Grand Interconnect Architecture

The Grand Interconnect architecture is illustrated in Figure . It includes a single host computer interface which initiates all transactions except for Asynchronous Event Notification transactions which can be generated by any slave node and inserted in the data stream between messages. The host interface can initiate one of four general messages:

Read Request

This message is generated by the host to read one or more items from the addressed slave I/O chassis.

Write Request

This message is generated by the host to write one or more items to the addressed slave I/O chassis.

Control

This message is generated by the host to effect a control operation at the addressed slave I/O chassis

Trigger

This message is generated by the host to generate an asynchronous event (trigger) at the addressed I/O chassis. If the message is addressed to chassis "0'', the trigger is accepted by all I/O chassis.

Each message type includes a 7-bit "chassis address'' which identifies the chassis to which the message is being sent. Data transfer messages include additional fields including VXI address modifier, 32-bit VXI address, and for block operations a 32-bit transfer count. Write requests include the write data. Read requests cause the addressed chassis to generate a Read Reply with the data that was read. Trigger requests include a data word that identify which trigger is to be generated at the addressed I/O chassis.

Other message types include:

Asynchronous Event

This message is generated by a slave node to inform the host of an asynchronous event, e.g. selected interrupt or trigger line event.

Read Reply

This message is generated by a slave node in response to a read request and identifies the start of data. Following the data is read status.

Write Reply

This message is generated by a slave node in response to a write request. Its primary function is to pass write status back to the host.

Control Reply

This message is generated by a slave node in response to a control request and includes control status information.

Trigger Reply

This message is generated by a slave node in response to a trigger message (except in response to a broadcast trigger) and includes status.

Suspend Transfer

This message is generated by a host node when a slave is sending data faster than it can process it, or by a slave node when the host is sending data faster than it can process it.

Continue Transfer

This message is generated by the node which issued the suspend to resume data transmission.

In addition, each node includes FIFO buffering of the input serial stream. The FIFO provides sufficient buffering of the incoming data stream to permit the throttling mechanism (Suspend Transfer) time to suspend the incoming stream and allow the receiving node time to catch up before a Continue Transfer is issued. The throttling mechanism uses the FIFO half-full flag transitions to control throttling. This method insures that the device that is limiting the transfer rate always has a queue of work to perform.

Error Detection
Synchronization Features