Arria® V Device Handbook: Volume 2: Transceivers

ID 683573
Date 5/29/2020
Public
Document Table of Contents

1.2.2.1.2. Bit-Slip Mode

In bit-slip mode, the word alignment is achieved by manually controlling the data slip with the rx_std_bitslip signal.

Slipping the received data by one bit effectively shifts the word boundary by one bit. You can implement a controller in the FPGA fabric to iteratively control the rx_std_bitslip signal until the word aligner output matches the predefined word alignment pattern to achieve synchronization.

Table 25.  Word Aligner in Bit-Slip Mode
PCS Mode PMA–PCS Interface Width (bits) Word Alignment Operation
Single Width 8
  1. At every rising edge to the rx_std_bitslip signal, the word aligner slips one bit into the received data.
  2. When bit-slipping shifts a complete round of the data bus width, the word boundary is back to the original boundary.
  3. Check the received data, rx_parallel_data after every bit slip operation whether the predefined word alignment pattern is visible in the new word boundary. When the word alignment pattern is visible in the new word boundary, the alignment process is completed and the bit-slip operation can be stopped.
10
Double Width 16
20
Note: For every bit slipped in the word aligner, the earliest bit received is lost.

For this example, consider that 8'b11110000 is received back-to-back and 16'b0000111100011110 is the predefined word alignment pattern. A rising edge on the rx_std_bitslip signal at time n + 1 slips a single bit 0 at the MSB position, forcing the rx_parallel_data to 8'b01111000. Another rising edge on the rx_std_bitslip signal at time n + 5 forces rx_parallel_data to 8'b00111100. Another rising edge on the rx_std_bitslip signal at time n + 9 forces rx_parallel_data to 8'b00011110. Another rising edge on the rx_std_bitslip signal at time n + 13 forces the rx_parallel_data to 8'b00001111. At this instance, rx_parallel_data in cycles n + 12 and n + 13 is 8'b00011110 and 8'b00001111, respectively, which matches the specified 16-bit alignment pattern 16'b0000111100011110.

Figure 29. Word Aligner Configured in Bit Slip Mode


Note: Bit slip operation can also be triggered by a 0 to 1 transition in the rx_bitslip register.