Hi folks
I recently got a Line6 Helix LT which can work usb compliant for example on
OSX or IOS. No driver is needed but the samplerate is fixed to 48000 ( which is okay for the first ).
Now i expected this device to work ootb in alsa, which turned out to be half the truth.
Connecting the device threw " usb 7-2: parse_audio_format_rates_v2(): unable to retrieve number of sample rates (clock 16)"
so i investigated a bit and found this workaround:
--- "/media/Workdata3/Development/kernel_lowlat_4.4-97/linux-4.4.97/sound/usb/clock (Kopie).c" 2017-11-08 10:06:31.000000000 +0100 +++ /media/Workdata3/Development/kernel_lowlat_4.4-97/linux-4.4.97/sound/usb/clock.c 2017-11-14 23:06:51.750924051 +0100 @@ -361,6 +361,13 @@ static int set_sample_rate_v2(struct snd struct uac_clock_source_descriptor *cs_desc;
clock = snd_usb_clock_find_source(chip, fmt->clock, true); + /* + * Line6 HELIX does not respond to sample rate + * set requests. The only valid rate is 48000. + */ + if (chip->usb_id == USB_ID(0x0e41, 0x4244) && rate == 48000) + return 0; + if (clock < 0) return clock;
--- "/media/Workdata3/Development/kernel_lowlat_4.4-97/linux-4.4.97/sound/usb/format (Kopie).c" 2017-11-08 10:06:31.000000000 +0100 +++ /media/Workdata3/Development/kernel_lowlat_4.4-97/linux-4.4.97/sound/usb/format.c 2017-11-14 23:12:24.329766243 +0100 @@ -293,6 +293,20 @@ static int parse_audio_format_rates_v2(s int nr_triplets, data_size, ret = 0; int clock = snd_usb_clock_find_source(chip, fp->clock, false);
+ /* + * Line6 HELIX does not respond to sample rate + * query requests. The only valid rate is 48000. + */ + if (chip->usb_id == USB_ID(0x0e41, 0x4244)) { + fp->nr_rates = 1; + fp->rate_min = 48000; + fp->rate_max = 48000; + fp->rates = SNDRV_PCM_RATE_48000; + fp->rate_table = kmalloc(sizeof(int), GFP_KERNEL); + fp->rate_table[0] = 48000; + return 0; + } + if (clock < 0) { dev_err(&dev->dev, "%s(): unable to find clock source (clock %d)\n",
This trick made the device appear in aplay -l and /proc/asound just as expected.
[ 7988.495085] usb 7-2: new high-speed USB device number 4 using xhci_hcd [ 7988.663622] usb 7-2: New USB device found, idVendor=0e41, idProduct=4244 [ 7988.663625] usb 7-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 7988.663627] usb 7-2: Product: HELIX [ 7988.663629] usb 7-2: Manufacturer: LINE 6 [ 7988.663630] usb 7-2: SerialNumber: 2744535
But i ended up with sometimes occuring soft clicks in playback which imply i have timing problems.
Another symptom is aplay does not output any sound while not throwing any error while in jack i can create the driver just fine.
I would apreciate any hint what i could try out here.
Greetings from Hamburg ... Jens