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
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Architecture | PCI-based systems |
+--------------------+-------------------+
|Interface stability | Committed |
+--------------------+-------------------+
SEE ALSO
attributes(7),
usb_alloc_isoc_req(9F),
usb_get_max_pkts_per_isoc_request(9F),
usb_pipe_get_max_bulk_transfer_size(9F),
usb_pipe_isoc_xfer(9F),
usb_isoc_request(9S) July 25, 2004
USB_GET_CURRENT_FRAME_NUMBER(9F)