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AR# 16752

Virtex-II Pro RocketIO - ALIGN_COMMA_MSB can never be set to TRUE to override the default "FALSE." When can I use ALIGN_COMMA_MSB?

Description

I cannot set the ALIGN_COMMA_MSB attribute to TRUE to override the default "FALSE" setting. When can I use ALIGN_COMMA_MSB?

Solution

By default, ALIGN_COMMA_MSB is set to FALSE for all primitives except GT_CUSTOM, as the presence of a comma in the wrong byte lane will cause resynchronization. This causes the RXFIFO to reset, which ultimately leads to data loss.  

 

The purpose of ALIGN_COMMA_MSB is to align bytes into words in the FPGA fabric.  

 

As long as you ensure that you do not send commas in a byte lane other than the MSB, you can use the GT_CUSTOM primitive with ALIGN_COMMA_MSB set to TRUE.

AR# 16752
Date Created 09/03/2007
Last Updated 05/15/2014
Status Archive
Type General Article