Altera RapidIO II MegaCore Function - Manual (Page 63)

Chapter 4: Functional Description 4–21
Logical Layer Interfaces
August 2014 Altera Corporation RapidIO II MegaCore Function
User Guide
IP Core Actions
In response to incoming Avalon-MM read requests to the I/O Logical layer Slave
module, the RapidIO II IP core generates read request packets on the RapidIO link, by
performing the following tasks:
■ For each incoming Avalon-MM read request, composes the RapidIO read request
packet
■ For each incoming Avalon-MM write request, composes the RapidIO write request
packet
■ Maintains status related to the composed packet to track responses:
■ Sends read request information to the Pending Reads buffer to wait for the
corresponding response packet
■ Sends NWRITE_R request information to the Pending Writes buffer to wait for
the corresponding response packet
■ Does not send SWRITE and NWRITE request information to the Pending Writes
buffer, because these transactions do not require a response to the user on the
I/O Logical layer Avalon-MM slave interface
■ Presents the composed packet to the Transport layer for transmission on the
RapidIO link
■ For each read response from the Transport layer, removes the original request
entry from the Pending Reads buffer and uses the packet’s payload to complete
the read transaction, by sending the read data on the Avalon-MM slave interface
■ For each write response from the Transport layer, removes the original request
entry from the Pending Writes buffer
1 At any time, the I/O Logical layer Slave module can maintain a maximum of eight
outstanding read requests and a maximum of eight outstanding write requests. The
module asserts the ios_rd_wr_waitrequest signal to throttle incoming requests above
the limit.
The RapidIO II IP core performs the following actions in response to each read request
transaction the I/O Logical layer Slave module processes:
■ If the IP core receives a read response packet on the RapidIO link, the read
operation was successful. After the I/O Logical layer Slave module receives the
response packet from the Transport layer, it passes the read response and data
from the Pending Reads buffer back through the Avalon-MM slave interface.
■ If the remote processing element is busy, the RapidIO II IP core resends the request
packet.
■ If an error or time-out occurs, the I/O Logical layer Slave module asserts the
ios_rd_wr_readresponse
signal on the Avalon-MM slave interface and captures
some information in the Error Management Extension registers.