CC256x versus HCI Commands

1 Introduction

Bluetooth® systems consists of a host and a controller. The BT SIG has created a standard protocol for the host to communicate with the controller. This is called the Host Controller Interface (HCI) which is specified in the BT Core 4.1 specification Volume 2 Part E. The HCI provides a uniform command interface to a Controller. There are some commands which are not listed in the specifications and they are specific to the device itself. These commands are vendor-specific commands (VS) generally used for testing and debugging purposes. For further details on testing command sequences, refer to CC256x Testing Guide.

Figure 1-1 HCI Commands VS

As shown in the diagram above, the host (MSP430) sends HCI commands to the controller (CC256x). The controller then sends HCI events to the host as a response to the HCI commands. All HCI commands follows this format for all packets:

Table 1-1 HCI Packet Format

First Byte	Next Bytes
HCI Packet Type	HCI packet (variable length)

All HCI commands starts with a byte describing type of packet while the remaining bytes is dependent on the type of HCI packet.

Here is a list of important HCI packet types:

Table 1-2 HCI Packet Types

HCI Packet Type	Packet Type Indicator	Direction
HCI command packet	0x01	Host to baseband controller
HCI event packet	0x04	Baseband controller to host

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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.