SWRA751 September 2022

1 Command Packet

Most of the HCI packets consist of command packets. The host sends these command packets according to the structure detailed in the tables below and the controller sends responses through event packets back to the host. Command packets are used to configure many aspects of the Bluetooth system ranging from the link layer to the baseband layer.

You can also refer to the Core 4.1 Specification Volume 2, Part E, for the format of these HCI packets.

After the first byte,the remaining bytes depends on what type of packet it is. Of these two packet types, the structure of the HCI command packet is:

Table 1-1 Command Packet

First Last
16 bit Opcode	8 bit Length	Parameters(0,1,3,...,N)

First

Last

16 bit Opcode

8 bit Length

Parameters(0,1,3,...,N)

Note: Some commands do not have parameters, thus ends with 0x00 as the length.

Here is a description of the above HCI command packet structure:

Table 1-2 HCI Command Description

Fields	Descriptions
Opcode	16 bit unique Opcode for HCI command
Length	Length of parameters in bytes
Parameters	Specific parameters associated with each command

Taking the command HCI_Read_BD_ADDR, this is an example of a command packet consisting of outgoing data to the controller:

Table 1-3 Command Packet Example

Packet Type	Opcode	Opcode	Length
0x01	0x09	0x10	0x00

In this case, the length is zero so no parameters follows afterwards.