modbusd

Modbus master daemon

• Support doxygen style comments.
• ZeroMQ is a high-level message library, you can replace it with your own data bus implementations without losing the core functionalities.

Table of content

• Continuous Integration
• Design
• Setup
• Documentation

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Continuous Integration

I do continuous integration and build docker images after git push by self-hosted drone.io server for armhf platform , circleci server for x86 platform and dockerhub service.

CI Server	Target	Status
Travis	API
CircleCI	x86
Drone	armhf

Design

Implemented libmodbus function codes

FC	Description	#Len	API
0x01	read coils	2000	int modbus_read_bits(modbus_t *ctx, int addr, int nb, uint8_t *dest)
0x02	read discrete inputs	2000	int modbus_read_input_bits(modbus_t *ctx, int addr, int nb, uint8_t *dest)
0x03	read holding registers	125	int modbus_read_registers(modbus_t *ctx, int addr, int nb, uint16_t *dest)
0x04	read input registers	125	int modbus_read_input_registers(modbus_t *ctx, int addr, int nb, uint16_t *dest)
0x05	write single coil	-	int modbus_write_bit(modbus_t *ctx, int addr, int status)
0x06	write single register	-	int modbus_write_register(modbus_t *ctx, int addr, int value)
0x0F	write multi coils	1968	int modbus_write_bits(modbus_t *ctx, int addr, int nb, const uint8_t *src)
0x10	write multi registers	125	int modbus_write_registers(modbus_t *ctx, int addr, int nb, const uint16_t *src)

Coil/register number and address table

Coil/Register numbers	data address	type	table name	offset	function code
1-9999	0000 to 270E (9998)	Read-Write	Discrete Output Coils	1	1, 5, 15
10001-19999	0000 to 270E (9998)	Read-Only	Discrete Input Contacts	10001	2
30001-39999	0000 to 270E (9998)	Read-Only	Analog Input Registers	30001	4
40001-49999	0000 to 270E (9998)	Read-Write	Analog Output Holding Registers	40001	3, 6, 16

Command mapping table

Command	Number	Description
FC1	1	modbus fc 1
FC2	2	modbus fc 2
FC3	3	modbus fc 3
FC4	4	modbus fc 4
FC5	5	modbus fc 5
FC6	6	modbus fc 6
FC15	15	modbus fc 15
FC16	16	modbus fc 16
SET_TCP_TIMEOUT	50	set tcp timeout
GET_TCP_TIMEOUT	51	get tcp timeout

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Environment variable

• CONF_MODBUSD: config file path

Configuration File

{
    "syslog": 1,
    "zmq":
    {
        "sub": "ipc:///tmp/to.modbus",
        "pub": "ipc:///tmp/from.modbus"
    },
    "mbtcp":
    {
        "connect_timeout": 200000
    }
}

Modbus TCP command format

Please refer to command definition.

External libraries

• libmodbus
• libzmq
• czmq
• uthash
• cJSON

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Library documentations

• uthash user guide
• libmodbus api document
• libmodbus header
• cJSON examples

Flow Chart

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Setup

Setup development dependencies

sudo apt-get update
sudo apt-get install -y git build-essential autoconf libtool pkg-config cmake

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Setup OSS libs dependencies

Install libmodbus library (3.1.4)

git clone https://github.com/stephane/libmodbus/
cd libmodbus
./autogen.sh
./configure
make
sudo make install
sudo ldconfig

Install libzmq (3.2.5)

wget https://github.com/zeromq/zeromq3-x/releases/download/v3.2.5/zeromq-3.2.5.tar.gz
tar xvzf zeromq-3.2.5.tar.gz
cd zeromq-3.2.5
./configure
make
sudo make install
sudo ldconfig

Install czmq (high-level C binding for zeromq)

git clone git://github.com/zeromq/czmq.git
cd czmq
./autogen.sh
./configure
make
sudo make install
sudo ldconfig

Build from source code

git clone modbusd
cd modbusd
mkdir build
cd build
cmake ..
make
./modbusd ../modbusd.json # load external configuration file

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Test Cases

• Test holding registers (4x)
  • 4X Table: 60000 Read/Write uint16 value test: FC6, FC3
  • 4X Table: 30000 Read/Write int16 value test: FC6, FC3
  • 4X Table Multiple read/write test: FC16, FC3
  • 4X Table Multiple read/write test: FC16, FC3
• Test coils (0x)
  • 0X Table Single read/write test:FC5, FC1
  • 0X Table Multiple read/write test: FC15, FC1
• Test Discrete Input (1x)
  • 1X Table read test: FC2
• Test Input Registers (3x)
  • 3X Table read test:FC4
• Test TCP Timeout
  • Set timeout test
  • Get timeout test

Images and testing from the scratch

docker pull edgepro/c-modbus-slave:x86
docker build -t edgepro/modbusd .
docker build -t edgepro/dummy-psmbtcp test/dummy-psmbtcp/.

docker run -itd --name=slave edgepro/c-modbus-slave:x86
docker run -v /tmp:/tmp --link slave -it --name=modbusd edgepro/modbusd
docker run -v /tmp:/tmp -it --link slave edgepro/dummy-psmbtcp

Docker compose

docker-compose up --abort-on-container-exit

Deployment Diagram

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Documentations

• API Documentation

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License

MIT