illumos: manual page: usb_get_current_frame

USB_GET_CURRENT_FRAME_NUMBER(9F) Kernel Functions for Drivers

NAME

usb_get_current_frame_number - Return current logical usb frame number

SYNOPSIS

#include <sys/usb/usba.h>

usb_frame_number_t usb_get_current_frame_number(dev_info_t *dip);

INTERFACE LEVEL

illumos DDI specific (illumos DDI)

PARAMETERS

dip
Pointer to the device's dev_info structure.

DESCRIPTION

The usb_get_current_frame_number() function retrieves the current logical
USB frame number.

Isochronous requests can be started on a particular numbered frame. An
offset number of frames (typically between 4 and 10) can be added to the
current logical frame number to specify the number of an upcoming frame
to start an isochronous request.

The USB specification requires that the frame frequency (the period
between start-of-frame packets) is one millisecond. The illumos
operating environment USB implementation uses a running counter of the
number of milliseconds since boot as the current logical frame number.

RETURN VALUES

On success, the usb_get_current_frame_number() function returns the
current USB frame number. On failure it returns 0. The function fails if
dip is NULL.

CONTEXT

May be called from user, kernel or interrupt context.

EXAMPLES

usb_pipe_handle_t handle;
usb_frame_number_t offset = 10;
usb_isoc_req_t *isoc_req;

isoc_req = usb_alloc_isoc_req(...);
...
...
isoc_req->isoc_frame_no = usb_get_current_frame_number(dip) + offset;
isoc_req->isoc_attributes = USB_ATTRS_ISOC_START_FRAME;
...
...
if (usb_pipe_isoc_xfer(handle, isoc_req, 0) != USB_SUCCESS) {
...
}

ATTRIBUTES