Slamtec RPLIDAR A1 Manuel utilisateur

www.slamtec.com

Shanghai Slamtec.Co.,Ltd

RPLIDAR

Low Cost 360 Degree Laser Range Scanner

Interface Protocol and Application Notes

Applied to RPLIDAR A1 & A2

2018-03-08 rev.1.1

 
 
 
 
CONTENTS ...................................................................................................................................................1 
OVERVIEW ...................................................................................................................................................3 
SDK AND DEMO PROGRAM .............................................................................................................................. 3 
PROTOCOL BASICS ....................................................................................................................................4 
BASIC COMMUNICATION MODE........................................................................................................................ 4 
REQUEST PACKETS’FORMAT........................................................................................................................... 6 
RESPONSE PACKETS’FORMAT......................................................................................................................... 7 
WORKING STATE AND MECHANISM................................................................................................. 10 
MAJOR WORKING STATES AND TRANSITION CONDITIONS ............................................................................ 10 
SCANNING STATUS........................................................................................................................................... 11 
REQUEST AND RESPONSE DATA......................................................................................................... 12 
REQUESTS OVERVIEW....................................................................................................................................... 12 
STOP REQUEST................................................................................................................................................ 12 
RPLIDAR CORE RESET(RESET) REQUEST ...................................................................................................... 13 
START SCAN（SCAN）REQUEST AND RESPONSE......................................................................................... 13 
EXPRESS SCAN(EXPRESS_SCAN) REQUEST AND RESPONSE ........................................................................ 17 
FORCE SCAN(FORCE_SCAN) REQUEST AND RESPONSE............................................................................... 23 
GET DEVICE INFO (GET_INFO) REQUEST AND RESPONSE ............................................................................. 24 
GET DEVICE HEALTH STATUS (GET_HEALTH) REQUEST AND RESPONSE ..................................................... 26 
GET SAMPLE RATE(GET_SAMPLERATE) REQUEST........................................................................................ 27 
APPLICATION NOTES ............................................................................................................................. 28 
RETRIEVING SCANNING DATA FROM AN RPLIDAR ......................................................................................... 28 
CALCULATE RPLIDAR SCANNING SPEED........................................................................................................ 29 
REVISION HISTORY ................................................................................................................................. 31 
APPENDIX .................................................................................................................................................. 32 
IMAGE AND TABLE INDEX ................................................................................................................................. 32 
Contents 

3/ 32

The host system communicates with RPLIDAR core system via the TTL UART serial

interface. Based on the communication protocol defined in this document, the host

system can retrieve the scan data, the device status, the health information etc. and

manipulate RPLIDAR’s working mode.

Figure 1-1 The Communication Between RPLIDAR and Host System

Please refer to the RPLIDAR datasheet for information about the bottom layer

communication protocol and the electrical level definition of the serial signals used

to communicate with RPLIDAR. The communication protocol based on UART serial

port and the data transmission format will be introduced in this document.

SDK and Demo Program

SLAMTEC provides open-sourced SDK and demo program for customers to

integrate RPLIDAR into their systems quickly. The SDK implements all the

communication stacks, driver logics and related data structures described in this

document

The SDK supports multiple platforms including Windows, Linux, MacOS and even

bare systems without an OS.

Please refer to the SDK manual for details.

Overview

GND

Host System

4/ 32

Basic Communication Mode

The RPLIDAR uses a non-textual binary data packet based protocol to communicate

with host systems. And all the packets transmitted on the interface channel share

uniform packet formats.

A communication session is always initialized by a host system, i.e. a MCU, a PC, etc.

RPLIDAR itself won’t send any data out automatically after powering up.

If a data packet is sent from host systems to RPLIDARs, such a packet is called a

Request. Once an RPLIAR receives a request, it will reply the host system with a data

packet called a Response.

RPLIDAR will only start performing related operations required by a host system

once after it receives a request. If RPLIDAR should reply to the host system, it will

send one or more required response packets.

In order to let an RPLIDAR start scanning operation and send out data, a host system

is required to send a pre-defined Start Scan request packet to RPLIDAR. RPLIDAR

will start scanning operation once after it receives the request and the scan result

data is sent out to the host system continuously.

There are three different request/response modes based on the related request

types:

Request/Response Modes

Figure 2-1 RPLIDAR Request/Response Modes

Protocol Basics

RPLIDAR

Host System

Send a Request Packet

Perform

Some

Operation

Reply a Response Packet

Waiting for

Response

Another Request

5/ 32

Host system should prevent sending extra request packets if the RPLIDAR is busy

with handing the current request and hasn’t replied to the host system yet.

Otherwise,

these extra request packets will be discarded by the RPLIDAR’s protocol stack and

the RPLIDAR will not have any chance to handle it.

Single Request-Multiple Response Modes

This mode is used when the RPLIAR is asked to perform the scan operation. After a

host system sending a Start Scan request, RPLIDAR will take distance scan

measurement continuously. Once a scan measurement sample is retrieved, its

related result data (distance, angle value) will be sent out as individual response

packets.

Host systems are only required to send a single request packet with this mode but

will receive a continuous response packet stream with multiple response packets.

Figure 2-2 RPLIDAR Single Request - Multiple Response Mode

The host system can interrupt RPLIDAR and let it leave the multiple responses mode

by sending a STOP request or any request packet. After leaving the multiple

RPLIDAR

Host System

Send a Start Scan

Request

Initialization

Reply a response descriptor

Waiting for

response

Prepare for

receiving

Scan

Operation

Measurement Sample1

Measurement Sample2

Receiving data

…

Measurement Samplen

Another response

Exit the scan

operation

Handle other

responses

6/ 32

responses mode, the RPLIDAR will continue to handle the request which has

interrupted it.

The request packets sent by the host system during the multiple responses mode

will be cached by the RPLIDAR’s protocol stack. After leaving the multiple responses

mode, RPLIDAR will handle the cached request.

Single Request-No Response

For requests like STOP, RESET Core, RPLIDAR uses the single request –no response

mode since there is no need to reply to the host system.

Host systems should wait for a period of time before sending another request since

RPLIDAR needs time to process the request operation. Otherwise, the request may

be discarded by the RPLIDAR’s protocol stack.

Figure 2-3 RPLIDAR Single Request-No Response Mode

Request Packets’ Format

All request packets sent by a host system share the following common format. Little

endian byte order is used.

Figure 2-4 RPLIDAR Request Packets’ Format

RPLIDAR

Host System

Send a Request Packet

Perform

some

Operation

Waiting for

response

Another request

Start Flag

Command

Payload Size

Payload Data

Checksum

1byte

(0xA5)

1byte

0-255 bytes

1byte

Optional Section

Transmission Order

≤5 seconds

7/ 32

A fixed 0xA5 byte is used for each request packet, RPLIDAR uses this byte as the

identification of a new request packet. An 8bit (1byte) command field must follow

the start flag byte.

If the current request carries extra payload data, an 8bit (1byte) payload size field is

required to be transmitted after sending the command field and then follows the

payload data. After the payload data has been transmitted, an 8bit (1byte) checksum

field calculated from the previous sent data should be transmitted.

The checksum value can be calculated using the following equation:

  󰇟󰇠󰇟󰇠

Note: Timing Consideration

All bytes within a request packet must be transmitted to RPLIDAR within 5 seconds.

Otherwise, the communication stack of RPLIDAR will discard the current request

packet.

Response Packets’ Format

All the response packets are divided into two classes: response descriptors and

data responses. If the current request received by RPLIDAR requires a response,

RPLDAR will always send a response descriptor packet first and then send one or

more data response packets based on the type of requests. Only one response

descriptor packet will be sent out during a request/response session. The response

descriptors carry the information of the incoming data responses. All the response

descriptors share a same format.

8/ 32

Figure 2-5 Response Packets Sent during a Single Request-Single Response Mode

Figure 2-6 Response Packets Sent during a Single Request-Multiple Response Mode

The format of response descriptors is depicted in the following figure.

Figure 2-7 RPLIDAR Response Descriptors’ Format

RPLIDAR

Host System

Request #1

Response Descriptor

Data Response

Request #2

…

RPLIDAR

Host System

Request #1

Response Descriptor

Data Response

Request #2

…

Data Response

…

Start Flag1

Start Flag2

Data Response Length

Send Mode

Data Type

1byte (0xA5)

1byte (0x5A)

30bits

2bits

1byte

Transmission Order

9/ 32

A response descriptor uses fixed two bytes’ pattern 0xA5 0x5A for the host system

to identify the start of a response descriptor. The 30bit Data Response Length field

records the size of a single incoming data response packet in bytes. (All the

incoming data response packets within a request/response session should have the

same format and length). The 2bits Send Mode field describes the request/response

mode of the current session. Its values are listed below:

Figure 2-8 RPLIDAR Data Response Packets Value

The 1byte Data Type describes the type of the incoming data response packets. It

is related to the type of the request RPLIDAR just received. Host systems can choose

different data receiving and handling policy based on this field.

Different from response descriptors, there is no common format used among

response data packets. Each type of response data has its own data format and

packet length based on its type.

Send Mode

Description

0x0

Single Request –Single Response mode, RPLIDAR will send only one data

response packet in the current session.

0x1

Single Request –Multiple Response mode, RPLIDAR will continuously send

out data response packets with the same format in the current session.

0x2

Reserved for future use

0x3

Reserved for future use

10 / 32

Major Working States and Transition Conditions

RPLIDAR has the following 4 major states: Idle, Scanning, Request Processing and

the Protection Stop state.

The translation conditions are depicted in the following figure:

Figure 3-1 RPLIDAR’s Major Status Translation

The Idle state is the default state of RPLIDAR which will be entered automatically

after powering up or reset. Both the laser diode and the measurement system are

disabled in this state, and the whole system is in power saving mode. Once RPLIDAR

enters the Scanning state, the laser diode and the measurement system will be

enabled and RPLIDAR will start measuring distance and sending the result out

continuously.

RPLIDAR will enter the Request Processing state once it receives request packets

from the host system. During processing the request, RPLIDAR won’t perform the

scan operation and won’t send any data out. It will only send out response data for

request needing a response after the required operation has been finished. After

the request has been processed, RPLIDAR will enter other status specified by the

request.

Once RPLIDAR detects something wrong with the device hardware, it will stop the

current operation and enter the Protection Stop state. A host system can still

communicate with an RPLIDAR in the Protection Stop state to query its working

Working State and Mechanism

Idle

Scanning

Request

Processing

Protection

Stop

Reset the core system

No Request

Request

No failure

System Power Up

Request comes

Partial Requests

Start Scan Request

Request comes

Failure detected

Autres manuels pour RPLIDAR A1

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