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AR# 57399

Spartan-6 - LogiCORE IP DisplayPort v3.2 - VESA Specification Termination Scheme Causes Corruption on the AUX State Machine


Version Found: v3.2
Version Resolved and other Known Issues: See (Xilinx Answer 33258).

The VESA DisplayPort specification requires that when the AUX channels are not driven, the differential pairs (P and N) should be terminated/pulled to a common voltage reference point.
This termination scheme causes Spartan-6 I/O to generate internal "noise" that could exceed 0.4 us Unit Interval and will penetrate the soft AUX noise filter that was added in v3.2 Rev 2 core (Xilinx Answer 55359). Due to the length of the "noise" being very similar to the regular data length, having the AUX noise filter alone will not be sufficient.

When AUX transaction started, it will always be preceded by a SYNC word which is 26 to 32 consecutive transitions followed immediately by 2 us high and 2 us low.
It was found that the DisplayPort v3.2 core did detect the SYNC word but did not look for consecutive transitions, therefore noises that penetrate through the AUX noise filter can inadvertently advance the state machine.


The DisplayPort v3.2 Rev 8 and later patch includes an updated AUX state machine for both the source and sink core.  The updated AUX state machine will look specifically for 26 to 32 consecutive transitions in the SYNC word followed by the START code (2 us high and 2 us low).  The AUX transaction will be processed by the core after a successful SYNC word has been detected.

For 7 series devices, it is recommended to upgrade to the latest core release available in Vivado tool. This issue was resolved in the DisplayPort v4.1 core.

The DisplayPort v3.2 patch can be found in (Xilinx Answer 53422).
Source core should be at revision 4 or later.
  i.e. The VERSION_REGISTER (0x0F8) should read 03020400.

Sink core should be at revision 8 or later.
  i.e. The VERSION_REGISTER (0x0F8) should read 03020800.

Revision History:
9/9/2013 - Initial Release

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AR# 57399
Date 09/10/2013
Status Active
Type General Article
  • Spartan-6
  • DisplayPort