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I2O Interface
Inbound/Outbound Queue Management
Copyright 1997-2000, V3 Semiconductor Inc.
EPC User
’
s Manual Revision 1.05
105
12.2.2
PCI_I2O_MAP Operation
Local bus memory can be accessed by a PCI master through the PCI_I2O_BASE register.
The base address on the local bus is translated into a local bus address according to the
value in the PCI_I2O_MAP register. This forms the local bus side of the I
2
O compatible
“
Address Translation Unit
”
. The PCI address is translated into a local bus address in the
following manner:
Local Bus Address =
PCI Address - PCI_I2O_BASE Base Address + PCI_I2O_MAP
Address
Where:
PCI Address is within the aperture size defined by the PCI_I2O_MAP register
PCI_I2O_BASE Base Address is on an aperture sized boundary
PCI_I2O_MAP Address is on an aperture sized boundary
12.3
INBOUND/OUTBOUND QUEUE MANAGEMENT
An I2O driver operating on the host or external PCI agent will exchange Message Frame
Addresses (MFA) with the local processor (acting as the Intelligent I/O processor). The
exchange of these MFAs is managed as a circular queue or FIFO (first in first out) storage.
The physical storage of the MFAs is in external memory on the local bus (the I2O
specification itself doesn
’
t make any assumptions about where the storage is located).
There are 2 pairs of queues provided:
The inbound free list and post list queues
The outbound free list and post list queues
For each of the 4 queues in memory data flows in only a single direction: either PCI-to-Local
orLocal-to-PCI. The following diagram illustrates the flow of data in and out of these queues
located in local memory.