Design of remote monitoring module based on embedded Linux and Arm

Introduction
Embedded systems are application-centric, computer-based systems with tailorable software and hardware to meet the strict requirements of application systems for functions, reliability, cost, volume, and power consumption. Among them, the design of remote configuration modules based on embedded Linux has attracted more and more attention. Through the design of remote configuration modules based on embedded Linux, remote experts and related technicians can monitor the operating status of devices connected to the server from any node on the Internet and perform operation modifications. The
main function of the system is to enable remote experts and related technicians to monitor the operating status of multiple devices through the client side of the system in different locations through computers. The server side of the system on the device side not only undertakes some tasks of real-time detection of system status, but also needs to save these recorded information and process the requests issued by the client software accordingly. The system has expanded the network card module, input and output signal interface and other modules in hardware to meet the needs of remote control.

1 System hardware design
This system uses Samsung's S3C44BOX ARM7TDMI core as the microprocessor chip. The system hardware framework structure diagram is shown in Figure 1, and its circuit schematic diagram is shown in Figure 2.

1.1 Storage Module Design
The system's FLASH uses HY29LV160, with a capacity of 2M bytes, which serves as the program memory of S3C44BOX. It stores boot code, uclinux kernel, Ethernet MAC address, and application programs. The single-chip storage capacity of HY29LV160 is 16M bits (2M bytes), the operating voltage is 2.7V~3.6V, and it uses 48-pin TSOP package or 48-pin FBGA package. It has a 16-bit data width and can work in 8-bit (byte mode) or 16-bit (word mode) data width. In the design process of this system, considering that the maximum capacity of the uclinux operating system with application programs will not exceed 1_7 MB, the FLASH memory with a size of 2MB can meet the system requirements. The DRAM uses HY57V641620, which is used to set the program stack and store various variables. The storage capacity of HY57V641620 is 4 groups x 16 M bits (8 M bytes), and the operating voltage is 3.3 V. According to the system requirements, a 16-bit or 32-bit SDRAM memory system can be constructed. However, in order to give full play to the data processing capability of the 32-bit CPU, the system uses a 32-bit SDRAM memory system with a total of 16 MB of SDRAM space, which can meet the operating requirements of embedded operating systems and various relatively complex algorithms.
1.2 Network interface module design
The network interface chip of the system is RTL8019AS. It is a 10 M Ethernet chip that can provide Ethernet access for the system. The data bus width of RTL8019AS is 16 bits. Therefore, the IOCS16B pin is pulled up in the design. RTL8019AS integrates two RAMs. One is 16 kB, with an address of 0x4000-7FFF; the other is 32 bytes, with an address of 0x0000-0x001F. 16k RAM is used as a buffer for sending and receiving data. Generally, 0x4000-0x46FF is used as a sending buffer, and 0x4700-0x7FFF is used as a receiving buffer. The interrupt output INTO of RTL8019 is connected to the EINTO terminal of S3C44BOX. In this way, the external interrupt O of the processor can be used to report the current operation of CPURTL8019AS, such as sending and receiving data, error exceptions, etc. The system can query the value of the internal register ISR of RTL8019 to obtain the operating status of the system for reading. [page]

I0S2 is pulled up, and the others are left floating. When the pin of RTL8019AS is left floating, the input state of the pin is low level. There is a 100 kΩ pull-down resistor inside, so IOSO, IOSI, and I0S3 are all low level, and the I/0 base address of the chip is 200H. Chip select AEN is connected to nGCS5 of the processor, which is Bank5, so the address range allocated by RTL8019 in the system is: 0xoa000000—0xoc000000. Since the data bus width is 16 bits, the A1 of the processor is connected to the SA0 of 8019, so for the processor, the I/0 base address of RTL8019AS is 0XOA000400H. 20F001 is a network card filter, which contains a pair of low-pass filters and a pair of isolation transformers. It is directly connected to the RJ45 crystal socket.

2 Construction of system software platform
After modifying the standard Linux kernel, uclinux has formed a highly optimized and compact embedded Linux. Although it is small in size, uclinux still retains most of the advantages of Linux: stability, good portability, excellent network functions, complete support for various file systems, and standard and rich APIs, which are suitable for the establishment of remote configuration modules. Therefore, the remote configuration module is based on uclinux to establish the system software platform.
The system uses the GNU suite arm-elf tool chain: arm-elf-tools-20030314. sh to establish a cross environment for compiling uclinux. Copy arm-elf-tools-20030314. sh to the root directory and run the installation:
sh arm-elf-tools-20030314. sh to compile and port uclinux .
After the cross compilation is successful, the images directory is generated under the uClinux-dist/directory, which contains 3 binary files: image. ram, image. rom and romfs. img.

3 System software design
The system software is the core of the remote configuration module. First, the bootloader process is written to optimize the execution of the system on the development board, and then the application and device driver development are implemented. The application development is mainly based on the writing of the socket application. In the process of socket implementation, this system uses xml files to configure device driver parameters.
3.1 Bootloader design
The design of the bootloader is mainly to jump the system program execution to the execution location of the system kernel after the system is powered on and reset. For this main function, the kernel and other parts of the microprocessor must be initialized and other functions must be expanded. The bootloader mainly completes the following processes:
(1) Establish an interrupt vector table
(2) Initialize various processor modes
(3) Introduce special variables
(4) Initialize memory
(5) Code copy
After completing the system hardware initialization process, the CPU usage right is handed over
to the operating system, thus completing the ultimate purpose of the bootloader.
3.2 Device driver development
Linux operation of devices The Linux system accesses devices just like accessing files
. For example, to open a device, use the system call open()