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This article mainly explains "how to write the communication protocol in Qt". The content in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "how to write the communication protocol in Qt".

I. Preface

Communication protocol parsing is the core soul of the whole system, most people do software and hardware communication development, the first step is to write demo to parse the protocol, and then slowly write the whole interface and operation flow, etc. In the field of industrial control, modbus protocol is still widely used, this system also uses modbus protocol, using this protocol can be easily accessed with some third-party configuration software, and the compatibility is stronger. Modbus is only a protocol standard, as for the use of serial port or network or other, it is implemented by the manufacturer. Generally speaking, systems using modbus protocol support 255devices to communicate on the same network, and most of them will use the modbus half-duplex mechanism to poll the device status one by one. Each communication link is either sending data or receiving data, and cannot be carried out at the same time. One advantage of this is that the transmission distance can generally reach 1200 meters, but if it is a full-duplex serial port, it will basically stop at 100m, depending on the baud rate, except if you can use a transit device to forward it.

The project supports serial devices and network devices, add the corresponding communication port in the port management, modbus communication protocol analysis library, there is a third-party open source libmodbus, cross-platform, Qt from Qt5.8 to add a bus serialbus library, including QModbusClient and QModbusServer to do modbus protocol parsing, I have used both, more or less the same, the method of use are similar, on the whole, libmodbus is better than the modbus that comes with Qt. However, for greater flexibility, this project uses its own program to parse protocol data, so that it does not have to worry about the meaning of those interfaces that are sent a few bytes at a time in the encapsulated interface, and it is also very convenient to parse on its own. All the modbus communication projects I have written use their own protocol parsing.

II. Functional features

Collect data port, support serial port + network port, serial port support free setting of serial number + baud rate, network support free setting of IP address + communication port, each port supports collection cycle, default one address per second, support setting communication timeout times, default 3 times, support maximum reconnection time, used to re-read offline devices.

Controller information, you can add the controller name, select the controller address + controller model, and set the number of detectors under the controller.

Detector information, can add tag, free to choose detector type, gas type, gas symbol, high reported value, low reported value, buffer value, clear zero value, whether enabled, alarm sound, background map, storage cycle, numerical conversion decimal places, alarm delay time, alarm type (HH,LL,HL) and so on.

Controller model + detector type + gas type + gas symbol, all can be configured freely.

Maps can be imported and deleted, and all detectors can be dragged and saved freely.

Port information + controller information + detector information, support import and export + export to excel+ printing.

Run record + alarm record + user record, support multi-condition combination query, such as time period + controller + detector, etc., all records can be exported to excel+ printing.

Records exported to excel support all versions of table files such as excel+wps and do not rely on software such as excel.

You can delete data within a specified time range, support automatic cleaning of early data, and set the maximum number of saved records.

Support alarm short message forwarding, support multiple receiving mobile phone numbers, you can set the sending interval, such as instant sending or sending all alarm messages once every 6 hours, the text message content is too long, automatically split multiple text messages.

Support alarm email forwarding, support multiple receiving mailboxes, can set sending interval, such as immediate sending or sending all alarm messages once every 6 hours, support attachment sending.

Overreport color + underreport color + normal color + 0 value color + curve background + curve color, etc., are free to choose.

The Chinese title + English title + logo path + copyright of the software can be set freely.

Provide switch settings for boot operation + alarm sound + automatic login + remember password and so on.

Alarm sound can be set to play the number of times, the interface provides 17 kinds of skin file selection.

Cloud data synchronization is supported, and the information of cloud database can be set, such as database name, user name + password, etc.

Support network forwarding and network reception, after the network reception is turned on, the software receives data from udp for analysis. Network forwarding supports multiple target IP, so it realizes the software of local collection, and freely transfers the data to the client to view the detector data at any time.

Automatically remember the user's last stay in the interface + other information, restart and apply automatically.

The alarm automatically switches to the corresponding map, and the detector button flashes.

Double-click the detector icon to control it back.

Support user rights management, administrator + operator two categories, user login + user exit, can remember the password and automatic login, more than three error messages and close the program.

Support four monitoring modes, equipment panel monitoring + map monitoring + table data monitoring + curve data monitoring, free to switch, four synchronous applications.

Support alarm relay linkage, a tag can link multiple modules and relay numbers across serial ports, and support many-to-many.

The local data store supports sqlite+mysql and remote data synchronization to the cloud database. Automatically reconnect.

The data collected by the local device is uploaded to the cloud in real time so that it can be extracted by other methods such as APP or web.

Two kinds of data sources are supported, one is serial port and network to collect equipment data through protocol, the other is database collection. The database acquisition mode can be used as a general system.

Comes with a device simulation tool that supports 16 device data simulations, as well as database data simulations to test data when there is no device.

The default communication protocol uses modbus protocol, and later increases the support of mqtt and other Internet of things protocols to make a general system.

Supports all windows operating systems + linux operating systems and other operating systems.

Third, effect picture

4. The core code void DeviceClient::checkValue () {if (! isOk) {return;} QMutexLocker locker (& mutex); readData (); / / at least how many bytes are needed to ensure that the following data is fetched without error int size = buffer.size (); if (size < 5) {return } / / 01 03 08 00 00 00 95 D7 / / 01 03 08 00 14 03 12 00 00 00 79 E6 / / take out the first byte to determine whether it is the address quint8 addr = buffer.at (0) in the current address set; quint8 cmd = buffer.at (1); quint8 len = buffer.at (2); / / if it is an error code, parse the error message QList cmds; cmds directly

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