| ISO(7) | Linux System Administration | ISO(7) |
NAME¶
iso - ISO transport
SYNOPSIS (SINCE LINUX 6.0 [EXPERIMENTAL])¶
#include <sys/socket.h> #include <bluetooth/bluetooth.h> #include <bluetooth/iso.h> iso_socket = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_ISO);
DESCRIPTION¶
Bluetooth Isochronous Channels is a feature introduced in Bluetooth 5.2 that allow for the transmission of multiple, synchronized audio streams between devices.
For unicast/multi-stream audio, connected isochronous group (CIG), and connected isochronous stream (CIS) are used. A CIG is created by the central and it can include one or more CISs. A CIS is a point-to-point data transportation stream between a central and a certain peripheral, and is a bidirectional communication protocol with acknowledgment.
For broadcast audio, broadcast isochronous group (BIG) and broadcast isochronous stream (BIS) are used. There are two types of devices: isochronous broadcaster and synchronized receiver. A BIG is created by an isochronous broadcaster, and it can include one or more BISs. A BIS is a one-to-many data transportation stream.
SOCKET ADDRESS¶
struct sockaddr_iso_bc {
bdaddr_t bc_bdaddr;
uint8_t bc_bdaddr_type;
uint8_t bc_sid;
uint8_t bc_num_bis;
uint8_t bc_bis[ISO_MAX_NUM_BIS];
};
struct sockaddr_iso {
sa_family_t iso_family;
bdaddr_t iso_bdaddr;
uint8_t iso_bdaddr_type;
struct sockaddr_iso_bc iso_bc[];
};
Unicast example:
struct sockaddr_iso addr; memset(&addr, 0, sizeof(addr)); addr.iso_family = AF_BLUETOOTH; bacpy(&addr.iso_bdaddr, bdaddr); addr.iso_bdaddr_type = BDADDR_LE_PUBLIC;
Broadcast example:
struct sockaddr_iso *addr; size_t addr_len; addr_len = sizeof(*addr) + sizeof(*addr->iso_bc); memset(addr, 0, addr_len); addr->iso_family = AF_BLUETOOTH; bacpy(&addr->iso_bdaddr, bdaddr); addr->iso_bdaddr_type = BDADDR_LE_PUBLIC;
Broadcast Source (Broadcaster) example:
struct sockaddr_iso *addr; size_t addr_len; addr_len = sizeof(*addr) + sizeof(*addr->iso_bc); memset(addr, 0, addr_len); addr->iso_family = AF_BLUETOOTH; /* Set address to BDADR_ANY(00:00:00:00:00:00) */ bacpy(&addr->iso_bdaddr, BADDR_ANY); addr->iso_bdaddr_type = BDADDR_LE_PUBLIC; /* Connect to Broadcast address */ connect(iso_socket, (struct sockaddr *)addr, addr_len);
Broadcast Sink (Receiver) example:
struct sockaddr_iso *addr; size_t addr_len; addr_len = sizeof(*addr) + sizeof(*addr->iso_bc); memset(addr, 0, addr_len); addr->iso_family = AF_BLUETOOTH; /* Set destination to Broadcaster address */ bacpy(&addr->iso_bdaddr, bdaddr); addr->iso_bdaddr_type = BDADDR_LE_PUBLIC; /* Bind to Broadcaster address */ bind(iso_socket, (struct sockaddr *)addr, addr_len);
SOCKET OPTIONS (SOL_BLUETOOTH)¶
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¶
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 (since Linux 3.15) | 4 (Secure Only) | Authenticated (P-256 based Secure Simple Pairing and Secure Authentication) | Required |
Example:
int level = BT_SECURITY_HIGH; int err = setsockopt(iso_socket, SOL_BLUETOOTH, BT_SECURITY, &level,
sizeof(level)); if (err == -1) {
perror("setsockopt");
return 1; }
BT_DEFER_SETUP¶
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(iso_socket, SOL_BLUETOOTH, BT_DEFER_SETUP,
&defer_setup, sizeof(defer_setup)); if (err == -1) {
perror("setsockopt");
return err; } err = listen(iso_socket, 5); if (err) {
perror("listen");
return err; } struct sockaddr_iso remote_addr = {0}; socklen_t addr_len = sizeof(remote_addr); int new_socket = accept(iso_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_PKT_STATUS¶
Enable reporting packet status via BT_SCM_PKT_STATUS CMSG on received packets. Possible values:
| Value | Description |
| 0 | Disable (default) |
| 1 | Enable |
- BT_SCM_PKT_STATUS
- Level SOL_BLUETOOTH CMSG with data:
uint8_t pkt_status;
The values are equal to the "Packet_Status_Flag" defined in Core Specification v6.1, 5.4.5. HCI ISO Data packets:
| pkt_status | Description |
| 0x0 | Valid data. The complete SDU was received correctly. |
| 0x1 | Possibly invalid data. The contents of the ISO_SDU_Fragment |
| may contain errors or part of the SDU may be missing. | |
| This is reported as "data with possible errors". | |
| 0x2 | Part(s) of the SDU were not received correctly. |
| This is reported as "lost data". |
SOCKET OPTIONS (SOL_SOCKET)¶
SOL_SOCKET level socket options that modify generic socket features (SO_SNDBUF, SO_RCVBUF, etc.) have their usual meaning, see socket(7).
The SOL_SOCKET level ISO socket options that have Bluetooth-specific handling in kernel are listed below.
SO_TIMESTAMPING, SO_TIMESTAMP, SO_TIMESTAMPNS¶
See <https://docs.kernel.org/networking/timestamping.html>
For ISO sockets, software RX timestamps are supported. Software TX timestamps (SOF_TIMESTAMPING_TX_SOFTWARE) are supported since Linux 6.15.
The software RX timestamp is the time when the kernel received the packet from the controller driver.
The SCM_TSTAMP_SND timestamp is emitted when packet is sent to the controller driver.
The SCM_TSTAMP_COMPLETION timestamp is emitted when controller reports the packet completed. Completion timestamps are only supported on controllers that have ISO flow control. Other TX timestamp types are not supported.
You can use SIOCETHTOOL to query supported flags.
The timestamps are in CLOCK_REALTIME time.
Example (Enable RX timestamping):
int flags = SOF_TIMESTAMPING_SOFTWARE |
SOF_TIMESTAMPING_RX_SOFTWARE; setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &flags, sizeof(flags));
Example (Read packet and its RX timestamp):
char data_buf[256];
union {
char buf[CMSG_SPACE(sizeof(struct scm_timestamping))];
struct cmsghdr align;
} control;
struct iovec data = {
.iov_base = data_buf,
.iov_len = sizeof(data_buf),
};
struct msghdr msg = {
.msg_iov = &data,
.msg_iovlen = 1,
.msg_control = control.buf,
.msg_controllen = sizeof(control.buf),
};
struct scm_timestamping tss;
res = recvmsg(fd, &msg, MSG_ERRQUEUE | MSG_DONTWAIT);
if (res < 0)
goto error;
for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING)
memcpy(&tss, CMSG_DATA(cmsg), sizeof(tss));
}
tstamp_clock_realtime = tss.ts[0];
Example (Enable TX timestamping):
int flags = SOF_TIMESTAMPING_SOFTWARE |
SOF_TIMESTAMPING_TX_SOFTWARE |
SOF_TIMESTAMPING_OPT_ID; setsockopt(fd, SOL_SOCKET, SO_TIMESTAMPING, &flags, sizeof(flags));
Example (Read TX timestamps):
union {
char buf[CMSG_SPACE(sizeof(struct scm_timestamping))];
struct cmsghdr align;
} control;
struct iovec data = {
.iov_base = NULL,
.iov_len = 0
};
struct msghdr msg = {
.msg_iov = &data,
.msg_iovlen = 1,
.msg_control = control.buf,
.msg_controllen = sizeof(control.buf),
};
struct cmsghdr *cmsg;
struct scm_timestamping tss;
struct sock_extended_err serr;
int res;
res = recvmsg(fd, &msg, MSG_ERRQUEUE | MSG_DONTWAIT);
if (res < 0)
goto error;
for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_TIMESTAMPING)
memcpy(&tss, CMSG_DATA(cmsg), sizeof(tss));
else if (cmsg->cmsg_level == SOL_BLUETOOTH && cmsg->cmsg_type == BT_SCM_ERROR)
memcpy(&serr, CMSG_DATA(cmsg), sizeof(serr));
}
tstamp_clock_realtime = tss.ts[0];
tstamp_type = serr->ee_info; /* SCM_TSTAMP_SND or SCM_TSTAMP_COMPLETION */
tstamp_seqnum = serr->ee_data;
IOCTLS¶
The following ioctls with operation specific for ISO sockets are available.
SIOCETHTOOL (since Linux 6.16-rc1)¶
Supports only command ETHTOOL_GET_TS_INFO, which may be used to query supported SOF_TIMESTAMPING_* flags. The SOF_TIMESTAMPING_OPT_* flags are always available as applicable.
Example:
#include <linux/ethtool.h>
#include <linux/sockios.h>
#include <net/if.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
...
struct ifreq ifr = {};
struct ethtool_ts_info cmd = {};
int sk;
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "hci0");
ifr.ifr_data = (void *)&cmd;
cmd.cmd = ETHTOOL_GET_TS_INFO;
sk = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_ISO);
if (sk < 0)
goto error;
if (ioctl(sk, SIOCETHTOOL, &ifr))
goto error;
sof_available = cmd.so_timestamping;
RESOURCES¶
REPORTING BUGS¶
<linux-bluetooth@vger.kernel.org>
SEE ALSO¶
COPYRIGHT¶
Free use of this software is granted under the terms of the GNU Lesser General Public Licenses (LGPL).
| July 2025 | BlueZ |