[LAD] [sound/usb/line6] Question on PODHD Edit features like implementation

Nicolas SCHWARTZ Aurryon social at staraurryon.com
Tue Jul 14 23:10:43 CEST 2020

Dear Linux Audio Dev Team,

I am looking to re implement and publish with the help of Wireshark a
software like Line6 PODHD 500x Edit for my POD HD500X (modification of
guitar pedal effects). To do this I need to claim the usb interface that
is already used by the snd-usb-podhd and redo the initialisation, also
already done by snd-usb-podhd. Therefore, to have both the audio and the
pedal management I would need to modify the module mentioned above. This
would aim to create a bridge between kernel and the userspace, that
redirects the usb urb bulk requests that are not used by the audio part,
to an interface (only isochronous is used after the init).

In the objective to be merged upstream in the future, how should I proceed:

  * Use midi interfaces and create a fake one, knowing that the
    proprietary but readable protocol is not midi compliant?
  * Create a char device for the podhd pedal boards? Within the same module?
  * Other suggestions?

In the same way, I am looking for suggestion regarding the data
transmitted within this interface. Would something like struct {int
message_len, char * data} be sufficient to be transmitted at every urb
bulk request?

Thanks in advance,


PS: I can share with you my test code and my current analysis on the
messages sent/received by the pod when clicking on buttons/sending
message from the PC, if needed.

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