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I2O Interface
I2O Compatible Address Translation Unit
104
Corp.
EPC User
’
s Manual Revision 1.05
Copyright 1997-2000, V3 Semiconductor
Figure 53: Operation of the I2O Address Translation Function and In/Outbound Free/
Post List Mapping
12.2.1
ATU Setup and Configuration
The I
2
O compatible ATU is configured through 2 registers:
PCI_I2O_BASE determines where in PCI system address space the ATU will be
located
PCI_I2O_MAP determines the size of the ATU aperture and the location of the
aperture within local address space.
12.2.1.1
PCI_I2O_BASE Operation
The PCI_I2O_BASE register provides a standard PCI - I
2
O compatible Address Translation
Unit. It provides two main functions:
Access to the I
2
O inbound/outbound free list and post list FIFOs.
An aperture into Local Bus address space that translates a PCI address into a local
bus address.
The bottom 4K bytes of the aperture are not translated into local bus address space. In this
4K region only 16 bytes are used (0x30-0x37, 0x40-0x47) for the inbound/outbound
registers. The I2O specification requires no other ports in this 4K space and the remainder
of that space is reserved.
PCI Address Space
Local Address Space
Paper tape
reserved
Aperture into Local
Address Space
Inbound FIFO Port
Outbound FIFO Port
PCI_I2O_BASE
PCI_I2O_BASE+0x40
PCI_I2O_BASE+0x44
PCI_I2O_BASE+0x1000
Address
Translation
(PCI_I2O_MAP)
Local Address
Space Accessible
from Host Space
4K Bytes Not
Mapped into Host
PCI_I2O_MAP+0x1000
PCI_I2O_MAP
Inbound Post List
Inbound Free List
Outbound Post List
Outbound Free List
Inbound Free Tail
Inbound Post Head
reserved
QBA_MAP
Outbound Post Tail
Outbound Free Head
High Memory Address
Low Memory Address
Outbound Int. Mask
Outbound Int. Status
PCI_I2O_BASE+0x30
PCI_I2O_BASE+0x34