Design of intelligent safe based on AT91SAM9260

The system can be divided into three layers from the inside to the outside: operating system layer, task layer and hardware circuit layer, as shown in Figure 3. The embedded operating system is the control center of the embedded system's software and hardware resources. It organizes multiple tasks to share the resources of the embedded system. Common embedded real-time operating systems include Window CE, VxWorks, μC/OS-Ⅱ, Linux, etc. The latter two operating systems have free open source codes.

2.1 Embedded operating system solution selection

In order to select a suitable embedded operating system, this paper analyzes and compares the process scheduling, file system support and system porting of the open source μC/OS-Ⅱ and Linux operating systems, because these are the key factors in the design, application and porting of embedded operating systems.

(1) Process Scheduling

Process scheduling is the competition for the use of internal resources of the computer system by multiple tasks in the operating system coordination scheduling system. As a real-time operating system, μC/OS-Ⅱ adopts a preemptive real-time multitasking kernel, which runs the highest priority task that is ready at any time. μC/OS-Ⅱ can support up to 64 tasks. It searches for the highest priority task through the ready task table and performs task switching.

The Linux operating system suspends the process at regular intervals, and the system generates fast and periodic clock timing interrupts, and determines the called process through the scheduling function. The task_struct structure of each process in the Linux operating system has five parameters: scheduling policy, static priority, dynamic priority, time slice, and real-time priority. Linux distinguishes between real-time processes and ordinary processes based on the scheduling policy, and real-time processes run before ordinary processes. The Linux operating system uses different standards to select processes for different processes of the same type:

① Ordinary process scheduling. When the scheduling policy value is SCHED_OTHER, it is an ordinary user process. Linux uses the dynamic priority scheduling standard, and the basis for selecting the process is the value of the process time_sli-ce.

② Real-time process scheduling. For real-time processes, Linux uses two scheduling strategies, namely first-come-first-served scheduling and time slice round-robin scheduling. When the scheduling strategy value is SCHED_FIFO, the first-come-first-served scheduling rule is used. When the scheduling strategy value is SCHED_RR, the time slice round-robin scheduling rule is used, that is, the CPU is released when the time slice is used up, and the process is placed at the end of the waiting queue.

(2) File system

The file system is responsible for accessing and managing file information. In embedded systems, common file systems include YAFFS, JFFS2, CramFS, RamFS, Ramdisk, etc.

The μC/OS-Ⅱ operating system itself does not support the file system. Although μC/OS-Ⅱ has good scalability and can expand its support for the file system if necessary, it will increase the development workload.

The Linux operating system has a complete file system and network advantages. It can easily support network file systems and has built-in TCP/IP protocols, which makes it convenient for Linux to develop network access devices.

(3) Operating system migration

Embedded operating systems must be ported before they can run on different microprocessors. Both μC/OS-Ⅱ and Linux provide open source code, and their structured design is easy to tailor, so they can be ported to new processor platforms.

① Porting of μC/OS-Ⅱ. To port the μC/OS-Ⅱ operating system, the target processor must meet the following requirements: the processor's C compiler can generate reentrant code, and interrupts can be turned on and off using C language; the processor has sufficient storage capacity as a task stack in a multi-tasking environment; the processor has instructions to read and store stack pointers and registers into the stack or memory. Therefore, the porting of μC/OS-Ⅱ only requires modifying the relevant codes between different processors according to the above requirements.

②Linux porting.

First, the system is initialized: turn off Watchdog, change the system clock, initialize the storage controller, and copy the operating system kernel to the memory. This series of operations is called BootLoader. Usually, U-boot is transplanted to realize the function of BootLoader; secondly, Linux kernel transplantation is performed: download the kernel source code, cut and configure the kernel, compile the kernel to generate an image file, and download it to the target board; finally, the file system is transplanted: generate the root file system directory, transplant Busybox, generate an image file, and download it to the target board. In summary, both μC/OS-Ⅱ and Linux have open source code and meet high real-time requirements. μC/OS-Ⅱ is a compact real-time operating system. Its kernel provides functions such as task scheduling and management, time management, synchronization and communication between tasks, memory management and interrupt services. The minimum kernel can be compiled to 2 kB, and the kernel only occupies 6 to 10 KB after all functions are compiled. Although μC/OS-Ⅱ has high execution efficiency, small footprint, excellent real-time performance, and strong scalability, the μC/OS-Ⅱ system lacks support for the file system, so μC/OS-Ⅱ is suitable for applications with limited storage resources and small control systems. However, Linux has multi-tasking, customizable kernel, perfect network communication, graphics and file management mechanism, can support a large number of peripheral hardware devices and other functions, its performance is efficient and stable, and the development and transplantation environment is good. In view of the fact that the system needs to complete multiple task control and file management, and has abundant storage resources, and also considering the future network expansion, Linux was selected as the embedded operating system.

2.2 Task Layer

For applications managed by the Linux operating system, firstly, relatively independent sub-function modules are divided according to the system functions. Each module is a task, and each task is composed of several sub-tasks. The scheduling between tasks is determined by the Linux kernel scheduler. The tasks divided by the system include:

① Read/write UART0 task. It is mainly responsible for interacting with the host PC, parsing and executing the control commands sent by the host PC, and returning the results of the execution to the host PC.

② Read/write UART1 camera task. When the user inputs the fingerprint, the fingerprint reader is activated to receive the fingerprint data, the camera is activated, and the user is photographed. After the cabinet door is closed, the RFID reader is activated to collect the file ID information in the cabinet and compare it with the last information to obtain the information of the items borrowed and returned by the user after this operation.

③ Recording task: When the UART1 task completes the RFID reader's collection task, the task will store the user's fingerprint information, the time of opening and closing the cabinet door, the user's head portrait, and the ID of the borrowed and returned files.

④ Cabinet door opening and closing task: After the fingerprint data is identified, the fingerprint data is compared with the data in the authorized fingerprint library, and the unlocking operation is performed if the match is successful.

⑤Alarm task: Cycle the vibration sensor and activate the alarm if abnormal vibration is found.

After writing the codes for these tasks and starting the operating system, the application starts running. To extend other functions, just add the corresponding tasks.

3 Conclusion

The experimental results show that the system meets the users' confidentiality needs, has real-time processing capabilities, and is easy to expand. The selected Linux multi-tasking real-time operating system provides good support in process scheduling, file system management, etc.