[sdiy] FPGA

[Scott Gravenhorst]

James Elliott <johans121 at yahoo.com> wrote:
>Yea, I guess my initial post was a "little" nebulous. I sent that 
>email in desperation after many many hours of reading about AVRs 
>& FPGAs, specifically about how to integrate them with SDRAM. I 
>was looking at the 32bit AVRs and the Spartan 3 FPGAs (I even 
>spent a bit of time reading about the Parallax Propeller - I 
>don't know that I want to waste time learning a one-shot language 
>though). 
>
>
>As far as requirements are concerned I want to build a two voice 
>(at least) 16 or 24 bit sampler with a sampling rate of at least 
>44.1khz.I've already built 2 WTPA samplers, but quite frankly I 
>don't like them that much. Their noise floor problems renders 
>them almost useless for my needs. I understand a completely new 
>version is going to be released in the near future (I've been 
>following the discussions since it was first mentioned); however, 
>I really want to learn how to program embedded devices and I 
>figured I would *try* to kill 2 birds with one stone. My biggest 
>concern at this point is not necessarily in the programming but 
>in actually building a a complete "system", that is FPGA, clock, 
>ADC, DAC, inputs, outputs, memory. I have plenty of programming 
>experience, just not with embedded devices (outside of schoolwork 
>& a couple basic PIC programs for work work)... 
>
>Scott G, what Spartan 3 starter kit are you using and how did you 
>incorporate the ADC, DAC, and DDR SDRAM? Were those already on 
>the board or did you have to design your own circuit?? If you had 
>to design your own circuit, what devices did you use and do you 
>have any pointers (no pun intended)? 

14 bit ADC, 12 bit DAC and DDR SDRAM were already soldered to the board, so physical
integration wasn't a problem for me.

http://member.newsguy.com/~rhuang/FPGA/WideBus-Recorder.zip 

The above zip file contains a complete record and playback project using the
Spartan-3E Starter Kit board.  It uses the onboard DAC, ADC and DDR SDRAM.  Rick's
design implements everything on a wishbone bus.  I would think that this project is 
probably already most of what you need (except that you may want better DAC and ADC
parts).

What I did for my design was first to understand Rick's design, then I took it apart
(broke the wishbone so to speak) and rebuilt a simple, rather general purpose
handshake type interface to the SDRAM.

I don't do circuit boards, so I have no advice on that aspect.



>----- Original Message -----
>From: Scott Gravenhorst <music.maker at gte.net>
>To: synth-diy at dropmix.xs4all.nl
>Cc: 
>Sent: Thursday, October 27, 2011 6:49 AM
>Subject: Re: [sdiy] FPGA
>
>
>Eric Brombaugh <ebrombaugh1 at cox.net> wrote:
>>Of course it's feasible for some set of system specs 
>>(cost/complexity/sample length/sample rate/etc). What are your 
>>requirements? Scott Gravenhorst has been doing some work on 
>>SDRAM-based deep memory buffers using the Spartan 3E starter kit 
>>which would allow some fairly complex sampling. More than you're 
>>likely to get with any AVR out there at least. 
>>
>>Eric
>>
>>On Oct 26, 2011, at 9:22 PM, James Elliott wrote:
>>
>>> Would it be feasible to build a sampler with a FPGA? Or should 
>>I go AVR or ARM?????????????????????????? 
>
>I'm '' this close to a test of a looped delay effect using the DDR
>SDRAM on the Spartan-3E Starter Kit using an already developed FM bell
>synth as an audio source.  If I were to use the full RAM, several
>minutes of mono delay is possible (at the sample rate of about 65 kHz).
>This would mean several minutes of sample time on a sampler as well.
>
>In fact, the project that I used as a basis for my own was done by Rick
>Huang.  It is called the "widebus recorder" and is a sampler and
>playback design.  So it's really right there in his project.  All that
>is needed is an anti-alias filter on the input to the ADC.  I'm not
>sure why (but I may be about to find out) other than for longer record
>time, but Rick's design runs at a sample rate of 40 kHz.  I found the
>zip with Verilog source code using google.
>
>
>-- ScottG
>________________________________________________________________________
>-- Scott Gravenhorst
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-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- FPGA MIDI Synth Info: jovianpyx.dyndns.org:8080/public/FPGA_synth/
-- FatMan Mods Etc.: jovianpyx.dyndns.org:8080/public/fatman/
-- Some Random Electronics Bits: jovianpyx.dyndns.org:8080/public/electronics/
-- When the going gets tough, the tough use the command line.