How to add some SDRAM to a FPGA board ?

What kind of filter requires all the samples to be available in memory? Most DSP filters need only a sliding window of thousand samples, if at all. For such DSP filters without hardware multipliers, your 100MHz uC would not even match a 50MHz ARM.

The Apple II (and several of its descendents) did that as well. The good old days - when you could have RAM that was twice as fast as your processor! Apple did processor access on half the cycles, video (and implicit refresh) on the other half, and ended up running the CPU at a slightly odd frequency; so the video ran at the right rate. Approximately 1.023MHz, IIRC, a nice "even" divide by 14 off the

AFAIR I did not mention any filter. DSP is not only about filters. It's about ... well, processing signals, digitally. This goes well beyond the Laplace and Fourier transforms. And some applications need to remember samples from 30s before, not just the 1 or 2s of a digital reverberation chamber.

On top of that, I may end up teaming with musicians who are less technician than me, hence who have much more weird desires... since what matters is the final sounds, not how it's done. One of them uses 16 audio channels on stage, so this would leave only 2MB per channel if I had 32MB. That's not much room for long-term delays with high-quality samples.

Maybe I should have avoided the term DSP, even if I thought it was generic enough.

first, I am implementing a hardware multiplier in my uC. Ok it's only 8x8 unsigned but it will help is a few situations. But for "DSP work", I do my best to use adapted structures. I even have many unused DSP chips in stock (I was an ADi fan). And the "uC" has never been meant to be a workhorse, but rather a "controller" to a dedicated processing unit.

Furthermore, I don't understand why a second person raises the issue of "my 100MHz UC" (I presume it is a reference to YASEP). This was completely independent from the original question, and it might open a smelly can of worms... I'd rather work on it than speak about it.

Regards, yg

May be 60s, or 180s,... How do you draw the line? Why can't you store them in flash memory, SD or CF. Are they really so time critical?

You can move tens of MB per second with CF.

We are just echoing what you wrote on your site. OK, it is irrelevant in this case.

It depends on what is reasonably achievable and the compromises I can find. I have stocked many components for years and my original post came after an attempt to sort them. Now, I have tens of 32MB chips and they seem to fit, but I'm not (yet) confident with dynamic RAM.

First, it is not required to store the data when the system (which is not even defined) is off. If this was needed, I wouldn't limit the capacity to around 64MB, when 2BG is cheap.

Second, and that's what strikes me as really weird : Flash memory has a given endurance (in write cycles). It is well known that swap partitions should never go to a flash disk, for example. So if I use Flash memory to store a circular buffer of samples, the Flash device will suffer and fail after "some time" (depending on the controller, the Flahs, the access patterns, the temperature etc.).

Finally, time is obviously critical for real time sound processing, you don't want to hear "clicks". There's probably going to be many unpredictable/random accesses, and with roughtly 50KHz of sampling rate, 100ns of access time is OK but 1ms is not.

It's not so easy to make it work correctly. The fastest I have seen was around 8MB/s on a PC, IIRC. And a Flash device is not designed for constant writes.

regards,