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OpenVMS does not support sharing of interrupt lines or IRQ in the shared
ISA/PCI slot. Any use of OpenVMS with this type of shared slot could cause
unpredicatable results. This was the case with the shared ISA/PCI slot
closest to the motherboard on the AlphaStation 255.
One some systems the shared ISA/PCI slot shares only the back-pannel cutout
for connectors, but is electrically seperate and does not share IRQs. The
only limitation in this configuration is the total number of ISA and PCI
cards. OpenVMS *does* support this configuration.
Sorry, but I don't remember which type of shared shot is implemented on the
AlphaServer 400. I'm only aware of the AS 255, which has the unsupported
version of the ISA/PCI slot, but there may be others.
OpenVMS support for shared interrupts is under consideration for a future
release.
-Paul
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| The AlphaServer 400 (like the AlphaStation it's based on) provides four
interrupt lines for the embedded SCSI controller and the three PCI
slots. If the device in each PCI slot uses only one interrupt (INTA#),
then there is no need to "share" the interrupt lines at this level.
[Note that the AlphaStation 255 has additional embedded PCI devices,
and ran over the four-interrupt limit; so that system has to share.]
These four PCI interrupt lines are routed through the standard ISA
interrupt controller, and can be allocated to ISA IRQ lines 3-7, 9-12,
14 and 15 (I don't remember how each operating system does this). There
can be some contention if you have ISA devices that use a lot of
interrupts, or that demand a specific interrupt that another device
also requires.
The simple answer is: yes, the PCI/ISA combo slot is supported under
OpenVMS on the AlphaServer 400.
-- Kenny House
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