Simple Serial

A simple library for communication over serial interfaces. It can be used for microcontroller to microcontroller communication or computer to microcontroller communication.

Currently supported platforms:

Arduino / C++
Python

This is a repository for the Python version. Find Arduino / C++ version at: https://github.com/nplan/simple_serial_arduino

The library supports simple and efficient transfer of data types:

Integer (signed, 32 bit)
Floating point (32 bit)
Strings

Custom data types can be easily added.

Installation

Setup

Install using pip:

pip install git+https://github.com/nplan/simple_serial_python.git

Don't forget to use pip3 if you have multiple python versions installed.

Usage

Data is sent in packets. Each packet has an id in range 0 - 255. The id can be used for identifying the topic of the packet.

from simple_serial import SimpleSerial, bytes2int, bytes2float, bytes2str

# Open communication
s = SimpleSerial(port="/dev/cu.SLAB_USBtoUART", baud=115200)
s.open()

# Send some data
s.send(id=1, payload=12345)  # Send packet with id 1 containing an integer
s.send(2, 2.345)  # Send packet with id 2 containing a float
s.send(3, "this is a string")  # Send packet containing a string

# Receive data in a loop
while True:
    id, payload = s.read()  # Returns a packet from received buffer
    if id == 123:
        # do something

# Register a callback that is called automatically when a packet with
# certain id is received.
# Payload is passed as argument to the callback function.
s.set_callback(id=30, callback=myFun)


# Convert payload from bytes to desired type
    id, payload = s.read()
    val = bytes2int(payload)  # convert to integer
    val = bytes2float(payload)  # convert to float
    val = bytes2str(payload)  # convert to string
    # Note: there is no way to know of what type the data inside a packet is.
    # You should use id to differentiate between packets.

The default payload length in bytes is set to 8. This can be changed by passing argument payload_max_len to SimpleSerial() constructor.

How it works?

Before being sent over serial port, data is framed into packets using using special flag bytes:

START Byte - Signalling start of packet, default = ASCII 2 STX
END Byte - Signalling end of packet, default = ASCII 3 ETX
ESC Byte - Inserted prior to payload data byte if it happens to have the same byte value as one of the flag bytes. default = ASCII 1 SOH

A complete packet frame:

BYTE 0	BYTE 1	BYTE 2	BYTES 3 ... N-2	BYTE N-1	BYTE N
START	LEN	ID	Payload Data Bytes	CRC	END

Byte 1 LEN indicates the total length of packet in bytes.

When SimpleSerial.send() functions is called, the payload is framed into a packet and placed into send queue. Packets from this queue are sent over serial port using a separate thread.

Serial port is being monitored for incoming packets inside a separate thread. The thread reads incoming packet frames byte by byte. When a complete packet frame is received, it is placed into read queue. Packets are retrieved from this queue using function SimpleSerial.read().

The length of send and read queues is set by argument queue_max_len of SimpleSerial() constructor. If a queue is full, packets are discarded (not sent or not received).

Testing

A number of test are implemented that verify the core functionality of the library by using a loopback serial interface. You can use pytest to run the tests.

For testing communication with external devices running Arduino / C++ implementation of this library transmission_tester.py script is implemented. You can use it by running:

python3 -m simple serial.transmission_tester <port> <baud>