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AR# 46200

7 Series GTP/GTX/GTH - RXBYTEISALIGNED is not always reliable

Description

In some situations(e.g., low amplitude, long run lengths, or high frequencies), the RXBYTEISALIGNED signal might de-assert even when the received data is good and there is no change in the byte boundary. RXVALID can also be adversely affected by the OOB circuitry.

Solution

When the incoming amplitude is marginal, data has very long run lengths, or the line rate is high (above 5 Gb/s), the Out-of-Band (OOB) circuitry might not be completely reliable. The RXBYTEISALIGNED signal uses one of the outputs of the OOB block as one of its conditions, hence this signal might occasionally de-assert even when the received data is good and there is no change in the byte boundary.

For protocols with line rates above 5 Gb/s that do not use the OOB functionality, OOB block can decoupled from the RXBYTEISALIGNED signal with some caveats.

General ES and IES:

For applications with line rates above 5 Gb/s that do not require the OOB functionality, the OOB block should be decoupled from RXBYTEISALIGNED by driving RXELECIDLEMODE [1, 0] signals to 11. In this case, excessive noise in the system might occasionally look like a valid comma character when no valid data is present and cause a false assertion of RXBYTEISALIGNED. In such cases, a system level check should be in place to check the validity of data and byte alignment.

For those protocols in this frequency range that require the OOB functionality, OOB block cannot be decoupled from the RXBYTEISALIGNED signal. In this case, the RXBYTEISALIGNED signal might not be reliable after the first assertion.

If the OOB is not being used in production silicon, it can be powered downby setting PCS_RSVD_ATTR[8] to "0" and setting RXBUF_RESET_ON_EIDLE=FALSE.

Linked Answer Records

Associated Answer Records

Answer Number Answer Title Version Found Version Resolved
41613 7 Series FPGAs GTX/GTH Transceivers - Known Issues and Answer Record List N/A N/A
AR# 46200
Date Created 02/09/2012
Last Updated 02/14/2013
Status Active
Type General Article
Devices
  • Kintex-7
  • Virtex-7
  • Artix-7