ModelSim "True Dual Port" Memory viewer weird

Question

Hi everyone.

I have a question for you all.

I have a FPGA VHDL design using Cyclone III, in my design I used internal memory configured as true dual port RAM. I created the VHDL code, simulate it in ModelSim and waveform looks fine. But if I tried to view internal memory content, I found something weird. There are two memory list in memory list window, Port A memory and Port B memory. I can see the content of memory from Port A correctly but when I tried open window form Port B, all memory content become all "U".

I perform simulation to write memory through port B and read data written from Port A. Functional simulation show all fine. I just don't understand why memory viewer for Port B become all "U". Is there someone here know why this is happened? Is there something incorrect in my simulation or my design?

Thanks, any kind of help will be appreciated... :D

altera_forum · Answer

Are you of course reading port B after you've written it, right? In the meanwhile you're not writing the same location you're reading, true?

altera_forum · Answer

No, I write data into Port B, after writing sequence finished then I read data inside memory from Port A. So I don't read data being written in the same time.

Darkwave, do you have any idea?

thanks,...

altera_forum · Answer

I've not maybe understood the problem.

You told: "I write data into Port B, after writing sequence finished then I read data inside memory from Port A. So I don't read data being written in the same time." and before "I can see the content of memory from Port A" that is right since you're writing data on port B and reading from port A. Moreover there is no problem at all as you've stated..

What do you mean when you tell "when I tried open window form Port B"?

What are you using for simulate it?

Internal Quartus II simulator that is present until v9.1 or maybe Simulink with a vhdl/verilog testbench?

altera_forum · Answer

I wouldnt be surprised if it only used the port A storage - it is stored in a variable inside a process in the code. On the real hardware there is only 1 memory area for the two ports anyway. If "m_mem_data_b" is always 'U', it just means it is never assigned anything - if your design is working then Im presuming it only ever puts data into "m_mem_data_a". This models realistic behaviour.

if it works, dont worry.

altera_forum · Answer

Hi darkwave,

On ModelSim simulation window, on the left side, there is memory tab, it is internal memory viewer for simulation. On it's tab, there are two list, it is m_mem_data_a (for port A) and m_mem_data_b(for port B ), when I said "I tried open window form Port B" I mean I clicked the m_mem_data_b so a windows displaying the content of internal memory appear.

I use ModelSim with VHDL testbench.

Hi Tricky,

So It is for modeling only. Now I don't worry again.

Anyway, Thanks for both of you. I appreciate all of your help...:) :) :)

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ModelSim "True Dual Port" Memory viewer weird

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