Altera RapidIO II MegaCore Function - Manual (Page 117)

Chapter 4: Functional Description 4–75
Physical Layer
August 2014 Altera Corporation RapidIO II MegaCore Function
User Guide
CRC Checking and Removal
The Physical layer checks the CRC bits in an incoming RapidIO packet and flags CRC
and packet size errors. It strips all CRC bits and padding bytes from the data it sends
to the Transport layer.
Low-Level Interface Transmitter
The transmitter in the low-level interface transmits output to the RapidIO interface.
This module performs the following tasks:
■ Assembles packets and control symbols into a proper output format
■ Generates the 13-bit CRC to cover the 35-bit symbol and appends the CRC at the
end of the symbol
■ Transmits an IDLE2 sequence during port initialization and when no packets or
control symbols are available to transmit
■ Transmits outgoing multicast-event control symbols in response to user requests
■ Transmits status control symbols and the rate compensation sequence periodically
as required by the RapidIO specification
The low-level transmitter block creates and transmits outgoing multicast-event
control symbols. Each time the multicast_event_tx input signal changes value, this
block inserts a multicast-event control symbol in the outgoing bit stream as soon as
possible.
The internal transmitters are turned off while the initialization state machine is in the
SILENT state. This behavior causes the link partner to detect the need to reinitialize
the RapidIO link.
The transmitter transceiver is an embedded Native PHY IP core.
The Physical layer ensures that a maximum of 63 unacknowledged packets are
transmitted, and that the ackIDs are used and acknowledged in sequential order. To
support retransmission of unacknowledged packets, the Physical layer maintains a
copy of each transmitted packet until the packet is acknowledged with a
packet-accepted
control symbol.
The RapidIO II IP core supports receiver-controlled flow control in both directions.
If the receiver detects that an incoming packet or control symbol is corrupted or a link
protocol violation has occurred, the Physical layer enters an error recovery process. In
the case of a corrupted incoming packet or control symbol, and some link protocol
violations, the transmitter sends a packet-not-accepted symbol to the sender. A
link-request
link-response control symbol pair is then exchanged between the link
partners and the sender then retransmits all packets starting from the ackID specified
in the link-response control symbol. The transmitter attempts the link-request
link-response
control symbol pair exchange seven times. If the protocol and control
block times out awaiting the response to the seventh link-request control symbol, it
declares a fatal error.
When a time-out occurs for an outgoing packet, the Physical layer starts the recovery
process. If a packet is retransmitted, the time-out counter is reset.