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Old 11th January 2013, 01:41 AM   #2051
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there's no instruction needed; nothing pi specific, that is. the shipped kernel has uac2 support just fine.

some hubs do not pass audio thru (linux hub topology bug of some kind, on some usb1 or usb2 hubs). just connect AW direct to usb port on the pi. make sure the pi has enough stable 5v power! you are powering the AW thru the pi.

alsa just plain works. most of us run MPD and that just plain works.

wired ethernet (avoid wireless), usb AW on one usb port and I leave the other one free. that gives a pretty reliable config.
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Old 11th January 2013, 01:47 AM   #2052
nikkov is offline nikkov  Russian Federation
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Quote:
Originally Posted by linuxworks View Post
there's no instruction needed; nothing pi specific, that is. the shipped kernel has uac2 support just fine.
I bought R-Pi without SD card and don't know which image select for guaranteed working with UAC2. Sorry, I'm not linux user
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Old 11th January 2013, 05:08 AM   #2053
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its safe to get the latest released raspian. there was one from the middle of december, that's what I used. that should be good; and if there is newer, so much the better.

I can't be sure that the 'usb elephant' bug has been fixed, but I have not noticed any -traffic- based lockups. insert/removal can crash things, but during normal operation, I just need i/o to always always work. so far, for using ethernet and usb-audio, I have not seen lockups. it streams music over nfs or samba using wired eithernet. for me, its behind powerline ethernet modules (known to be somewhat slow but still reliable) and that lets me put the pi and its dac in another room and still avoid wifi.

I do recommend getting mpd installed. you'll have to read up on what that means, but its usually not much more than 'apt-get install mpd' and a client (its front end) would be 'apt-get install ncmpc' (the client I use the most). there are webserver methods of controlling the music (playlist, shuttle control, etc) and even android/iphone clients to connect to mpd and control it.

I have a fully configured mpd system on sd-card. I would upload it if it was practical, but its an 8gig card (the size I recommend) and even compressed, it will be at least 4gig, I would guess. my upload speed is not really good enough to push up a 4gb file
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Old 11th January 2013, 09:31 AM   #2054
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As linuxworks says, there are no elite hacks required. Just use the latest Raspbian Wheezy image from here. Downloads | Raspberry Pi The audio driver in it supports the USB-I2S in UAC2 mode.

Then install mpd (it's available as a package for Raspbian: so you can just type "sudo apt-get install mpd"- assuming you have your Pi connected to the internet)

Edit the mpd.conf file as shown in the Audio Widget readme, to send output directly to the USB-I2S without resampling. Bingo!

You will need to do a bunch of little tweaks, for instance if you install a USB hard disk, you will need to edit /etc/mtab to get it to mount at boot. I have also had issues with log files filling up the SD card, which I still haven't figured out how to fix.

As far as I know, the "USB elephant" bug has been mitigated a lot by the latest OS releases, but it's not fixed. The problem, as far as I know, is that USB1.1 split transactions are mishandled. Due to excessive interrupt latency in the kernel, the USB stack sometimes misses the deadline for dealing with the second half of the split transaction. This probably causes some sort of error state in the controller that momentarily locks it up, affecting all USB traffic. The underlying issue is that the USB controller hardware doesn't do enough to help the OS, requiring unrealistic interrupt latency. The Broadcom boffins are talking about moving part of the USB stack onto the GPU core to fix this, but I doubt they will get round to it.

I tried lots of things when experimenting with the Tenor chip, including disabling clock management so the CPU runs full speed all the time. I didn't revert these changes this when moving to the USB-I2S, so it may be helping.

I'm considering moving my user interface over to the serial port, so there will be no USB1.1 devices left on the bus.

Once the project is done I will document it fully and maybe BitTorrent an image of the SD card. I wanted to find a way around the "USB elephant" before I went to the effort of building a casing for the system.
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Last edited by scopeboy; 11th January 2013 at 09:41 AM.
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Old 11th January 2013, 09:05 PM   #2055
borges is offline borges  Norway
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I'm finally up and running and able to do serious tests on Linux, PC and Mac! First of all I'm a total Mac newbie. I have a 2010 MacBook with a core 2 duo (I believe).

When the AW is just plugged in and I play music in iTunes, the Mac resamples. In UAC1 it resamples to 48, and in UAC2 it resamples to 192. Is there a way to tell it to not resample?

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Old 11th January 2013, 09:42 PM   #2056
1audio is offline 1audio  United States
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No. That's why Amarra, Pure Music et. al. exist.
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Old 11th January 2013, 09:45 PM   #2057
borges is offline borges  Norway
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Well, I'm a total beginner here. Which player (preferably free of charge) should I download and use on the Mac?

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Old 11th January 2013, 10:48 PM   #2058
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For testing I recommend using iTunes.
With Audio MIDI Setup, you can configure the audio input and output devices. You choose output speed you want to use. Itunes play at that speed.
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Old 12th January 2013, 08:27 AM   #2059
borges is offline borges  Norway
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I have made a new FW release. It's basically a collection of bugfixes for the stable branch. See awx_20130112.zip

This release is very close to the audio-widget stable branch. It uses 16.16 UAC2 feedback, so Windows users must copy the attached .dll file to C:\Program Files (x86)\Audio-Widget (or similar).

The firmware works well on Linux and Windows. On Mac I need to do more testing.

A new debug feature lets you monitor the feedback system.
GPIO_03 = TP51 tracks spk_buf_in
GPIO_04 = TP50 tracks spk_buf_out
Use an oscilloscope and trig on GPIO_04 and see how GPIO_03. Any old 2-channel scope will do!


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Old 12th January 2013, 11:56 AM   #2060
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audirvana is a very convenient player for all audio formats. Exclusive device locking as well as direct connection to the usb layer are possible.
This is the player I would choose for "real listening".
Audirvana | The Sound of Your Dreams
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