How to implement DE0 SDRAM as 2-port RAM

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I began writing the simulation but when I wen to test it in modelsim, modelsim reported that it only supports one HDL. Since some of the files are verilog (generated by QSYS) it won't allow simulation.

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Qsys has an option to set the simulation language to VHDL. Did you try it? There's no guarantee that it will work though, since not all Altera IP is provided in both languages.

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I did get the SDRAM working but the display is mostly noise. I can tell it is somewhat working because the general color of the noise changes predictably as I aim the camera from a dark area to a bright area. The noise is likely because of issues with two masters fighting for access to the SDRAM chip. Also the sdram_controller_s1_waitrequest signal seems to be always high.

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That does not sound like its "working" at all.

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1. Is there possibly a required init period that I'm not allowing time for?

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No idea. Did you look at the DE0 example designs provided with the kit?

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2. Is there a better way to delegate access to the SDRAM chip than what I'm doing below? Maybe alternate every other clock cycle?

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You'll need to check that your code implements an Avalon-MM master correctly. Read/write transactions need to be asserted until wait-request deasserts.

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The SDRAM chip is made by ISSI. The pdf for this specific chip states that the acceptable clock frequencies are 133, 143, 166, & 200MHz. The altera tutorials that involve sdram instruct you to create a ALTPLL with a 50mhz output and a -3ns phase shift for the SDRAM. I was using a 100Mhz PLL with a -3ns phase shift. I'll try other frequencies.

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The phase-shift is board-specific. I think I wrote some notes in the DE0-nano SDRAM tutorial. I performed a TimeQuest timing and adjusted the clock phase until it provided suitable timing margin.

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3. Do you know what frequency I should be using? The information seems to be conflicting.

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100MHz should be fine. Start with that, and then once it works, you should have a better understanding of what it takes to get it to operate at a different frequency.

Cheers,

Dave