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  3. AR# 53436: MIG 7 Series RLDRAM II - Timing failure from CMD_WR_EN to PRE_FIFO

AR# 53436

MIG 7 Series RLDRAM II - Timing failure from CMD_WR_EN to PRE_FIFO

Description

Version Found: v1.8
Version Resolved and other Known Issues: See (Xilinx Answer 45195)

When implementing the MIG 7 Series RLDRAM II v1.8/v1/8a design, the following timing violations may be seen between the CMD_WR_EN and PRE_FIFO.

Slack (setup path):     -0.479ns (requirement - (data path - clock path skew + uncertainty))

  Source:               u_mig_7series_v1_8/u_mig_7series_v1_8_rld_memc_ui_top_std/u_rld_phy_top/u_phy_write_top/GEN_PHY_CNTRL_INIT.u_qdr_rld_phy_cntrl_init/of_cmd_wr_en (FF)
  Destination:          u_mig_7series_v1_8/u_mig_7series_v1_8_rld_memc_ui_top_std/u_rld_phy_top/u_qdr_rld_mc_phy/qdr_rld_phy_4lanes_0.u_qdr_rld_phy_4lanes/qdr_rld_byte_lane_D.qdr_rld_byte_lane_D/GEN_PRE_FIFO.u_qdr_rld_pre_fifo/_o32462_48 (FF)

  Requirement:            4.444ns
  Data Path Delay:      4.288ns (Levels of Logic = 3)
  Clock Path Skew:     -0.564ns (1.364 - 1.928)
  Source Clock:          clk rising at 0.000ns
  Destination Clock:    clk rising at 4.444ns
  Clock Uncertainty:    0.071ns  ((TSJ^2 + DJ^2)^1/2) / 2 + PE
    Total System Jitter (TSJ):  0.070ns
    Discrete Jitter (DJ):           0.123ns
    Phase Error (PE):              0.000ns

 

Solution

These timing failures can occur as a result of too high a fan-out on the "of_cd_wr_en" and "of_data_wr_en" registers within the qdr_rld_phy_cntrl_init.v module. 

If these timing failures are seen, the following changes can be made to qdr_rld_phy_cntrl_init.v as a work-around:

Change:

  output reg         of_cmd_wr_en,
  output reg         of_data_wr_en

to:

  (* keep = "true", max_fanout = 10 *)  output reg         of_cmd_wr_en /* synthesis syn_maxfan = 10 */ ,
  (* keep = "true", max_fanout = 10 *)  output reg         of_data_wr_en/* synthesis syn_maxfan = 10 */

Revision History
12/18/2012 - Initial release

Linked Answer Records

Master Answer Records

Answer Number Answer Title Version Found Version Resolved
45195 MIG 7 Series - Release Notes and Known Issues for All ISE versions and Vivado 2012.4 and older tool versions N/A N/A
AR# 53436
Date 01/26/2015
Status Active
Type Known Issues
Devices
IP