TABLE OF CONTENTS The agents participating in a conventional PCI transaction are designated as the initiator and the target. The initiator is the agent that initiates the transaction, the target is the agent selected by the initiator to respond, i.e., the target of the transaction. PCI-X introduces two new terms necessary to identify the agents participating in a Split Transaction. The requester is the agent that first introduces a transaction onto the PCI-X bus. When requesting the transaction, it is the initiator.
The completer is the agent that ultimately completes the transaction. During the initial request phase, the completer is the target. Later, when it is ready to complete the transaction, the completer becomes the initiator and the original requester becomes the target.
A target that is unable to complete a transaction in a timely manner responds to the requestor with a split response, as illustrated in Figure 12-5. The target claims the transaction normally by asserting DEVSEL#. But, in what would normally be the first data phase with IRDY# and TRDY# asserted, the target negates DEVSEL#. Thus, no data transfer occurs, and the requester is notified that the target will complete the transaction later.
The target may terminate any transaction except memory write with a Split Response. That is, memory reads, interrupt acknowledge, all I/O and all configuration transactions may be terminated with Split Response. For a read transaction, the target must drive the AD
