ARM embedded control system design

1.1 System hardware foundation

The control system is designed based on the Atmel AT91M55800A microprocessor. AT91M55800A is a 16/32-bit microcontroller based on the ARM7TDMI core. Its processor core is a high-performance 32-bit RISC architecture; it has a high-density 16-bit instruction set and extremely low power consumption. It integrates 8 KB SRAM, vector interrupt controller VIC, advanced power management controller APMC and fully programmable external bus interface EBI on the chip; it has 3 USARTs, 58 programmable I/O lines, 6-channel 16-bit timer/counter, 8-channel 10-bit ADC and 2-way 10-bit DAC, providing a highly flexible and cost-effective solution for various ultra-low power applications.

Figure 1 is a hardware block diagram of the control system. The hardware design adopts a structured and modular design concept, which is easy to tailor. The communication interface includes RS232 serial communication interface, Ethernet interface and CAN bus interface. The Ethernet port can be connected to the industrial Ethernet. Combined with the ARM integrated development environment ADSl.2 and the online debugging tool Multi-ICE, the system can be simulated and traced in real time through the JTAG debugging interface and the Embedded ICE logic embedded in the processor.

1.2 System software foundation

(1) Porting of μC/OS-II

The tasks that the control system needs to complete are very complex, there are many peripherals to manage, and the programs are becoming more and more large, so porting an embedded real-time multi-tasking operating system is an inevitable choice. For small real-time control systems, the preemptive real-time multi-tasking operating system μC/OS-II with open source code, solidifiable and customizable, good portability, high stability and high reliability and a preemptive kernel is a good choice. The simple code of μC/OS-II has been applied to embedded systems such as smart meters, information appliances, wireless communication equipment and industrial machines.

It is relatively simple to transplant μC/OS-II to the AT91M5800A processor. Only three files related to the ARM architecture need to be modified: OS_CPU.H, OS_CPU_A.S and OS_CPU_C.C. The code volume is about 500 lines. The specific transplantation process will not be described in detail. There are many successful transplantation examples on the Internet. [page]

(2) Application of IEC 61131-3 standard software

The IEC 6113l-3 standard is the first programming language standard for digital control software technology formulated by the International Electrotechnical Commission (TEC) for industrial control around the world. It includes two parts: programming and common elements. Common elements describe the variables and data types of all common programming elements used in the five programming languages ​​of IEC61131-3 (instruction list, structured text, ladder diagram, function block diagram and SFC), IEC software model and communication model; it provides rules such as how to name these software elements, declare variables, and initialize variables and data types. It is an indispensable organic component for implementing the IEC61131-3 programming system. The programming part describes two important models: the IEC software model and the communication model. These two models constitute the conceptual basis for implementing a programming system that complies with the IEC61131-3 international standard.

The IEC61131-3 standard also defines a standard function and function block algorithm library, and users can also build their own algorithm library. Since the function and function algorithm library are written in ANSI C language, the user's control algorithm program has good portability and reusability.

The application of IEC61131-3 standard software on the hardware platform based on AT91M55800A is to run the IEC runtime system as a task of μC/OS-II. The code is as follows:

2 Serial communication programming

The program written by the user in the programming system based on the IEC6113l-3 standard can be downloaded to the target system (i.e. control system) through the serial port or Ethernet port for execution after compilation and linking. The choice of communication connection between the programming system and the target system is very flexible, which can be RS232 serial communication, Ethernet communication, or other communication methods. The following is the code designed for RS232 serial communication program based on AT9lM55800A.

Create a data receiving/sending buffer in memory:

[page]

Finally, write the interface communication program between the IEC runtime system kernel and the user program:

With the above code, the embedded control system can receive the user IEC program downloaded from the host computer, and the host computer can collect and monitor the real-time data in the control system. These real-time data can also be published to the industrial Ethernet to realize information sharing.

Conclusion

This paper introduces the design and implementation of an embedded real-time measurement and control system based on ARM and IEC61131-3 standards. The system has good openness, scalability and upgradeability. RS232 communication interface, Ethernet interface and CAN bus interface are designed to meet the networking needs of modern industrial control sites. The software programming adopts the IEC61131-3 international standard, which makes the developed user program have good portability and reusability.