alsa-project/alsa-python issue #13 was opened from tormodvolden:
It seems like the "status" member returned by `snd_ctl_elem_value_get_iec958(self->value, iec958);` on pyalsa/alsahcontrol.c line 1053 starts with 0xff then a 0x00.
I haven't been able to find a corresponding node under /proc/asound to check this.
The relevant aplay -L entry is
```
iec958:CARD=Stereo,DEV=0
Logitech H570e Stereo, USB Audio
IEC958 (S/PDIF) Digital Audio Output
```
Here is a dump of /proc/asound/card1 (card 1 is called "Stereo")
<details>
```
$ more $(find /proc/asound/card1 -type f)
::::::::::::::
/proc/asound/card1/id
::::::::::::::
Stereo
::::::::::::::
/proc/asound/card1/pcm0c/info
::::::::::::::
card: 1
device: 0
subdevice: 0
stream: CAPTURE
id: USB Audio
name: USB Audio
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 1
subdevices_avail: 1
::::::::::::::
/proc/asound/card1/pcm0c/sub0/info
::::::::::::::
card: 1
device: 0
subdevice: 0
stream: CAPTURE
id: USB Audio
name: USB Audio
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 1
subdevices_avail: 1
::::::::::::::
/proc/asound/card1/pcm0c/sub0/status
::::::::::::::
closed
::::::::::::::
/proc/asound/card1/pcm0c/sub0/hw_params
::::::::::::::
closed
::::::::::::::
/proc/asound/card1/pcm0c/sub0/sw_params
::::::::::::::
closed
::::::::::::::
/proc/asound/card1/pcm0p/info
::::::::::::::
card: 1
device: 0
subdevice: 0
stream: PLAYBACK
id: USB Audio
name: USB Audio
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 1
subdevices_avail: 0
::::::::::::::
/proc/asound/card1/pcm0p/sub0/info
::::::::::::::
card: 1
device: 0
subdevice: 0
stream: PLAYBACK
id: USB Audio
name: USB Audio
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 1
subdevices_avail: 0
::::::::::::::
/proc/asound/card1/pcm0p/sub0/status
::::::::::::::
state: RUNNING
owner_pid : 1928
trigger_time: 270044.979966617
tstamp : 309371.219688371
delay : 1872
avail : 31520
avail_max : 32032
-----
hw_ptr : 1887652896
appl_ptr : 1887654144
::::::::::::::
/proc/asound/card1/pcm0p/sub0/hw_params
::::::::::::::
access: MMAP_INTERLEAVED
format: S16_LE
subformat: STD
channels: 2
rate: 48000 (48000/1)
period_size: 256
buffer_size: 32768
::::::::::::::
/proc/asound/card1/pcm0p/sub0/sw_params
::::::::::::::
tstamp_mode: ENABLE
period_step: 1
avail_min: 256
start_threshold: 9223372036854775807
stop_threshold: 32768
silence_threshold: 0
silence_size: 0
boundary: 4611686018427387904
::::::::::::::
/proc/asound/card1/usbid
::::::::::::::
046d:0a56
::::::::::::::
/proc/asound/card1/usbbus
::::::::::::::
003/006
::::::::::::::
/proc/asound/card1/stream0
::::::::::::::
Logitech Inc Logitech H570e Stereo at usb-0000:00:14.0-4.4.2, full speed : USB A
udio
Playback:
Status: Running
Interface = 2
Altset = 1
Packet Size = 192
Momentary freq = 48000 Hz (0x30.0000)
Interface 2
Altset 1
Format: S16_LE
Channels: 2
Endpoint: 0x01 (1 OUT) (ADAPTIVE)
Rates: 8000, 16000, 24000, 32000, 44100, 48000
Bits: 16
Channel map: FL FR
Capture:
Status: Stop
Interface 1
Altset 1
Format: S16_LE
Channels: 2
Endpoint: 0x81 (1 IN) (ASYNC)
Rates: 8000, 16000, 24000, 32000, 44100, 48000
Bits: 16
Channel map: FL FR
::::::::::::::
/proc/asound/card1/usbmixer
::::::::::::::
USB Mixer: usb_id=0x046d0a56, ctrlif=0, ctlerr=0
Card: Logitech Inc Logitech H570e Stereo at usb-0000:00:14.0-4.4.2, full speed
Unit: 2
Control: name="Auto Gain Control", index=0
Info: id=2, control=7, cmask=0x0, channels=1, type="BOOLEAN"
Volume: min=0, max=1, dBmin=0, dBmax=0
Unit: 2
Control: name="Headset Capture Volume", index=0
Info: id=2, control=2, cmask=0x0, channels=1, type="S16"
Volume: min=-7680, max=1280, dBmin=-3000, dBmax=500
Unit: 2
Control: name="Headset Capture Switch", index=0
Info: id=2, control=1, cmask=0x0, channels=1, type="INV_BOOLEAN"
Volume: min=0, max=1, dBmin=0, dBmax=0
Unit: 5
Control: name="Headset Playback Volume", index=0
Info: id=5, control=2, cmask=0x3, channels=2, type="S16"
Volume: min=-15360, max=1280, dBmin=-6000, dBmax=500
Unit: 5
Control: name="Headset Playback Switch", index=0
Info: id=5, control=1, cmask=0x0, channels=1, type="INV_BOOLEAN"
Volume: min=0, max=1, dBmin=0, dBmax=0
Unit: 11
Control: name="Sidetone Playback Volume", index=0
Info: id=11, control=2, cmask=0x0, channels=1, type="S16"
Volume: min=0, max=4125, dBmin=0, dBmax=1611
Unit: 11
Control: name="Sidetone Playback Switch", index=0
Info: id=11, control=1, cmask=0x0, channels=1, type="INV_BOOLEAN"
Volume: min=0, max=1, dBmin=0, dBmax=0
```
</details>
This is the last part of the output from running `python3 test/hctltest1.py
`
```
*****
count: 1
device: 0
dimensions: None
element: <alsahcontrol.Element object at 0x7e418ebb9650>
id: (19, 2, 0, 0, 'IEC958 Playback Con Mask', 0)
index: 0
interface: 2
is_inactive: False
is_locked: False
is_owner: False
is_readable: True
is_tlv_Commandable: False
is_tlv_Writable: False
is_tlv_readable: False
is_user: False
is_volatile: False
is_writable: False
name: IEC958 Playback Con Mask
numid: 19
owner: -1
subdevice: 0
type: 5 (IEC958)
-----
device: 0
element: <alsahcontrol.Element object at 0x7e418ebb9650>
get_array: <built-in method get_array of alsahcontrol.Value object at 0x7e418ebb9620>
get_tuple: <built-in method get_tuple of alsahcontrol.Value object at 0x7e418ebb9620>
id: (19, 2, 0, 0, 'IEC958 Playback Con Mask', 0)
index: 0
interface: 2
name: IEC958 Playback Con Mask
numid: 19
read: <built-in method read of alsahcontrol.Value object at 0x7e418ebb9620>
set_array: <built-in method set_array of alsahcontrol.Value object at 0x7e418ebb9620>
set_tuple: <built-in method set_tuple of alsahcontrol.Value object at 0x7e418ebb9620>
subdevice: 0
write: <built-in method write of alsahcontrol.Value object at 0x7e418ebb9620>
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 1: invalid start byte
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/tormod/SOURCES/pyalsa-debian/python-pyalsa/test/hctltest1.py", line 69, in <module>
value(element1)
File "/home/tormod/SOURCES/pyalsa-debian/python-pyalsa/test/hctltest1.py", line 36, in value
values = value.get_tuple(info.type, info.count)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SystemError: <method 'get_tuple' of 'alsahcontrol.Value' objects> returned a result with an exception set
```
info.type is 5 info.count is 1
Issue URL : https://github.com/alsa-project/alsa-python/issues/13
Repository URL: https://github.com/alsa-project/alsa-python
