In the simulation, the rx_phase_comp_fifo_error signal for Cyclone® IV GX devices will assert when there is a difference in frequency between the read and write clocks of the phase compensation FIFO. Once asserted, rx_phase_comp_fifo_error will remain asserted until rx_digital_reset is asserted.
However, if the read clock does not toggle in the simulation test bench, the rx_phase_comp_fifo_error signal will not assert. This does not match actual device behavior where rx_phase_comp_fifo_error will assert if the read clock is not toggling.
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