USB synchronous control transfers (for usb-to-serial)

[Piet Skiet]

Hi,

Can anyone clarify how to go about doing a synchronous usb control
transfer, similar to Linux's usb_control_msg? I want to implement the
TIOCMGET ioctl on a usb-to-serial converter. The Linux driver uses
synchronous control messages to read DCE and CTS serial pin status,
and I want to do something similar in FreeBSD. The usbdi(9) manpage
talks about control transfers using usbd_transfer_submit, but they're
not synchronous. What about using usbd_transfer_drain? Is there an
example driver showing setting up and doing control transfers?

The ucom driver seems to only implement TIOCSBRK and TIOCCBRK iotcls
at the moment.

Thanks