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the modelsim model seems to work slightly differently than the actual FPGA-based instantiation (shown with Signal Tap).
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Post your testbench, the testbench waveforms and your SignalTapII waveforms.
I've never had any issues with Modelsim vs SignalTap with the altsyncram component (except for the time I used a newer version of Modelsim-SE, rather than the Modelsim-ASE version shipped with Quartus). Though I've only ever used it in single-port or dual-port mode. Perhaps simple dual-port has an issue. You could try it in dual-port mode and see if that changes the results.
Cheers,
Dave
Honored Contributor
