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AR# 36195

MIG v3.4 Virtex-6 DDR2 - Unroute errors occur on dqs_p_iodelay due to Map option

Description

When targeting a MIG Virtex-6 DDR2 core and the MAP optimization option is changed to "SPEED", unroute warnings similar to the following occur in PAR:

2 signals are not completely routed.
WARNING:ParHelpers:360 - Design is not completely routed.
u_memc_ui_top/u_mem_intfc/phy_top0/u_phy_data_io/gen_dqs[0].u_phy_dqs_iob/dqs_p_iodelay
u_memc_ui_top/u_mem_intfc/phy_top0/u_phy_data_io/gen_dqs[1].u_phy_dqs_iob/dqs_p_iodelay


Solution

The problem is that the connectivity in the actual IOB site changes depending on whether "-global_opt" is used or not.

When running "-global_opt OFF" (the default used by MIG), the I/O site is set to "IOBM" type and contains routes to the N pair (inside the IOB). 

However, if "-global_opt Area/Speed/Power" is used, the I/O site changes to "IOB" type and does not contain any physical routes to the N pair.

This results in an unroutable situation.

To work around this, the "S" constraint (save constraint) can be added in the UCF similar to the following:
 

NET "u_memc_ui_top/u_mem_intfc/phy_top0/u_phy_data_io/gen_dqs[0].u_phy_dqs_iob/u_iobuf_dqs/split_buf_net" S;
NET "u_memc_ui_top/u_mem_intfc/phy_top0/u_phy_data_io/gen_dqs[1].u_phy_dqs_iob/u_iobuf_dqs/split_buf_net" S;


Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
34587 MIG v3.4 - Release Notes and Known Issues for ISE Design Suite 12.1 N/A N/A
AR# 36195
Date Created 06/13/2010
Last Updated 09/03/2014
Status Active
Type Known Issues
Devices
  • Virtex-6 CXT
  • Virtex-6 HXT
  • Virtex-6 LX
  • More
  • Virtex-6 LXT
  • Virtex-6 SXT
  • Less
IP
  • MIG