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Old 26th February 2014, 07:37 PM   #181
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Quote:
Originally Posted by syklab View Post
I just got a BBB delivered yesterday and have been looking around on how to get I2S output from it, I haven't seen any new release from Volumio which might address the I2s payback for BBB yet, is it coming soon? Any hint from expert?
Its already possible to get music out of the BBB via I2S, I have had it running using the latest Debian Wheezy OS using FFMPEG. Also had music using Volumio tho I did have a problem with distortion on one channel. However there are issues with resampling to 48khz (and possibly other issues) which need addressing before its a fully working solution. As above a few people looking into it on different forums. Rune Audio also looking to get a new relase with I2S support but I don't think they will have the 48khz issues sorted. I wish I could contribute but I am hitting the limits of my knowledge!

I also have a Raspberry Pi running fine via I2S but really want to get the BBB going - better platform or our needs.

Puting my hopes on Russ to get this one sorted
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Old 27th February 2014, 11:23 AM   #182
miero is offline miero  Czech Republic
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BBB has 24.576MHz oscillator only. It allows to generate 48000Hz and its multiples. See the figure 45. in the BBB_SRM.pdf.

It seems that cape could add another oscillator for 44100Hz frequencies and route it to the same pin.

And switch between them via oscillator OutputEnable control pins.
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Old 27th February 2014, 12:54 PM   #183
tunasto is offline tunasto  Netherlands
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BBB is supposed to play 32bit/128khz over SPDIF.
Formula for oscilator freq is:

32bit * 2 channel * 2(slots) = 128

128 * 192khz = 24.576 Mhz

For I2s, there is no 2 slots only one, so formula is 64 * fs, which is 32bit/384khz with 24Mhz oscilator


Regards,

Denis
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Old 27th February 2014, 07:04 PM   #184
glt is offline glt  United States
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Quote:
Originally Posted by miero View Post
BBB has 24.576MHz oscillator only. It allows to generate 48000Hz and its multiples. See the figure 45. in the BBB_SRM.pdf.

It seems that cape could add another oscillator for 44100Hz frequencies and route it to the same pin.

And switch between them via oscillator OutputEnable control pins.
It seems that way. Also the processor only has two integer coefficients for clock division, so there is no way to generate the 44.1K clocks from the on-board clocks.
A cape with two clocks, clean power supplies and connectors for I2S would be a good starting point... (and the drivers that would take advantage of these clocks)
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Last edited by glt; 27th February 2014 at 07:07 PM.
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Old 27th February 2014, 08:01 PM   #185
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Thanks, that greatly improves my understanding of the issue.

Looking at the RaspberryPi I see 2 oscillators with frequencies 25.000 and 19.20 stamped on them. So, unless these aren't the actual frequencies, how would that be working?
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Old 27th February 2014, 08:30 PM   #186
miero is offline miero  Czech Republic
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Originally Posted by ChrisMmm View Post
Looking at the RaspberryPi I see 2 oscillators with frequencies 25.000 and 19.20 stamped on them. So, unless these aren't the actual frequencies, how would that be working?
It might play at the closest frequency to 44100 it can generate, e.g.:

25000000 / 567 = 44091.71Hz
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Old 28th February 2014, 03:14 AM   #187
DQ828 is offline DQ828  Australia
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Is it possible to have the BBB control the TP DAC just like you have done with your code & the Arduino?

My ideal would be to recreate your software for this application & then add other functionality, like the music streaming & control.
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Old 28th February 2014, 06:25 AM   #188
glt is offline glt  United States
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Sure. You just have to learn the environment and write/port the code :-)
But an Arduino is only $10 nowadays and the programming environment is much simpler.
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Old 28th February 2014, 08:58 AM   #189
DQ828 is offline DQ828  Australia
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Originally Posted by glt View Post
Sure. You just have to learn the environment and write/port the code :-)
But an Arduino is only $10 nowadays and the programming environment is much simpler.
Yer, I'm sure the whole code thing would be a bridge too far.
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Old 28th February 2014, 09:40 PM   #190
glt is offline glt  United States
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It is definite that BBB cannot support 44.1KHz and family. See page 75 of the System manual: https://github.com/CircuitCo/BeagleB...M.pdf?raw=true

There is a 24.576 MHz connected to the Audio subsystem in order to generate the audio frequencies.

Fortunately, this is also connected to an expansion pin (GPIO3_21) and the oscillator can be disabled in s/w. For now the only way for bit perfect output is through USB.
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