I have a huge system generator core originally developed with 13.2 version. Actually we are updating some projects to the latest version of ISE, the 14.7.

In the final step we consolidate the project generated by SysGen, avoiding hierarchies and flattening and optimizing the design. This can be achieved with the -read_cores optimize xst option in command line mode, and the result is a unique optimized NGC file.

In 13.2 version this synthesis strategy give a result of 19% of occupancy, but in 14.7 the result is a 36%!!! of occupancy. I'm trying to change synthesis options to improve the result, without positive results...

Any idea about what have been changed between versions?

Best regards

  • \$\begingroup\$ A stupid remark: Could it be that it's optimizing "for speed" better in the recent version, thus using more resources available to it? \$\endgroup\$ – Dzarda May 4 '15 at 9:08
  • \$\begingroup\$ Hello Dzarda, it's possible, but trying Area strategies, the result is about the same. I don´t know if Matlab version could have any influence in the final result. \$\endgroup\$ – David Quiñones May 4 '15 at 10:46
  • \$\begingroup\$ I doubt Matlab is to blame. Can planAhead give you insights? I don't use System Generator, but I expect even a flatten hierarchy will show the Xilinx IP Cores as unflatten, planAhead should be able to give you resources utilization for each one. By comparing the netlist for both design, you may have a culprit! \$\endgroup\$ – Jonathan Drolet May 4 '15 at 13:24
  • \$\begingroup\$ @DavidQuiñones I faced similar behavior when compiled a single (complex) unit vs. several (up to all interesting) units into the selected (fixed) IC. It also depends on how many signals of the unit-under-test are routed out of the chip (i.e. connected to pins), because optimization (by default) eliminates no-load nets and registers. Maybe this is your case too. \$\endgroup\$ – asndre May 4 '15 at 16:26

Examining the resulting core with PlanAhead I have discovered that synthesis report files generated by XST synthesizer of 13.2 and 14.4 versions provide erroneous occupancy values.

This bug is resolved in 14.7 version and the real occupancy value is 36%. In fact, always have been 36%.

Jonathan, thank you for the advice of using PlanAhead!!

Best regards


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