Embedded Linux in industrial control applications

4.2 software design for embedded operating system is the core of the entire embedded system.

As mentioned earlier, the embedded system memory and storage capacity is insufficient, you must design for reduction of linux. In the cutting process, the main technologies involved are the following. (1) the streamlining of the standard Linux kernel is oriented to the PC, it integrates many of the needs of the embedded PC system and unwanted features. Therefore, you can add or remove the independence of function block, you can compile the kernel, the only embedded system function modules and remove unnecessary function block. Then, recompile the kernel will be significantly reduced. (2) of the virtual memory system shield after analysis found that virtual memory is the leading Linux real-time is not strong. In the industrial control, certain tasks must meet certain requirements of real-time, shielding the kernel virtual memory management mechanism to enhance real-time Linux. When you want to change the kernel of a mechanism, generally do not have to write code on a large scale, you can use conditional compilation method. At the same time as the linux system on the application process is fair time allocation scheduling algorithm, this algorithm cannot guarantee that the system of real-time requirements, and requirements change. Change the way there are two: one by POSIX, the second is through the underlying programming. The author is linux real-time named pipe (FIFO) queue of special handling real-time task sequencing. In fact, real time named pipe like as never change real-time tasks, so the page can dramatically reduce the memory page without delay caused by uncertainty. (3) written device driver determines the basic functionality of the kernel, is written for a specific device driver, you can follow to write a Linux driver under the rules for writing. Writing a device driver should have the following features: • the initialize and release; • complete data from the kernel to the hardware device delivery and read data from hardware two functions; • read application passed to the device file data as well as the echo application requests for data; • the detection and treatment equipment error. (4) development of Flash-based JFS file system applications and critical data is typically a document to be stored in the Flash file system. JFFS2 file system is a log-structured, which means that it is essentially a long column node. Each node contains information about the parts of the file. JFFS2 is specifically designed for that kind of like flash chip embedded device creation, so it's entire design provides better Flash management with other file systems, incomparable advantages. Follows: ● JFFS2 at sector level Flash erase/write/read operations than Ext2 file system. ● JFFS2 provides better than Ext2fs crash/power-down protection. When you want to change small amounts of data, the Ext2 file system will copy the entire sectors into memory (DRAM), and in memory to be merged into a new data and then written back to the entire sector. But you can always change the JFFS2 need (not override) the entire sector, and also has a crash/power-down function security. Implementation of the above steps, a mini Linux operating system is constructed. Structure of Linux including process management, memory management and document management, etc. It supports multiple tasks in parallel, there is a complete TCP/IP Protocol, while Linux built-in on Ethernet controllers support, you can connect through Ethernet to Ethernet for remote configuration and monitoring. Will crop the good kernel porting to the target Board, first of all should be compiled into the kernel for the processor of the target code. Because of different hardware system of the transplantations boot code will differ, therefore, some kernel program may want to overwrite. Involves writing a Linux boot code and modify the relevant part of the architecture code mainly boot, memory management and interrupt handling. The company will be M-System DOC2000 as system boot device, the boot code can be placed in DOC. This system is powered on, boot code to perform basic hardware initialization, then the kernel image is loaded into memory and runs, in the end, then debug the good kernel and applications programming in Flash memory. Because of this crop of Linux was successfully ported to target platforms, so that you can run the start of the development system, you can apply under specific to developing applications. If the data acquisition module, data processing module, communications and data dissemination module and so on. 5 conclusion today, Internet applications are go to embedded device as the Center, therefore, labor control system combined with the Internet to achieve Internet is an inevitable trend. The embedded Linux kernel embedded microprocessor-based StrongarmSA1110 32-bit MCU system, and then by constructing a TCP/IP multiple network protocols and basic network communication protocols, and then use the embedded operating system on the underlying hardware and network protocols support, as well as on requirements of industrial control system real-time lin-ux kernel and virtual memory mechanisms to ensure the transformation, and control tasks to complete in real-time and reliability. It is foreseeable that this programme in the field of industrial control with good prospects, and a short development cycle, performance stable reliable, adaptable, and so on.