Design of Integrated Communication Control System Based on ARM9 and Linux System

The framework design and function of each module of the multi-function integrated communication control system based on ARM9 hardware platform and embedded Linux system are introduced. The system is POSIX compliant. 1 Standard C language is written, which realizes the collection, analysis and storage of data frames transmitted by the lower computer, and can perform parameters such as serial port baud rate, data time and mobile phone short message number according to the configuration command and data transmission instruction of the upper computer. Configure and store the transfer of data.

With the rapid development of computer technology, industrial data acquisition has evolved from a traditional measurement and control circuit to a modern data acquisition and control system consisting of microcomputers, interface circuits, external general equipment and industrial production objects. However, the data acquisition system with the microcomputer as the core has gradually exposed many defects: large size, not easy to carry; poor scalability and high cost. Therefore, the data acquisition and control system based on embedded system has emerged as the times require. The embedded data acquisition system has the characteristics of high reliability, small size, easy expansion, short development cycle and low cost, which makes it become the communication control in the future. development trend.

1. System working principle and framework

After the storage board is powered on, the program starts with the Socket to first establish the server to wait for the configuration information of the PC. The PC sends the time frame and the mobile phone number frame in sequence. When any one of them does not satisfy the frame format or the verification error, the storage board will go to the PC. The terminal sends the corresponding retransmission command, and the two configuration frames are correctly parsed, then the serial port ttys1 communicating with the lower computer, the serial port ttys2 communicating with the GSM module, and the serial port ttys3 communicating with the PC are set, and then the kernel timer is set. Set the processing of the timeout message to the program that sends the data message, thus implementing the function of sending the SMS notification periodically, and then using the asynchronous I/O function Select to listen to all the input and output. If a message has a message, it will jump to the corresponding In the message processing function, after returning to the Select function, it continues to listen.

2, program module description

The system is mainly composed of a configuration frame processing module and a timing short message group sending module.

2.1 Configuring the Frame Processing Module

The main function of the configuration frame processing module is to receive and parse the configuration frame of the PC. First, the program uses the Socket to establish a connection that the server that satisfies the TCP protocol waits for the connection initiated by the PC. If the connection is received, the first handshake protocol is first customized. After the check is normal, the configuration frame is received. The program determines whether it is a time frame or a mobile phone number frame according to the frame header and the end of the received configuration frame. If it is determined to be a time frame, after the data is verified and verified, the data time is extracted. The serial port baud rate of communication with the PC is placed in the corresponding global variable. If the verification error occurs, the TIme instruction is sent to the PC to indicate that the time frame format error needs to be retransmitted. If it is correct, the success instruction is sent to the PC to indicate that the time frame is successfully received. After receiving the success instruction, the PC starts to send the mobile phone number frame. If the verification error occurs, the PC sends a phone command to the PC. If the mobile phone number transferred to the 5 Byte is correctly converted into the 11-digit mobile phone number represented by the ASCII code, the PC terminal is then sent to the PC. Sending the success command indicates that the mobile phone number frame was successfully received.

2.2 Timed SMS group sending module

The main function of the timed SMS group sending module is to notify the user through the mode of short message after parsing the collected data, which is further divided into: GSM initialization module and short message group sending module. The program sends the AT command to the GSM module through the serial port for the purpose of its control.

2.2.1 GSM initialization module

The main function of this module is to initialize the SMS function of the GSM module and send the information to the user to inform the user that the GSM module is working normally. According to the operation manual of MG323, perform the following steps in sequence before sending the information normally: (1) Send "AT" to confirm that the serial port connected to ARM and GSM module is normal. (2) Send "ATE0" to turn off the echo, so that the command entered during the debugging process will not be printed on the screen after being returned by the GSM module. (3) Send "AT+CPIN" to confirm that the SIM card authentication is successful. (4) Send "AT+CNMI=1,1,2" to set the SMS notification mode. (5) Send "AT+CMGF'=0" and set the SMS format to PDU. (6) Send "AT+CSCA=+8613800290500" and set the short message center number. (7) Send ""AT+CSCS=\"UCS2\" and set the character encoding to USC2.

In GSM, each command returns OK, indicating that the setting is successful, indicating that the GSM module can work according to the set function, the short message is encoded in PDU format, and the general PDU code is composed of A to M13 items: A: short message center address Length, 2 digits hexadecimal number (1 Byte); B: Short message center number type, 2 digits hexadecimal number; C: Short message center number, B+C length will be determined by the data in A; D: File header Byte, 2 digits hexadecimal number; E: information type, 2 digits hexadecimal number; F: called number length, 2 digits hexadecimal number; G: called number type, 2 digits hexadecimal number, The value is the same as B; H: the called number, the length is determined by the data in F; I: protocol identification, 2 digits hexadecimal number; J: data encoding scheme, 2 digits hexadecimal number; K: validity period, 2 digits Hexadecimal number; L: user data length, 2 digits hexadecimal number; M: user data, the length of which is determined by the data in L.

Fill in the A to K fields as required, and the user data is "GSM module initialization success". The Chinese character Unicode conversion tool finds the USC2 code value corresponding to each character and fills it into the M field, and then fills the L field with the Byte as the unit length. At this point, sending the AT command encoded by the PDU format to the GSM module can realize the function of the short message notifying the user that the initialization is successful.

2.2.2 Short message group sending module

Since the GSM initialization module has configured it, the main function of the short message group sending module is to extract the latest frame data stored in the current main data file, and send the short message group that is parsed into data and filled into the PDU format. user. The main difficulty here is to convert the binary representation data into USC2 encoded characters, because the data in the file is stored in Byte, each data occupies 2 bytes, so the 2Byte type is first merged into a short integer to represent a complete data. The conversion converts the binary data into USC2 encoded data, wherein the page height coefficient accounts for 6 bits, the decimal point occupies 1 bit, the decimal point occupies 1 bit, the temperature coefficient occupies 6 bits, the decimal point occupies 1 bit, and the decimal part occupies 1 bit, the above two The integer part of the coefficients is less than 6 bits and is complemented by 0 on the left side.

In order to finally receive data such as 0123.1m in the data received on the short message, the "0" on the left side should be removed, and care should be taken not to remove the "0" in front of 0.01 °C. After processing, the data on the mobile phone text message will achieve good results.

2.3 I / O control module

The main function of the I/O control module is to receive and store the data of the lower computer data and respond to the instructions of the PC, and send data through the network port and the serial port.

Since the system functions of I/O operations such as serial port and network in Linux are blocking functions, if they are used arbitrarily, the program will be blocked in an I/O. The multi-threading implementation can solve the blocking problem, but at the same time The complexity of the code and the problem of multi-threaded synchronization will increase the difficulty of code design. The system adopts single-process design, adopts asynchronous listening function select this function to listen to all input and output ports. If the corresponding port has a message, it jumps into the message processing function, and continues to listen after processing, reaching the single-process processing blocking function. purpose.

The main body of the I/O control module is a select function, which is divided into a serial port serial receiving module according to the input and output, a host computer network port transmitting module and a host computer serial port transmitting module.

2.3.1 lower computer serial port receiving module

The data received by the serial port from the lower computer is first checked and verified. After the verification is correct, it is first stored in the buffer data file and counted. After the upper limit of the buffered data file is reached, the data of the buffer file is copied to the main data file, and the main data is copied. The file is opened in an additional write mode, and the buffered data file is emptied after copying. The method of alternately copying the main data and the buffered data can improve storage efficiency and prevent data loss caused by accidental power failure. The main data file is set to store the soft upper limit. After the main data file is full, the FIFO scheme is adopted. The newly received data from the buffer file is used to unload the main data file and move the file forward, and the starting data is “extruded” to ensure the data file. The chronological order does not exceed the storage soft limit.

2.3.2 Host computer network port transmission module

The network port sending module of the upper computer is mainly the server side, and the software agreement handshake is performed before establishing a connection with the PC, thus ensuring the connection of the application layer is normal. The server uses the principle of "one connection, multiple processing, one release" for the connection request sent by the PC. The communication of data and instructions can be realized perfectly by a single process. After receiving the "transmit" command from the PC, the slave is from the main The data file starts to send data to the PC with an offset of 2048 Byte. After all the data is sent, an "over" command is sent to the PC to indicate that the data has been sent.

2.3.3 host computer serial port transmission module

The serial port sending module of the host computer is similar to the network port sending data module, except that the server is sent to the socket for normal serial port reading and writing. After the data is sent, an "over" command is sent to indicate that the data is sent.

3, the conclusion

The integrated communication control system is implemented on the embedded Linux system. He completed the data acquisition of the lower computer and the command response and data transmission to the upper computer. At the same time, the GSM wireless communication module is used to realize the function of timed short message group sending. This system is powerful, stable and stable. It is a new development platform with high accuracy, high real-time, miniaturization and intelligence. Considering the requirements of industrial control systems for system reliability, flexibility, cost and economic benefits, the embedded system is widely used in communication control and data acquisition.

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