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CONFIG_BT_BUF_ACL_TX_SIZE

Maximum supported ACL size for outgoing data

Type: int

Help

Maximum supported ACL size of data packets sent from the Host to the
Controller. This value does not include the HCI ACL header.
The Host will segment the data transmitted to the Controller so that
packets sent to the Controller will contain data up to this size.
In a combined build this value will be set in both the Host and the
Controller.
In a Host-only build the Host will read the maximum ACL size supported
by the Controller and use the smallest value supported by both the
Bost and the Controller.
The Host supports sending of larger L2CAP PDUs than the ACL size and
will fragment L2CAP PDUs into ACL data packets.
The Controller will return this value in the HCI LE Read Buffer
Size command response. If this size if greater than effective Link
Layer transmission size then the Controller will perform
fragmentation before transmitting the packet(s) on air.
If this value is less than the effective Link Layer transmission size
then this will restrict the maximum Link Layer transmission size.
Maximum is set to 251 due to implementation limitations (use of
uint8_t for length field in PDU buffer structure).

Direct dependencies

BT_HCI && BT

(Includes any dependencies from ifs and menus.)

Default

  • 27

Kconfig definition

At subsys/bluetooth/common/Kconfig:7

Included via Kconfig:8Kconfig.zephyr:42subsys/Kconfig:9subsys/bluetooth/Kconfig:322

Menu path: (Top) → Sub Systems and OS Services → Bluetooth

config BT_BUF_ACL_TX_SIZE
    int "Maximum supported ACL size for outgoing data"
    range 27 251
    default 27
    depends on BT_HCI && BT
    help
      Maximum supported ACL size of data packets sent from the Host to the
      Controller. This value does not include the HCI ACL header.
      The Host will segment the data transmitted to the Controller so that
      packets sent to the Controller will contain data up to this size.
      In a combined build this value will be set in both the Host and the
      Controller.
      In a Host-only build the Host will read the maximum ACL size supported
      by the Controller and use the smallest value supported by both the
      Bost and the Controller.
      The Host supports sending of larger L2CAP PDUs than the ACL size and
      will fragment L2CAP PDUs into ACL data packets.
      The Controller will return this value in the HCI LE Read Buffer
      Size command response. If this size if greater than effective Link
      Layer transmission size then the Controller will perform
      fragmentation before transmitting the packet(s) on air.
      If this value is less than the effective Link Layer transmission size
      then this will restrict the maximum Link Layer transmission size.
      Maximum is set to 251 due to implementation limitations (use of
      uint8_t for length field in PDU buffer structure).

(The ‘depends on’ condition includes propagated dependencies from ifs and menus.)