MPC8540 datasheet(1043/1302 Pages) FREESCALE

1043 / 1302 page

RapidIO Message Unit

MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

Freescale Semiconductor

17-119

17.8.4.3.4 Data Message Controller Limitations and Restrictions

This section describes some of the limitations and restrictions of the data message controller. This

is intended to help software maximize the message passing performance and avoid programming

errors.

Software must guarantee that the enqueue pointer is not pointing to an invalid descriptor in

chaining mode if the enqueue and dequeue pointers are not equal.

17.8.4.4 Doorbell Message Controller

The RapidIO protocol supports a doorbell message type that contains no data payload. Even

though the RapidIO architecture references outbound and inbound doorbell message controllers,

the RapidIO controller supports only an inbound doorbell message queue. Outbound doorbells are

generated outside RapidIO within the outbound ATMU. Inbound doorbell messages are handled

by the doorbell message controller similar to how the data message controller handles inbound

data messages. The doorbell controller receives the doorbell message and places it in a circular

queue located in the local memory.

Figure 17-85 shows an example of the structure of the inbound doorbell queue and its pointers.

The doorbell queue of the RapidIO controller has eight entries, three of which are currently valid.

The doorbell controller adds doorbell information to the head of the queue and the processor core

removes it from the tail.

The doorbell entry size is fixed at 64 bits because doorbell packets only pass a small amount of

information, making the enqueue and dequeue pointers double-word addresses.

Figure 17-85. Inbound Doorbell Queue and Pointer Structure

Doorbell

Entry

Doorbell

Entry

Doorbell

Entry

Enqueue pointer

Dequeue pointer

Processor Core Read

Inbound

Doorbell

Controller

Local Memory

Packets from

RapidIO interface

MPC8540 Datasheet(PDF) 1043 Page - Freescale Semiconductor, Inc