TABLE OF CONTENTS Conventional PCI has no means for one device/function to communicate explicitly with another device/function other than in Configuration Space, which serves a very specific and limited function. The Device ID Message (DIM) command provides a mechanism for an initiator to send an arbitrary message directly to a target device/ function outside of the address spaces Memory, I/O, Configuration defined for the bus. The target of a DIM command is called the Completer.
Device ID Messages are burst-push transactions. The initiator is the source of the data. The message may be any length up to 4096 bytes.
Support of the DIM command is optional for non-bridge PCI-X devices. If a device that does not support the DIM command is the target of a Device ID Message, it doesn't respond and the transaction terminates with Master Abort.
Figure 12-10 shows the layout of the Address phase of a DIM command. Message Class identifies one of 16 message types. Currently the value zero is called "Vendor Defined," and all other values are reserved by the PCI SIG [2]. The field Class Specific is available to further classify a message. If the message has a 64-bit address, then the upper 32 bits are also part of the Class Specific field. The Completer address fields identify the target of this message. The remaining 2 bits will be dealt with below.
Figure 12-11 shows the layout of the Attribute phase of a DIM command. It is...
