Altera RapidIO II MegaCore Function - Manual (Page 86)

4–44 Chapter 4: Functional Description
Logical Layer Interfaces
RapidIO II MegaCore Function August 2014 Altera Corporation
User Guide
Doorbell Module
The Doorbell module is an optional component of the I/O Logical layer. The Doorbell
module provides support for Type 10 packet format (DOORBELL class) transactions,
allowing users to send and receive short software-defined messages to and from other
processing elements connected to the RapidIO interface.
Figure 4–3 on page 4–7 shows how the Doorbell module is connected to the Transport
layer module. In a typical application the Doorbell module’s Avalon-MM slave
interface is connected to the system interconnect fabric, allowing an Avalon-MM
master to communicate with RapidIO devices by sending and receiving DOORBELL
messages.
When you configure the RapidIO II IP core, you can enable or disable the DOORBELL
operation feature, depending on your application requirements. If you do not need
the DOORBELL feature, disabling it reduces device resource usage. If you enable the
feature, a 32–bit Avalon-MM slave port is created that allows the RapidIO II IP core to
receive and generate RapidIO DOORBELL messages.
Doorbell Module Block Diagram
Figure 4–20 illustrates the Doorbell module. This module includes a 32–bit
Avalon-MM slave interface to user logic. The Doorbell module contains the following
logic blocks:
■ Register and FIFO interface that allows an external Avalon-MM master to access
the Doorbell module’s internal registers and FIFO buffers.
■ Tx output FIFO that stores the outbound DOORBELL and response packets waiting
for transmission to the Transport layer module.
■ Acknowledge RAM that temporarily stores the transmitted DOORBELL packets
pending responses to the packets from the target RapidIO device.
■ Tx time-out logic that checks the expiration time for each outbound Tx DOORBELL
packet that is sent.
■ Rx control that processes DOORBELL packets received from the Transport layer
module. Received packets include the following packet types:
■ Rx DOORBELL request.
■ Rx response DONE to a successfully transmitted DOORBELL packet.
■ Rx response RETRY to a transmitted DOORBELL message.
■ Rx response ERROR to a transmitted DOORBELL message.
■ Rx FIFO that stores the received DOORBELL messages until they are read by an
external Avalon-MM master device.
■ Tx FIFO that stores DOORBELL messages that are waiting to be transmitted.
■ Tx staging FIFO that stores DOORBELL messages until they can be passed to the Tx
FIFO. The staging FIFO is present only if you select Prevent doorbell messages
from passing write transactions
in the RapidIO II parameter editor.
■ Tx completion FIFO that stores the transmitted DOORBELL messages that have
received responses. This FIFO also stores timed out Tx DOORBELL requests.