Skip to main content

Implements a StructuredPacket for pySerial's serial.threaded module

Project description

build-status Latest version released on PyPi

Installation

$ pip install serialstruct

Motivation

When sending a structured binary packet over Serial, the only way (that I’m aware of) to guarantee packet alignment with arbitrary data is to send a header that’s larger than any of the elements and add padding between each element. Here’s an example:

struct Packet {
        int sensor1;
        int sensor2;
}

If we send this over the wire and start reading at an arbitrary time, it’s impossible to know what byte of the packet we’re reading. To mitigate this we can add a header and some padding.

struct Packet {
        char header[5]; // Any sequence without a '\0'
        int sensor1;
        char pad1;      // '\0'
        int sensor2;
        char pad2;      // '\0'
}

Now we just need to wait until the header sequence is read and we can consume the rest of the packet without worrying about alignment.

pySerial only implements a FramedPacket which expects a unicode sequence that starts with a ‘(‘ (0x28) and ends with a ‘)’ (0x29). This means the bytes 0x28 and 0x29 cannot appear anywhere in the binary data.

Usage

Subclass serialstruct.StructuredPacket to specify the data size in the packet and to implement the handle_packet() callback function.

import struct

import serial
import serialstruct
import time


PACKET_STRUCT = struct.Struct("<IxIx")

class MyPacket(serialstruct.StructuredPacket):

    DATA_SIZE = 10 # Excluding header: 4+1+4+1

    def __init__(self):
        super(MyPacket, self).__init__(self.DATA_SIZE)

    def handle_packet(self, packet):
        print(PACKET_STRUCT.unpack(packet))

    def send_packet(self, packet):
        self.transport.write(self.HEADER)
        self.transport.write(packet)


ser = serial.serial_for_url("loop://", baudrate=115200, timeout=1)
with serial.threaded.ReaderThread(ser, MyPacket) as protocol:
    # unsigned int, pad, unsigned int, pad; with no alignment
    packet = PACKET_STRUCT.pack(1, 2)
    protocol.send_packet(packet)
    time.sleep(1)

Prints:

(1, 2)

Project details


Release history Release notifications

This version
History Node

1.1.0

History Node

1.0.24

History Node

1.0.23

History Node

1.0.22

History Node

1.0.21

History Node

1.0.20

History Node

1.0.19

History Node

1.0.18

History Node

1.0.17

History Node

1.0.16

History Node

1.0.15

History Node

1.0.14

History Node

1.0.13

History Node

1.0.12

History Node

1.0.11

History Node

1.0.10

History Node

1.0.9

History Node

1.0.8

History Node

1.0.7

History Node

1.0.6

History Node

1.0.5

History Node

1.0.4

History Node

1.0.3

History Node

1.0.2

History Node

1.0.1

History Node

1.0.0

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, size & hash SHA256 hash help File type Python version Upload date
serialstruct-1.1.0.tar.gz (4.3 kB) Copy SHA256 hash SHA256 Source None Apr 27, 2017

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging CloudAMQP CloudAMQP RabbitMQ AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN DigiCert DigiCert EV certificate StatusPage StatusPage Status page