Comment by TehCorwiz
1 day ago
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.
1 day ago
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.
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.
Yes, for exactly the reason. SDRAM is much easier to work with in retro computing than DDR.
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. :)
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