Copyright (c) 2006 Itronix Inc.
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Written by Iain Hibbert for Itronix Inc.
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.Dd July 26, 2006 .Dt BTSCO 4 .Os .Sh NAME .Nm btsco .Nd Bluetooth SCO Audio .Sh SYNOPSIS .Cd "btsco* at btdev?" .Cd "audio* at audiobus?" .Sh DESCRIPTION The .Nm driver provides support for Bluetooth SCO Audio devices through the .Xr audio 4 driver, and only supports playing and recording of 8kHz, 16-bit, 1 channel, signed linear samples.
p The .Nm driver must be configured at run time with the .Xr btcontrol 8 program. The following properties are used by the .Nm driver during autoconfiguration:
p l -tag -width listenXX t local-bdaddr Local device address. t remote-bdaddr Remote device address. t device-type Should be .Sq btsco , indicating an SCO Audio device. t mtu Packet Size to use, see .Sx CAVEATS section below for details. t listen If this boolean value exists and is true, the .Nm device will, on .Xr open 2 , listen for incoming connections from the remote device. Otherwise, .Nm will attempt to initiate a connection to the remote device. t rfcomm-channel This integer value is not used directly, but will be stored and passed via the .Dv BTSCO_INFO ioctl as below: .El
p SCO connections require a baseband connection between the two devices before they can be created. The .Nm driver does not create this, but can provide information to facilitate an application setting up a control channel prior to use, via the .Dv BTSCO_INFO .Xr ioctl 2 call on the mixer device, which returns a .Ar btsco_info structure as follows: d -literal -offset #include \*[Lt]dev/bluetooth/btsco.h\*[Gt] struct btsco_info { bdaddr_t laddr; /* controller bdaddr */ bdaddr_t raddr; /* headset bdaddr */ uint8_t channel; /* RFCOMM channel */ int vgs; /* mixer index speaker */ int vgm; /* mixer index mic */ }; #define BTSCO_INFO _IOR('b', 16, struct btsco_info) .Ed
p The .Nm driver can be configured to act in Connect or Listen mode. In Connect mode, the .Nm driver will initate a connection to the remote device on an .Xr open 2 call, whereas in Listen mode, .Xr open 2 will block until the remote device initiates the connection. .Sh SEE ALSO .Xr bthset 1 , .Xr ioctl 2 , .Xr audio 4 , .Xr bluetooth 4 , .Xr btdev 4 , .Xr btcontrol 8 .Sh HISTORY The .Nm driver was written for .Nx 4.0 by .An Iain Hibbert under the sponsorship of Itronix, Inc. .Sh CAVEATS Isochronous data is seemingly not well supported over USB in the current system and to get a headset working, you will have to do some research and fine tuning.
p Look at .Xr ubt 4 with regards to the .Xr sysctl 8 settings. Then, you will have to calculate the MTU that the driver will use. This should be less than the sco_mtu reported by the .Xr btconfig 8 program, and when combined with the SCO header (3 bytes) should fit exactly into an integer number of frames, where the frame size is indicated by hw.ubtN.sco_txsize.
p For example: I want one voice channel (which is all that is supported, for now) so am using configuration number 2, with a frame length of 17 bytes. My USB dongle says the maximum SCO payload is 64 bytes, so I am using an MTU of 48 bytes (17 * 3 - 3 = 48).
p Specify the MTU when you configure the SCO audio device with .Xr btcontrol 8 and all should be well.
p The failure mode is that the USB Bluetooth dongle locks up and requires removal/reinsertion to clear.