupts.
D) Interrupt 0 is reserved for the system timer, and cannot be
used for the Auto LANStreamer PCI adapter.
When multiple PCI adapters share an interrupt, a problem with
one adapter can appear as a performance, or functional problem
with a different adapter. When debugging system problems try to
isolate each adapter on its own interrupt (if possible).
IBM's 80486 VL/PCI systems (Models 6573, 6583, 6484, 6494, etc.)
with multiple PCI adapters installed should assign one interrupt
per adapter. This same recommendation applies to other systems
based on the Opti 802 VL-bus to PCI-bus chip.
In the system setup, leave all three interrupts available for
the PCI bus (not assigned to ISA devices) if possible. The
system will automatically configure one adapter per interrupt
if sufficient interrupts are available when the adapters are
If this is not done, and multiple adapters share a single
interrupt, spurious interrupts may occur.
Under Novell Netware, the message Spurious Interrupt Received
may appear. This has been observed on some systems even though
the system operates correctly. This occurred when multiple
PCI devices shared an interrupt, and the system interrupt
controller occasionally generated duplicate interrupts to the
If your system is running properly, and you wish to suppress
this message, the command is:
Set Display Spurious Interrupt Alert = OFF
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