re: Understanding's snippet of athn(9) code

[matthew green <mrg%eterna.com.au@localhost>]

Farhan Khan writes:
> Hi all,
> I am trying to understand a snippet of athn(9) code for the purpose of
> porting to FreeBSD. I am reading the function athn_usb_htc_setup()
> located in /usr/src/sys/dev/usb/if_athn_usb.c. After tracing it
> through, it seems to terminate at a usbd_setup_xfer(9) call.
>
> Is this the equivalent of setting up which USB function will handle
> which channel? This function seems similar to FreeBSD's
> usbd_transfer_setup(9), which I believe does that. If so, how is that
> different from athn_usb_open_pipes()?
>
> If not, what does athn_usb_htc_setup() do? It is not clear to me and
> therefore I am having trouble making the translation.

usbd_setup_xfer() is used to setup one USB transfer.  it
requires that an open pipe already be provided.  the
"TRANSFERS" section of usbdi.9 in netbsd has more details
than the above:

   https://man.netbsd.org/usbdi.9

it doesn't do much more than fill in the "usbd_xfer"
structure for the transfer operation - does not change
the status of the device in any way until the transfer
is actually submitted.


.mrg.