Altera RapidIO MegaCore Function - Manual (Page 87)

Chapter 4: Functional Description 4–41
Logical Layer Modules
August 2014 Altera Corporation RapidIO MegaCore Function
User Guide
Input/Output Avalon-MM Slave Module
The I/O Avalon-MM slave Logical layer module transforms Avalon-MM transactions
to RapidIO read and write request packets that are sent through the Transport and
Physical layer modules to a remote RapidIO processing element where the actual read
or write transactions occur and from which response packets are sent back when
required. Avalon-MM read transactions complete when the corresponding response
packet is received.
Figure 4–21 on page 4–42 shows a block diagram of the I/O
Avalon-MM Logical layer slave module and its interfaces.
1 The I/O Avalon-MM slave module is referred to as a slave module because it is an
Avalon-MM interface slave.
1 The maximum number of outstanding transactions (I/O Requests) supported is 26 (14
read requests + 12 write requests).
To maintain full-duplex bandwidth, two independent Avalon-MM interfaces are used
in the I/O slave module—one for read transactions and one for write transactions.
When the read Avalon-MM slave creates a read request packet, the request is sent to
both the Pending Reads buffer to wait for the corresponding response packet, and to
the read request transmit buffer to be sent to the remote processing element through
the Transport layer. When the read response is received, the packet’s payload is used
to complete the read transaction on the read Avalon-MM slave.
For a read operation, one of the following responses occurs:
■ The read was successful. After a response packet is received, the read response
and data are passed from the Pending Reads buffer back through the read
Avalon-MM slave interface.
■ The remote processing element is busy and the request packet is resent.
■ An error or time-out occurs, which causes io_s_rd_readerror to be asserted on
the read Avalon-MM slave interface and some information to be captured in the
Error Management Extension registers.
How the write request is handled depends on the type of write request sent. For
example, unlike a read request, not all write requests send tracking information to the
Pending Writes buffer. NWRITE and SWRITE requests do not send write tracking
information to the Pending Writes buffer. Only write requests such as NWRITE_R, that
require a response, are sent to both the Pending Writes and Transmit buffers. Write
requests are sent through the Transport and Physical layers to the remote processing
element.