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sco - SCO transport
Contents
Copyright
Free use of this software is granted under the terms of the GNU Lesser General Public Licenses (LGPL).
BlueZ March 2025 SCO(7)
Description
The SCO logical transport, is a symmetric, point-to-point transport between the Central and a specific
Peripheral. The SCO logical transport reserves slots and can therefore be considered as a
circuit-switched connection between the Central and the Peripheral.
In addition to the reserved slots, when eSCO is supported, a retransmission window follows immediately
after. Together, the reserved slots and the retransmission window form the complete eSCO window.
Name
sco - SCO transport
Reporting Bugs
Resources
See Also
socket(7), scotest(1)
Socket Address
struct sockaddr_sco {
sa_family_t sco_family;
bdaddr_t sco_bdaddr;
};
Example:
struct sockaddr_sco addr;
memset(&addr, 0, sizeof(addr));
addr.sco_family = AF_BLUETOOTH;
bacpy(&addr.sco_bdaddr, bdaddr);
Socket Options
The socket options listed below can be set by using setsockopt(2) and read with getsockopt(2) with the
socket level set to SOL_BLUETOOTH.
BT_SECURITY(sinceLinux2.6.30)
Channel security level, possible values:
┌────────────────────┬──────────────────────┬────────────────────────┬──────────────┐
│ Value │ Security Level │ Link Key Type │ Encryption │
├────────────────────┼──────────────────────┼────────────────────────┼──────────────┤
│ BT_SECURITY_SDP │ 0 (SDP Only) │ None │ Not required │
├────────────────────┼──────────────────────┼────────────────────────┼──────────────┤
│ BT_SECURITY_LOW │ 1 (Low) │ Unauthenticated │ Not required │
├────────────────────┼──────────────────────┼────────────────────────┼──────────────┤
│ BT_SECURITY_MEDIUM │ 2 (Medium - default) │ Unauthenticated │ Desired │
├────────────────────┼──────────────────────┼────────────────────────┼──────────────┤
│ BT_SECURITY_HIGH │ 3 (High) │ Authenticated │ Required │
├────────────────────┼──────────────────────┼────────────────────────┼──────────────┤
│ BT_SECURITY_FIPS │ 4 (Secure Only) │ Authenticated (P-256 │ Required │
│ (since Linux 3.15) │ │ based Secure Simple │ │
│ │ │ Pairing and Secure │ │
│ │ │ Authentication) │ │
└────────────────────┴──────────────────────┴────────────────────────┴──────────────┘
Example:
int level = BT_SECURITY_HIGH;
int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_SECURITY, &level,
sizeof(level));
if (err == -1) {
perror("setsockopt");
return 1;
}
BT_DEFER_SETUP(sinceLinux2.6.30)
Channel defer connection setup, this control if the connection procedure needs to be authorized by
userspace before responding which allows authorization at profile level, possible values:
┌───────┬───────────────────┬───────────────┐
│ Value │ Description │ Authorization │
├───────┼───────────────────┼───────────────┤
│ 0 │ Disable (default) │ Not required │
├───────┼───────────────────┼───────────────┤
│ 1 │ Enable │ Required │
└───────┴───────────────────┴───────────────┘
Example:
int defer_setup = 1;
int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_DEFER_SETUP,
&defer_setup, sizeof(defer_setup));
if (err == -1) {
perror("setsockopt");
return err;
}
err = listen(sco_socket, 5);
if (err) {
perror("listen");
return err;
}
struct sockaddr_sco remote_addr = {0};
socklen_t addr_len = sizeof(remote_addr);
int new_socket = accept(sco_socket, (struct sockaddr*)&remote_addr,
&addr_len);
if (new_socket < 0) {
perror("accept");
return new_socket;
}
/* To complete the connection setup of new_socket read 1 byte */
char c;
struct pollfd pfd;
memset(&pfd, 0, sizeof(pfd));
pfd.fd = new_socket;
pfd.events = POLLOUT;
err = poll(&pfd, 1, 0);
if (err) {
perror("poll");
return err;
}
if (!(pfd.revents & POLLOUT)) {
err = read(sk, &c, 1);
if (err < 0) {
perror("read");
return err;
}
}
BT_VOICE(sinceLinux3.11)
Transport voice settings, possible values:
struct bt_voice {
uint16_t setting;
};
┌────────────────────────────┬────────┬──────────────────────────────┐
│ Define │ Value │ Description │
├────────────────────────────┼────────┼──────────────────────────────┤
│ BT_VOICE_TRANSPARENT │ 0x0003 │ Transparent output │
├────────────────────────────┼────────┼──────────────────────────────┤
│ BT_VOICE_CVSD_16BIT │ 0x0060 │ C-VSD output PCM 16-bit │
│ │ │ input │
├────────────────────────────┼────────┼──────────────────────────────┤
│ BT_VOICE_TRANSPARENT_16BIT │ 0x0063 │ Transparent output PCM │
│ │ │ 16-bit input │
└────────────────────────────┴────────┴──────────────────────────────┘
Example:
struct bt_voice voice;
memset(&voice, 0, sizeof(voice));
voice.setting = BT_VOICE_TRANSPARENT;
int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_VOICE, &voice,
sizeof(voice));
if (err == -1) {
perror("setsockopt");
return 1;
}
BT_PHY(sinceLinux5.10)
Transport supported PHY(s), possible values:
┌────────────────────┬───────┬─────────────────┐
│ Define │ Value │ Description │
├────────────────────┼───────┼─────────────────┤
│ BT_PHY_BR_1M_1SLOT │ BIT 0 │ BR 1Mbps 1SLOT │
├────────────────────┼───────┼─────────────────┤
│ BT_PHY_BR_1M_3SLOT │ BIT 1 │ BR 1Mbps 3SLOT │
├────────────────────┼───────┼─────────────────┤
│ BT_PHY_BR_2M_1SLOT │ BIT 3 │ EDR 2Mbps 1SLOT │
├────────────────────┼───────┼─────────────────┤
│ BT_PHY_BR_2M_3SLOT │ BIT 4 │ EDR 2Mbps 3SLOT │
├────────────────────┼───────┼─────────────────┤
│ BT_PHY_BR_3M_1SLOT │ BIT 6 │ EDR 3Mbps 1SLOT │
├────────────────────┼───────┼─────────────────┤
│ BT_PHY_BR_3M_3SLOT │ BIT 7 │ EDR 3Mbps 3SLOT │
└────────────────────┴───────┴─────────────────┘
BT_CODEC(sinceLinux5.14)
Transport codec offload, possible values:
struct bt_codec {
uint8_t id;
uint16_t cid;
uint16_t vid;
uint8_t data_path_id;
uint8_t num_caps;
struct codec_caps {
uint8_t len;
uint8_t data[];
} caps[];
} __attribute__((packed));
struct bt_codecs {
uint8_t num_codecs;
struct bt_codec codecs[];
} __attribute__((packed));
Example:
char buffer[sizeof(struct bt_codecs) + sizeof(struct bt_codec)];
struct bt_codec *codecs = (void *)buffer;
memset(codecs, 0, sizeof(codecs));
codec->num_codecs = 1;
codecs->codecs[0].id = 0x05;
codecs->codecs[0].data_path_id = 1;
int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_CODEC, codecs,
sizeof(buffer));
if (err == -1) {
perror("setsockopt");
return 1;
}
Synopsis
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/sco.h>
sco_socket = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_SCO);
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