drmatt wrote: 
> Based on what OS, kernel, and software stack?
> 
> The udev system should handle initialisation of the DAC if it's plugged
> in post boot. You should at least see a kernel log message when the DAC
> joins the USB bus, even if no driver subsequently loads to manage it.

Armbian os (xenial) with logsleep (allwinner) kernel 3.10.104 (the only
viable kernel for the pine64 soc device at the moment).

Having posted, I can't reproduce the second scenario now, so please
forget that for the moment.

The white noise is still present though, as soon as alsa loads.

Stack would probably be something like:

1. ehci:

Code:
--------------------
    dmesg:
  [ 3092.731854] ehci_irq: highspeed device connect
  [ 3092.953708] usb 2-1: new high-speed USB device number 2 using sunxi-ehci
  [ 3093.181941] usbcore: registered new interface driver usbhid
  [ 3093.181952] usbhid: USB HID core driver
  [ 3094.710561] input: SMSL AUDIO Sanskrit PRO as 
/devices/soc.0/1c1b000.ehci1-controller/usb2/2-1/2-1:1.2/input/input6
  [ 3094.712441] hid-generic 0003:0D8C:0062.0001: input,hidraw0: USB HID v1.00 
Device [SMSL AUDIO Sanskrit PRO] on usb-sunxi-ehci-1/input2
--------------------


2. ALSA:

Code:
--------------------
    aplay -L
  null
  Discard all samples (playback) or generate zero samples (capture)
  pulse
  PulseAudio Sound Server
  default:CARD=PRO
  Sanskrit PRO, USB Audio
  Default Audio Device
  sysdefault:CARD=PRO
  Sanskrit PRO, USB Audio
  Default Audio Device
  front:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  Front speakers
  surround21:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  2.1 Surround output to Front and Subwoofer speakers
  surround40:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  4.0 Surround output to Front and Rear speakers
  surround41:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  4.1 Surround output to Front, Rear and Subwoofer speakers
  surround50:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  5.0 Surround output to Front, Center and Rear speakers
  surround51:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  5.1 Surround output to Front, Center, Rear and Subwoofer speakers
  surround71:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
  iec958:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  IEC958 (S/PDIF) Digital Audio Output
  dmix:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  Direct sample mixing device
  dsnoop:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  Direct sample snooping device
  hw:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  Direct hardware device without any conversions
  plughw:CARD=PRO,DEV=0
  Sanskrit PRO, USB Audio
  Hardware device with all software conversions
--------------------


squeezelite:

Code:
--------------------
    squeezelite-R2 -l
  Output devices:
  null                           - Discard all samples (playback) or generate 
zero samples (capture)
  pulse                          - PulseAudio Sound Server
  default                       
  sysdefault:CARD=PRO            - Sanskrit PRO, USB Audio - Default Audio 
Device
  front:CARD=PRO,DEV=0           - Sanskrit PRO, USB Audio - Front speakers
  surround21:CARD=PRO,DEV=0      - Sanskrit PRO, USB Audio - 2.1 Surround 
output to Front and Subwoofer speakers
  surround40:CARD=PRO,DEV=0      - Sanskrit PRO, USB Audio - 4.0 Surround 
output to Front and Rear speakers
  surround41:CARD=PRO,DEV=0      - Sanskrit PRO, USB Audio - 4.1 Surround 
output to Front, Rear and Subwoofer speakers
  surround50:CARD=PRO,DEV=0      - Sanskrit PRO, USB Audio - 5.0 Surround 
output to Front, Center and Rear speakers
  surround51:CARD=PRO,DEV=0      - Sanskrit PRO, USB Audio - 5.1 Surround 
output to Front, Center, Rear and Subwoofer speakers
  surround71:CARD=PRO,DEV=0      - Sanskrit PRO, USB Audio - 7.1 Surround 
output to Front, Center, Side, Rear and Woofer speakers
  iec958:CARD=PRO,DEV=0          - Sanskrit PRO, USB Audio - IEC958 (S/PDIF) 
Digital Audio Output
  dmix:CARD=PRO,DEV=0            - Sanskrit PRO, USB Audio - Direct sample 
mixing device
  dsnoop:CARD=PRO,DEV=0          - Sanskrit PRO, USB Audio - Direct sample 
snooping device
  hw:CARD=PRO,DEV=0              - Sanskrit PRO, USB Audio - Direct hardware 
device without any conversions
  plughw:CARD=PRO,DEV=0          - Sanskrit PRO, USB Audio - Hardware device 
with all software conversions
--------------------


The default output device for squeezelite is
hw:CARD=PRO,DEV=0              - Sanskrit PRO, USB Audio - Direct
hardware device without any conversions

which obviously causes squeezelite startup to fail when the card is not
found.

I'm thinking that I should modify the startup script for squeezelite to
wait until the  hw:CARD=PRO,DEV=0 is present, before starting. Should be
a way of doing that, or taking the squeezelite start script out of init
and link it to a udev rule ???

But I'm sure that I'm not the first to have the problem, so there's
probably a standard solution lying around somewhere, if I can find it.

Regarding the white noise, I'm guessing that alsa is initialising the
device in the wrong mode somehow. Again: any standard solution that may
be missing on my system??

BR.


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