Forums

I2S and ADSP21xx

Started by Vladimir Vassilevsky June 24, 2003
  
 I have to build an ADSP-218x based system with stereo codec. The codec
should have reasonable price (~$5) and performance (~80dB SNR). There
are many codecs of that kind available. All of them have I2S interface.
 
 Is there a simple and elegant way to interface I2S to ADSP-218x SPORT?


 Vladimir Vassilevsky, Ph.D.

 DSP and Mixed Signal Design Consultant

 http://www.abvolt.com
Vladimir Vassilevsky <vlv@abvolt.com> wrote in 
news:3EF87B84.CC21460D@abvolt.com:

> > I have to build an ADSP-218x based system with stereo codec. The codec > should have reasonable price (~$5) and performance (~80dB SNR). There > are many codecs of that kind available. All of them have I2S interface. > > Is there a simple and elegant way to interface I2S to ADSP-218x SPORT? > > > Vladimir Vassilevsky, Ph.D. > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.com >
You have several choices: 1. You could use an AC'97 codec if 48k sampling is sufficient. Our DSP- 8300 is based on a ADSP-2186M and uses this approach. (You might just want to use this product - check out our web site) 2. You can use an I2S codec that operates as an I2S master. In this case, you can configure the SPORT in multichannel mode and emulate an I2S interface. This interface is glueless. We use Wolfson WM8731 in this way. TI has a very similar part. 3. Many of the I2S codecs also support DSP interface modes. 4. You can use an I2S codec in slave mode but you need additional glue logic. I seem to recall that you just need a 7474 (to create the FS) and also use an additional port to determine phase. I haven't actually tried this method. -- Al Clark Danville Signal Processing, Inc. -------------------------------------------------------------------- Purveyors of Fine DSP Hardware and other Cool Stuff Available at http://www.danvillesignal.com

Al Clark wrote:
> > Vladimir Vassilevsky <vlv@abvolt.com> wrote in > news:3EF87B84.CC21460D@abvolt.com: > > > > Is there a simple and elegant way to interface I2S to ADSP-218x SPORT? > > > > You have several choices: > > 1. You could use an AC'97 codec if 48k sampling is sufficient. Our DSP- > 8300 > is based on a ADSP-2186M and uses this approach. (You might just want to > use this product - check out our web site)
That might be interesting. How much is it? What sample rates are supported? Is it WM8731 that you have onboard?
> 2. You can use an I2S codec that operates as an I2S master. In this case, > you can configure the SPORT in multichannel mode and emulate an I2S > interface. This interface is glueless. We use Wolfson WM8731 in this way. > TI has a very similar part.
My worries are that since only the RFS is used for frame sync in multiframe mode, that may cause timing problems between receive and transmit. Also, you have to set up the SPORT to 24 or 32 frames, and assert the RFS every two frames. Is it OK?
> 3. Many of the I2S codecs also support DSP interface modes.
That is interesting. Can you suggest one?
> 4. You can use an I2S codec in slave mode but you need additional glue > logic. I seem to recall that you just need a 7474 (to create the FS) and > also use an additional port to determine phase. I haven't actually tried > this method.
I was thinking to convert the protocols completely asynchronously with the help of EPLD, however it is rather heavy weight solution. Vladimir Vassilevsky, Ph.D. DSP and Mixed Signal Design Consultant http://www.abvolt.com
Vladimir Vassilevsky <vlv@abvolt.com> wrote in
news:3EF917B0.2D865C4C@abvolt.com: 

> > > Al Clark wrote: >> >> Vladimir Vassilevsky <vlv@abvolt.com> wrote in >> news:3EF87B84.CC21460D@abvolt.com: >> > >> > Is there a simple and elegant way to interface I2S to ADSP-218x >> > SPORT? >> > >> >> You have several choices: >> >> 1. You could use an AC'97 codec if 48k sampling is sufficient. Our >> DSP- 8300 >> is based on a ADSP-2186M and uses this approach. (You might just want >> to use this product - check out our web site) > > That might be interesting. How much is it? What sample rates are > supported? > Is it WM8731 that you have onboard?
We use a Wolfson WM9707, which has variable sampling rates of 48k, 44.1k, 22.05k, 16k, 11.025k & 8k There is a price schedule on our web site. Prices range from $200 to $125 ea. A dev kit is $250. http://www.danvillesignal.com
> >> 2. You can use an I2S codec that operates as an I2S master. In this >> case, you can configure the SPORT in multichannel mode and emulate an >> I2S interface. This interface is glueless. We use Wolfson WM8731 in >> this way. TI has a very similar part. > > My worries are that since only the RFS is used for frame sync in > multiframe mode, that may cause timing problems between receive and > transmit. Also, you have to set up the SPORT > to 24 or 32 frames, and assert the RFS every two frames. Is it OK?
The codec supplies the frame sync. For example, if the I2S interface assumes 32 bits for each sample, you can set up a four time slots of 16 bits each. Timing will be fine.
> >> 3. Many of the I2S codecs also support DSP interface modes. > > That is interesting. Can you suggest one?
The Wolfson and TI I mentioned in 2. are examples. You might check out Cirrus, Burr-Brown (TI), TI, AKM, ADI and Wolfson for additional candidates
> >> 4. You can use an I2S codec in slave mode but you need additional >> glue logic. I seem to recall that you just need a 7474 (to create the >> FS) and also use an additional port to determine phase. I haven't >> actually tried this method. > > I was thinking to convert the protocols completely asynchronously with > the help of EPLD, however it is rather heavy weight solution.
Thats why I prefer using the converter in master mode, although I still think it takes only a 7474. The frame sync is divided by 4 to create an I2S sync and you need to know which edge is the start of the I2S frame since the SPORT will not know.
> > Vladimir Vassilevsky, Ph.D. > > DSP and Mixed Signal Design Consultant > > http://www.abvolt.com >
-- Al Clark Danville Signal Processing, Inc. -------------------------------------------------------------------- Purveyors of Fine DSP Hardware and other Cool Stuff Available at http://www.danvillesignal.com