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[/] [openrisc/] [trunk/] [orpsocv2/] [boards/] [xilinx/] [atlys/] [rtl/] [verilog/] [xilinx_ddr2/] - Rev 868
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>