2. PCI Interface
62
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
2.6
I
2
O Shell Interface
PowerSpan II provides portions of the I
2
O Shell Interface for the platform it is connecting to the
Primary PCI bus. The I
2
O Shell Interface defined in the
I
2
O 2.0 Specification
is comprised of three
main sections:
•
messaging interface
•
protocol for exchanging messages
•
executive class messages
PowerSpan II implements the I
2
O messaging interface and, in conjunction with the Input/Output
Processor (IOP), enables the message passing protocol.
2.6.1
I
2
O Target Image
There are three registers which enable Memory access to the I
2
O Shell Interface and local IOP
Message Frames. The supporting registers include the following:
•
“PCI-1 I2O Target Image Base Address Register” on page 257
•
“PCI I2O Target Image Control Register” on page 352
•
“PCI I2O Target Image Translation Address Register” on page 356
The I
2
O Shell Interface consists of Inbound and Outbound Queues and supporting I
2
O Host interrupt
registers. The queues contain Message Frame Addresses (MFAs). These MFAs specify the starting
address of Message Frames relative to the base address of the memory window in PowerPC memory.
PowerSpan II implements I
2
O support with the first Memory Base Address Register in PCI
configuration space.
The I
2
O target image is divided into an I
2
O Shell Interface and a processor bus memory window
intended for IOP Message Frame accesses. The I
2
O Shell Interface is accessed through the lower 4
Kbytes of the I
2
O target image. I
2
O Shell Interface accesses are limited to 32-bit single data phase PCI
transactions. Accesses through the I
2
O target image memory window to IOP Message Frames are
burstable up to 64-bits wide for PCI-1, but limited to 32-bit wide for PCI-2.
PowerSpan II does not support posting of more than one write transaction to the Inbound or Outbound
Queue. Attempts to write to the Inbound or Outbound Queue are retried until the currently active write
completes on the Processor Bus Interface.
The I
2
O target image does not support Master-Based Decode.