Doesn’t DDR just stand for Double-Data-Rate? So you implemented basic DDR on top is sdram. Not a bad approach, just wanted to point it out.

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robinsonb5 3 days ago | parent [-]

It does, yes. But the DDR RAM available on the target board is DDR3 which is actually quite inconvenient for retro projects for a number of reasons.

Quite apart from the increased complexity, the most important difference is that there's a minimum speed as well as a maximum speed for modern DDR RAM, which means there's usually quite a narrow window of achievable clock rates when getting an FPGA to talk to DDR3.

I suspect that's why the author chose to use the DDR for video: It's usually easy to keep plain old SDRAM in lockstep with a soft-CPU, since you can run it at anything between 133MHz (sometimes even more) and walking pace, so there's no need to deal with messy-and-latency-inducing clock domain crossing.

Streaming video data in bursts into a dual-clock FIFO and consuming it on the pixel clock is a much more natural fit.

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nand2mario 3 days ago | parent [-]

Yes, for exactly the reason. SDRAM is much easier to work with in retro computing than DDR.

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accrual 3 days ago | parent | next [-]

My first DDR system, an Athlon XP, feels like a very different beast than my 440BX with SDRAM despite being only a couple years newer. :)

	▲	anthk 3 days ago \| parent [-]
		I had that with a Geforce2. Or was Athlon 2000. Wait, Athlon 2000 at 1666 MHZ, really fast until the capacitors on a Gigayte motherboard blew up.

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38 3 days ago | parent | prev [-]

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