.\" $NetBSD: ubt.4,v 1.6 2006/09/10 20:09:11 plunky Exp $
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.Dd August 27, 2006
.Dt UBT 4
.Os
.Sh NAME
.Nm ubt
.Nd USB Bluetooth driver
.Sh SYNOPSIS
.Cd "ubt* at uhub? port ? configuration ? interface ?"
.Sh DESCRIPTION
The
.Nm
driver provides support for USB Bluetooth dongles
to the Bluetooth protocol stack.
.Pp
USB Bluetooth dongles provide two interfaces, both of which the
.Nm
driver claims.
The second interface is used for Isochronous data and will have
several alternate configurations regarding bandwidth consumption,
which can be set using the hw.ubtN.config
.Xr sysctl 8
variable.
The number of alternate configurations is indicated by the value
in the hw.ubtN.alt_config variable, and the isoc frame size for the current
configuration is shown in the hw.ubtN.sco_rxsize and hw.ubtN.sco_txsize
variables.
.Pp
By default, configuration 0 is selected, which means that no bandwidth
is used on the Isochronous interface and no SCO data can be sent.
Consult the Bluetooth USB specification at https://www.bluetooth.org/
for complete instructions on setting bandwidth consumption.
The following extract may be
useful as a general guidance though details may differ between manufacturers.
.Pp
.Bl -tag -compact -width XXX
.It 0
No active voice channels
.It 1
One voice channel with 8-bit encoding
.It 2
Two voice channels with 8-bit encoding, or one voice channel with
16-bit encoding.
.It 3
Three voice channels with 8-bit encoding
.It 4
Two voice channels with 16-bit encoding
.It 5
Three voice channels with 16-bit encoding
.El
.Sh SEE ALSO
.Xr bluetooth 4 ,
.Xr uhub 4 ,
.Xr sysctl 8
.Sh HISTORY
This
.Nm
device driver was originally a character device written by
.An David Sainty
and
.An Lennart Augustsson .
It was rewritten to support socket based Bluetooth access for
.Nx 4.0
by
.An Iain Hibbert .
.Sh CAVEATS
Isochronous data is seemingly not well supported over USB in the current
system and to get SCO working, you may have to calculate the SCO packet
size that the stack will use.
This is the sco_mtu value reported by the
.Xr btconfig 8
command, and when combined with the SCO header (3 bytes) should
fit exactly into an integer number of Isochronous data frames where
the frame size is indicated by the
.Sq hw.ubtN.sco_txsize
sysctl variable.
.Pp
For example: I want one voice channel (which is all that is supported,
for now) so am using configuration #2, with a frame length of 17
bytes.
This gives possible values of:
.Pp
.Dl "(17 * 1) - 3 = 14"
.Dl "(17 * 2) - 3 = 31"
.Dl "(17 * 3) - 3 = 48"
.Dl "(17 * 4) - 3 = 65"
.Dl "(17 * 5) - 3 = 82"
.Dl "etc."
.Pp
.Xr btconfig 8
shows the maximum SCO payload as 64 bytes, so I am using the next smaller
size of 48, to minimize the overhead of the 3 header bytes.
.Pp
The SCO packet size can be changed using the
.Sq scomtu
option to
.Xr btconfig 8 .
.Pp
The failure mode is that the USB Bluetooth dongle locks up though
generally removal/reinsertion will clear the problem.
.Sh BUGS
The Isochronous configuration can only be changed when the device is not
marked up.