[alsa-devel] Line6 Helix - usb compliant but not working correct

[Jens Verwiebe]

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

-- 

Jens Verwiebe
Allerskehre 44 - 22309 Hamburg

Tel.: +49 40 68 78 50
mobile: +49 172 400 49 07
mailto: info at jensverwiebe.de
web: http://www.jensverwiebe.de