Dual-Port RAM Simulation in ModelSim

I'm trying to simulate dual-port RAM using a shared variable in ModelSim
6.1b.

When I isolate the dual-port RAM in its own test bench the behavior is
correct. However, when incorporated into my larger design the behavior
is strange. For instance, the stored data does not appear at the
data_out port until the first cycle the (registered) address changes.

Has anyone experienced this problem? Could this be a bug in ModelSim?

Thanks,
Keith

Keith Blankenship

Keith Blankenship wrote:
> I'm trying to simulate dual-port RAM using a shared variable in ModelSim
> 6.1b.

Are you using a block ram code template
provided by the fpga vendor? I don't recall
any such template that uses a shared variable.

> For instance, the stored data does not appear at the
> data_out port until the first cycle the (registered) address changes.

That sounds normal for block ram.

> Could this be a bug in ModelSim?

Very unlikely.

-- Mike Treseler

Mike Treseler