NAME
ubt —
USB Bluetooth driver
SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file:
device ubtAlternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):
ubt_load="YES"
DESCRIPTION
Theubt driver provides support for USB Bluetooth
dongles to the Bluetooth protocol stack.
USB Bluetooth dongles provide two interfaces, both of which the
ubt 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
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.
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.
- 0
- No active voice channels
- 1
- One voice channel with 8-bit encoding
- 2
- Two voice channels with 8-bit encoding, or one voice channel with 16-bit encoding.
- 3
- Three voice channels with 8-bit encoding
- 4
- Two voice channels with 16-bit encoding
- 5
- Three voice channels with 16-bit encoding
SEE ALSO
HISTORY
This ubt device driver was originally a
character device written by David Sainty and
Lennart Augustsson. It was rewritten to support
socket based Bluetooth access for NetBSD 4.0 by
Iain Hibbert. The ubt driver
was imported into DragonFly 1.11.
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 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 ‘hw.ubtN.sco_txsize’ sysctl variable.
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:
(17 * 1) - 3 = 14(17 * 2) - 3 = 31(17 * 3) - 3 = 48(17 * 4) - 3 = 65(17 * 5) - 3 = 82etc.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.
The SCO packet size can be changed using the ‘scomtu’ option to btconfig(8).
The failure mode is that the USB Bluetooth dongle locks up though generally removal/reinsertion will clear the problem.
BUGS
The Isochronous configuration can only be changed when the device is not marked up.