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4. Addressing > I/O Space
32
PEB383 User Manual
July 25, 2011
Integrated Device Technology, Inc.
Confidential - NDA Required
Figure 10: 64-bit Prefetchable Memory Address Range
4.4
I/O Space
I/O Base, I/O Limit, I/O Base Upper 16 Bits, and I/O Limit Upper 16 Bits registers in the PEB383
configuration header specify an address range that is used by the bridge to determine whether to
forward I/O read and I/O write transactions across the bridge. If the address specified by the I/O Base
and I/O Base Upper 16 Bits registers is set to a value greater than the address specified by the I/O Limit
and I/O Limit Upper 16 Bits registers, the address range is disabled.
The response of the bridge to I/O transactions is controlled by the following configuration register bits:
•
I/O Space Enable bit in
“PCI Control and Status Register”
•
Bus Master Enable bit in
“PCI Control and Status Register”
•
ISA Enable bit in
“PCI Bridge Control and Interrupt Register”
•
VGA Enable bit in
“PCI Bridge Control and Interrupt Register”
The I/O Enable
bit must be set for any I/O transaction to be forwarded downstream. If this bit is not set,
all I/O transactions on the PCI bus are forwarded to the PCIe link. If this bit is not set, all PCIe
Interface I/O requests are completed with Unsupported Request status.
Primary Interface
Downstream
Upstream
Memory Mapped I/O
4 GB Boundary
4 GB Boundary
Secondary Interface
Prefetchable Memory
Primary Interface
Downstream
Upstream
Memory Mapped I/O
4 GB Boundary
4 GB Boundary
Secondary Interface
Prefetchable Memory