[Bluetooth Bluetooth development] VIII. Transmission layer of ble protocol

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8.1 Preface

Link Layer The transport layer goes up , It's the transport layer . Transport layer , be located Host and Controller Between layers , Provide the ability to transmit data without knowing the detailed data content . It is mainly transmitted through hardware media （ Such as ：UART、USB、SDIO etc. ）, transmission Bluetooth HCI The data of .

Here is UART Block diagram of the transport layer ：

Look at the picture above , We probably have a general understanding of the transport layer , Let's analyze it in detail .

HCI Detailed introduction , having evidence or referent sources Core5.0 P670

 

8.2 HCI（Host Controller Interface） Introduce

Upper figure , Shows the data transmission path between the two devices .Host adopt HCI Driver Driver and Controller On hardware HCI Firmware Exchange data and commands , The transport layer provides such capabilities .

The main role of the transport layer ：

• The Bluetooth protocol stack sends the connected to the chip command
• Bluetooth chip reports to Bluetooth protocol stack command status with create connection opcode
• Bluetooth chip reports Bluetooth protocol stack connect complete

HCI Provides a unified interface for accessing , control Controller, The transport layer is transparent , Independent of the underlying transmission technology , And no relationship Host Transferred to the Controller What is the data of .

stay HOST And Controller Between , With Command And Event Command mode for transmission .Host send out Command Information to Controller,Controller take Command Status and Params With Event Returned to Host, Finally back to Command Complete Event Indicates that the connection is complete .

More intuitive , as follows ：

HCI There are four types of package formats , Namely ：

• HCI Command Packet： The command sent to the chip by the Bluetooth protocol stack , namely Host -> Controller
• HCI Event Packet： Events reported by Bluetooth chip to Bluetooth protocol stack , namely Controller -> Host
• HCI ACL Data Packet： Common data of two-way interaction between Bluetooth protocol stack and Bluetooth chip .
• HCI Synchronous Data Packet： Common data of two-way interaction between Bluetooth protocol stack and Bluetooth chip .

Detailed see Core5.0.pdf P670

stay Host and Controller Between ,HCI The command and event types of are as follows ：

Detailed see Core5.0.pdf P647

The interactive data format is ：

 

8.3 HCI Packet format

HCI Provides a unified command format to access Controller, Different commands also take different time . The transport layer commands Command And events Event To communicate , Now let's mainly look at the format of communication packets .

 

8.3.1 Handles

Handle： Identification of the channel of the logical link , There are three categories ：Connection_Handles, Logical Link Handles, and Physical Link Handles

8.3.1.1 Primary Controller Handles

Connection_Handles： By Primary Controller Handles Distribute , Identify the logical channel between the host and the master controller , When a new logical link is established ,Connection_Handles Will be assigned .

The Handle It is mainly used in ：Connection Complete, Synchronous Connection Complete, LE Connection Complete, or LE
Enhanced Connection Complete Of Event Incident .

8.3.1.1.1 Broadcast Connection_Handles

Host At the first power on or restart , First send HCI Data packets , Assign a Connection_Handle. thereafter , Use this Handle Go broadcast .

8.3.1.2 AMP Controller Handles

AMP Controllers There are two kinds of ：Logical Link Handles, and Physical Link Handles.

about Host And AMP Controller Between Data,Command and Event operation , If Physical Link Handles To be designated , Then use the Handle, If not specified , When specified Connection_Handle Where to use Logical Link Handles

It's not right here AMP Make a detailed description .

 

8.3.2 HCI Command Packet

HCI Command Packet be used for Host Send a command to Controller controller .

The package format is as follows ：

• OpCode Field

OpCode： Occupy two bytes , Used for command identification , Divided into two domains ：OCF：OpCode Group Field and OGF OpCode Command Field.

• OGF： Occupy high 6bit
• OCF： Occupy low 10bit, among 0X3F Commissioning order for the manufacturer .

• Paramter_Total_Length Field

Paramter_Total_Length： The length of all parameters in the package .

• Paramter Field

 

8.3.3 HCI Event Packet

Every Command After the command is issued , They always bring one Event Return to the status after the command is executed .

The package format is as follows ：

• Event_Code Field

Event_Code： Identify different event types .

• Parameter_Total_Length Field

Parameter_Total_Length： Parameter total length

• Event_Parameter Field

Event_ParameteN： Related parameters

 

8.3.4 HCI ACL Data Packets

HCI ACL Data Packets Specifies the format of the data packet , be used for Host And Controller Data exchange between .

There are two types of packets ：

• Automatically-Flushable： Automatically refresh

Automatically refresh the package , The time of its automatic refresh depends on the set time .

• Non-Automatically-Flushable： Non automatic refresh

Non automatic refresh , The packet will not be refreshed automatically .

The package format is as follows ：

• Handle Field

Handle： As mentioned above , There are several types of this field ：

• Connection_Handle： Used to send packets or segments on the main controller

• Logical_Link_Handle： be used for AMP The controller sends packets

• Physical Link Handles： be used for AMP The controller sends packets

• Flag Field

Flag Include ：PB Flag and BC Flag, namely Packet_Boundary_Flag And Broadcast_Flag, The values are as follows ：

 

8.3.5 HCI Synchronous Data Packets

The packet , Used in Host and Controller Exchange synchronous data between .

The package format is as follows ：

• Packet_Status_Flag Field

This field is associated with Erroneous_Data_Reporting Parameters are related to ：

• If Erroneous_Data_Reporting Parameter set to disable, be Packet_Status_Flag Field set to 00
• If Erroneous_Data_Reporting Parameter set to enable, be Packet_Status_Flag Fields are set according to the following table

• Data_Total_Length Field

 

8.4 HCI Connection package example

HCI Connect command flow ：

1） The Bluetooth protocol stack sends the connection command to the chip ：HCI Connect command

2） The Bluetooth chip reports the command status to the Bluetooth protocol stack ：HCI Command Complete

3） After successful connection , Bluetooth chip reports the successful connection event of Bluetooth protocol stack ：HCI LE Connect complete

 

8.4.1 HCI Connect command

Core5.0 P774

This command is used to make Link Manager Link manager to connect remote devices .

Connect command The packet format is as follows ：

OCF： Here you can see OCF Value , that OGF How much is it worth ？

open Core5.0 P774, We can see HCI_Create_Connection The order belongs to LINK CONTROL COMMANDS Link control command group , This group OGF by 0x01. See Core5.0 P766

For the Link Control commands, the OGF is defined as 0x01.

BD_ADDR： To connect the remote Bluetooth address of the device ,6 Bytes .

Packet_Type： Supported packet types ,2 Bytes .

Page_Scan_Repetition_Mode： Whether to repeat scanning

Clock_Offset： Clock offset between master and slave devices .

Allow_Role_Switch： Whether master-slave role conversion is supported

 

8.4.2 Command Complete Event

When Controller Received Create_Connection command , Will send a Command Complete Event to Host.

The event format is as follows ：

This event is used to return the status after most commands are sent .

Event Code： Event code

Num_HCI_Command_Packets： Set up Host It can be sent to Controller Number of command packages , If not , Is set to 0

Command_Opcode： Indicates the corresponding command code

Return_Parameters： Return the parameters specified by the command

 

8.4.3 Connection Complete Event

This event shows Host And Controller The connection channel between is established successfully .

Event Code： Event code

Status： Connection status

Connection_Handle： After successful connection , Generated Handle value

BD_ADDR： After successful connection MAC Address

Link_Type： Connection type

Encryption_Enabled： Is it encrypted

These parameters are not necessarily required , Here's the catch HCI package , I hope it helps .

 

All right. , The above is the Bluetooth Protocol HCI Detailed introduction of the interface , After a detailed understanding , We have analysis HCI The basic capability of data package ！