2.5.1. Metaframe Format and Framing Layer Control Word
The Enhanced PCS supports programmable metaframe lengths from 5 to 8192 words. However, for stability and performance, Intel recommends you set the frame length to no less than 128 words. In simulation, use a smaller metaframe length to reduce simulation times. The payload of a metaframe could be pure data payload and a Burst/Idle control word from the MAC layer.
The framing control words include:
- Synchronization (SYNC)—for frame delineation and lane alignment (deskew)
- Scrambler State (SCRM)—to synchronize the scrambler
- Skip (SKIP)—for clock compensation in a repeater
- Diagnostic (DIAG)—provides per-lane error check and optional status message
To form a metaframe, the Enhanced PCS frame generator inserts the framing control words and encapsulates the control and data words read from the TX FIFO as the metaframe payload.
The DIAG word is comprised of a status field and a CRC-32 field. The 2-bit status is defined by the Interlaken specification as:
- Bit 1 (Bit 33): Lane health
- 1: Lane is healthy
- 0: Lane is not healthy
- Bit 0 (Bit 32): Link health
- 1: Link is healthy
- 0: Link is not healthy
The tx_enh_frame_diag_status[1:0] input from the FPGA fabric is inserted into the Status field each time a DIAG word is created by the framing generator.