RapidIO Intel FPGA IP User Guide

ID 683884
Date 9/15/2021
Public
Document Table of Contents

4.3.4. 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 5-bit CRC to cover the 19-bit symbol and appends the CRC at the end of the symbol
  • Transmits an idle 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.

In 1.25, 2.5, and 3.125 Gbaud variations, the internal transmitters are not turned off while the initialization state machine is in the SILENT state. Instead, while in SILENT state, the transmitters send a continuous stream of K28.5 characters, all of the same disparity. This behavior causes the receiving end to declare numerous disparity errors and to detect a loss of lane_sync as intended by the specification.

In 5.0 Gbaud variations, the internal transmitters are turned off while the initialization state machine is in the SILENT state. This behavior also causes the link partner to detect the need to reinitialize the RapidIO link.