Intel 80312 I/O Companion Chip - ECEE

Intel ® 80312 I/O Companion ChipMessaging Unit6.5 Circular QueuesThe MU implements four circular queues. There are two inbound queues and two outboundqueues. In this case, inbound and outbound refer to the direction of the flow of posted messages.Inbound messages are either:• posted messages by other processors for the Intel ® 80200 processor to process or• free (or empty) messages that can be reused by other processors.Outbound messages are either:• posted messages by the Intel ® 80200 processor for other processors to process or• free (or empty) messages that can be reused by the Intel ® 80200 processor.Therefore, free inbound messages flow away from the Intel ® 80200 processor and free outboundmessages flow toward the Intel ® 80200 processor.The four Circular Queues are used to pass messages in the following manner. The two inboundqueues are used to handle inbound messages and the two outbound queues are used to handleoutbound messages. One of the inbound queues is designated the Free queue and it contains inboundfree messages. The other inbound queue is designated the Post queue and it contains inbound postedmessages. Similarly, one of the outbound queues is designated the Free queue and the other outboundqueue is designated the Post queue. Table 6-3 contains a summary of the queues.Table 6-3.Circular Queue SummaryQueue Name Purpose Action on PCI InterfaceInbound Post QueueInbound Free QueueOutbound Post QueueOutbound Free QueueQueue for inbound messages from other processorswaiting to be processed by the Intel ® 80200processorQueue for empty inbound messages from the Intel ®80200 processor available for use by otherprocessorsQueue for outbound messages from the Intel ® 80200processor that are being posted to the otherprocessorsQueue for empty outbound messages from otherprocessors available for use by the Intel ® 80200processorWrittenReadReadWrittenThe two outbound queues allow the Intel ® 80200 processor to post outbound messages in onequeue and to receive free messages returning from the host processor. The Intel ® 80200 processorposts outbound messages, the host processor receives the posted message and when it is finishedwith the message, places it back on the outbound free queue for reuse by the Intel ® 80200processor.The two inbound queues allow the host processor to post inbound messages for the Intel ® 80200processor in one queue and to receive free messages returning from the Intel ® 80200 processor.The host processor posts inbound messages, the Intel ® 80200 processor receives the postedmessage and when it is finished with the message, places it back on the inbound free queue forreuse by the host processor.Developer’s Manual 6-7