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

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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	Virtex-7 Kintex-7
IP	MIG 7 Series

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