Stratix V Device Handbook: Volume 2: Transceivers

ID 683779
Date 11/23/2021
Public
Document Table of Contents

4.3.2. Supported Features

The Interlaken protocol supports a number of framing layer functions. The functions are defined in the Interlaken Protocol Definition, Rev 1.2.
Table 33.  Supported Features in Interlaken Configuration
Feature Supported
Metaframe generation and payload insertion Yes
Block synchronization (word alignment) and metaframe synchronization (frame synchronization) Yes
64B/67B framing Yes
±96 bits disparity maintenance Yes
Frame synchronous scrambling and descrambling Yes
Diagnostic word generation Yes
Framing Layer Control Word Forwarding Yes
CRC-32 generation and checking of lane data integrity Yes
Multi-lane deskew alignment No
Transmit and receive FIFO backpressure control and handshake Yes

Block Synchronizer

The block synchronizer in the receiver PCS achieves and maintains a 64B/67B word boundary lock. This block searches for valid synchronization header bits within the data stream and achieves lock after 64 consecutive legal synchronization patterns are found. After a 64B/67B word boundary lock is achieved, the block synchronizer continuously monitors and flags for invalid synchronization header bits. If 16 or more invalid synchronization header bits are found within 64 consecutive word boundaries, the block synchronizer deasserts the lock state and searches again for valid synchronization header bits.

The block synchronizer implements the flow diagram shown in Figure 13 of Interlaken Protocol Definition v1.2 and provides the word lock status to the FPGA fabric.

64B/67B Frame Generator

The transmit frame generator implements 64B/67B encoding, as explained in Interlaken Protocol Definition v1.2. The Interlaken metaframe generator synchronously generates the framing layer control words, frame synchronizer, scrambler state, skip words, and diagnostic word, and maps the transmitter data into the payload of the metaframes. The metaframe length is programmable from 5 to a maximum value of 8191, 8-byte words.

Note: Ensure that the metaframe length is programmed to the same value for both the transmitter and receiver.

Frame Synchronizer

The receive frame synchronizer delineates the metaframe boundaries and searches for each of the framing layer control words: Synchronization, Scrambler State, Skip, and Diagnostic. When four consecutive synchronization words have been identified, the frame synchronizer achieves the frame locked state. Subsequent metaframes are then checked for valid synchronization and scrambler state words. If four consecutive invalid synchronization words or three consecutive mismatched scrambler state words are received, the frame synchronizer loses frame lock. In addition, the frame synchronizer provides a receiver metaframe lock status to the FPGA fabric.

Running Disparity

The disparity generator inverts the sense of bits in each transmitted word to maintain a running disparity of ± 96 bit boundary. It supplies a framing bit in bit position 66 as explained in Table 4 of Interlaken Protocol Definition Revision 1.2. The framing bit enables the disparity checker to identify whether bits[63:0] for that word are inverted.

Frame Synchronous Scrambling/Descrambling

The scrambler/descrambler block in the transmitter/receiver PCS implements the scrambler/descrambler polynomial x58 + x39 + 1 per Interlaken Protocol Definition Revision 1.2. Synchronization and Scrambler State Words, as well as the 64B/67B framing bits are not scrambled/descrambled. The Interlaken PHY IP core automatically programs random linear feedback shift register (LFSR) initialization seed values per lane.

The receiver PCS synchronizes the scrambler with the metaframe as described in the state flow shown in Figure 1 of Interlaken Protocol Definition Revision 1.2.

The frame synchronizer features a whole set of error and performance monitoring ports to the FPGA fabric interface and register status bits when using the Avalon® Memory-Mapped Management Interface. A receiver ready port, frame lock status, and cyclic redundancy check (CRC)-32 error detection port is available to the FPGA fabric. The Avalon Memory-Mapped Management Interface provides additional functionality with word boundary lock, frame lock status, synchronization word error detection, scrambler mismatch error, and CRC-32 error detection status register bits.

Skip Word Insertion

The frame generator generates the mandatory fixed location skip words with every metaframe following the scrambler state word and generates additional skip words based on the transmitter FIFO capacity state.

Skip Word Deletion

The frame synchronizer does not delete skip words. Instead, the frame synchronizer forwards the skip words it receives to the MAC layer so the MAC can maintain and perform deskew alignment.

Diagnostic Word Generation and Checking of Lane Data Integrity (CRC-32)

The CRC-32 generator calculates the CRC for each metaframe and appends it to the diagnostic word of the metaframe. An optional CRC-32 error flag is also provided to the FPGA fabric.

Framing Layer Control Word Forwarding

The four metaframe framing layer control words-Synchronization, Scrambler State, Skip, and Diagnostic Words-are not deleted but forwarded to the MAC layer. This action enables the MAC layer to employ multi-lane deskew alignment within the FPGA fabric.
Note: The Scrambler State word seed is zeroed (Bit[57:0]) before it is forwarded to the MAC layer.

Multi-Lane Deskew Alignment

The Interlaken PHY IP does not support multi-lane deskew alignment. You must implement the multi-lane deskew alignment state machine in the core fabric or the Interlaken Intel® FPGA IP core function within the FPGA fabric.

Transmit and Receive FIFO Control and Status

The Interlaken PCS configures the transmit and receive FIFOs in elastic buffer mode. In this mode of operation, a lane synchronization, backpressure and FIFO control, and status port signals are provided to the MAC layer for handshaking.

Transceiver Multi-Lane Bonding and Transmit Skew

A soft-bonding IP is used for Interlaken bonding in the transceivers. The transceiver clocking in each lane is configured as non-bonded. For multi-lane designs, a dedicated PLL reference clock pin that is equidistant from the transmit PLLs in each bank must be selected. You must tightly match lane board traces to minimize lane-to-lane skew.

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