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Last modification

• Rev 677 2012-02-21 16:01:04 GMT
• Author: stekern

• Log message:

  atlys: add 2-clock synchronizer chain for ddr2_calib_done
  
  The signal ddr2_calib_done signal comes from the ddr2 clock domain,
  while wb_req is treating it as if it came from wb_clk domain. As a
  result the timing analysis tool assumed a worst case scenario of 5ns
  between the two domains and the results were miserable.
  
  While we can argue that this is a multi-cycle path, the fact is that
  ddr2_calib_done feeds into multiple logic sinks and can potentially
  cause meta-stability issue in the design. The solution is to add a
  2-clock meta-stability filter to address both the timing problems and
  the meta-stability concern.
  
  Signed-off-by: Jason Zheng <jxzheng@gmail.com>
  Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
  Acked-by: Olof Kindgren <olof.kindgren@orsoc.se>