With the wide application of network technology and multimedia technology, digital network video has developed rapidly. In the field of network video conferencing and network monitoring, traditional analog video signals are converted into digital video signals, and with the help of existing IP networks. Transmission has become a hot spot today.
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In terms of technical implementation, it is usually implemented by using a network camera. Currently, there are two types of network cameras on the market: one is a common camera plus a video gateway, but this solution is bulky and cumbersome; the other is Integrating all network access functions into the camera, it is small, full-featured, easy to use and maintain. There are many solutions for the rear-type camera. This paper proposes a design based on embedded DSP and gives specific Hardware and software implementation.
1 hardware system design
1.1 embedded processor TMS320DM642
TMS320DM642 (hereinafter referred to as DM462) is a new generation multimedia processor recently released by TI. It is based on its second-generation high-performance VelociTI VLIW structure and is suitable for a variety of digital media applications. The DM642 has a clock frequency of 600MHz and a command speed of up to 4800MIPS. The two features of this DSP are: first, with three configurable video interfaces (VP), which can simultaneously acquire three video signals; second, integrated with Ethernet interface, 10/100Mbps mode adaptive, capable Working in full-duplex or half-duplex mode with hardware flow control and Quality of Service (QoS) support. The DM642 is very powerful and it is one of the best platforms for multimedia communication systems.
1.2 hardware overall architecture
The hardware platform of the system consists of six parts, namely video acquisition, data storage, video processing, video display, network and power management. The block diagram is shown in Figure 1.
The video acquisition part adopts analog PAL camera and digital image with high-precision video A/D converter. The A/D converter adopts TI's TVP5145 chip, its sampling precision reaches 10bit, and the output supports CCIR-656 and BT656 formats.
The data storage part of the RAM uses Samsung's SDRAM. To match the DM642's 64-bit EMIF (external memory interface), four SDRAMs are used, each working in 16-bit mode, with a single-chip capacity of 32MB. The ROM of the data storage part uses ATMEL. The company's NOR type Flash chip has a total capacity of 256KB and a data bus of 8 bits. The SDRAM in this system is used to store the system runtime code and temporary image data. Flash is used to save the system self-starting code and system program code.
The video display part adopts digital LCD, which can save the digital/analog conversion chip. Only one CPLD is used to drive the LCD. CPLD adopts Altera's MAX3000 series. This part is used as an auxiliary function and can be selected according to the actual application.
The Ethernet controller (ie EMAC) of the DM642 belongs to the data link layer, so an external physical layer chip is required for network communication. Here, Intel's LXT971A chip is provided, which provides a MII (Media Independent Interface) interface, which can be easily and DM642 connection.
The power management part plays a pivotal role in the design of a hardware system. The power module of this system uses MAXIM's solution, including a MAX1762 chip (which generates 1.4V power to the I/O of the DM642 and generates 5V power to the LCD. Transformer power supply).
2 device driver design
TI developed a two-layer device driver model for the VP port of the DM642. The upper driver is called the Class Driver, which is closer to the underlying hardware. The application only needs to write the driver according to this model.
For Ethernet ports, TI provides a Network Development Kit (NDK) that provides a platform for developing web applications on DSP. With this platform, you don't have to think about how data is encapsulated into IP when developing web applications. Packages, do not care too much about the internal working mechanism of the TCP / IP protocol, which can shorten the product development cycle and time to market.
1.2 Two-layer device driver model for video port
The two-layer device driver model is shown in Figure 2. The top layer is the application, and the bottom layer is the underlying hardware, including the VP port of the DM642 and the video A/D chip. The middle of the large curly braces is the device driver. There is a chip support library (CSL) that provides a C language interface for configuring and controlling on-chip peripherals.
According to the characteristics of the VP port, each layer of the device-driven two-layer driver model is subdivided into two layers. As can be seen from Figure 2, the Class Driver is divided into FVID Class Driver and GIO Class Driver. The former is closer to the application. It provides some API functions that are especially suitable for images; the latter provides API functions for communicating with the Mini Driver. The Mini Driver is divided into general parts and special parts. The advantage of this is that when changing the hardware configuration, there is no need to rewrite the Mini Driver. Just modify the special part to improve the reusability of the code.
2.2 Network Development Components
The core of the network development component is a series of TCP/IP protocol stack libraries. It includes: (1) stack library and network tool library, which contains some optimized compiled protocol stack code; (2) operating system adaptation library, which is used Coordinating the interface between the TCP/IP protocol stack and DSP/BIOS; (3) Network control and scheduling library, which determines the initialization of the TCP/IP environment and how network-related events are scheduled; (4) Multiple hardware abstraction layers The platform library provides support for TI's various development boards (such as DSK, TEB, and EVM). Since this system is self-developed, it does not involve HAL.
The flow diagram of the protocol stack library is shown in Figure 3. The gray modules represent the top five libraries.
3 software design and implementation
TI's DSP development software includes Integrated Development Environment (CCS), real-time operating system (DSP/BIOS), and third-party algorithm library standard (eXpressDSP). DSP/BIOS is a user-croppable real-time operating system that includes memory management and threads. Management, interrupt, peripheral management and task scheduling. In addition, you need to use the JPEG standard for image compression, because when using JPEG for network transmission, if there is a short network block, the current frame can be discarded without affecting the next frame. Image, so it can guarantee the real-time requirements of the system. In this system, the JPEG algorithm library provided by TI is called to complete JPEG compression.
3.1 software process structure
According to the requirements of the system, the whole software system is divided into five task modules, each of which completes the function of steady and declining. The five task modules are input task, processing task, output task, network task and control task, respectively. The process is shown in Figure 4. The following describes the inter-task scheduling and separately completed functions.
(1) Input task
The task module mainly completes storing the digital image collected by the VP port into the dynamically allocated memory space, and the image format is YUV4:2:2 (can be set as needed), the resolution is 720×480. Then the image color The degree signal is resampled at 4:2:0. The purpose of this is to call the JPEG algorithm library. After completing the above two steps, the input task module sends a message to the processing task module to inform the image of the location in the memory space for processing. The task module performs further processing. Then, the input task module waits for the processing task module to reply, and after receiving the reply message, continues to acquire the next frame image.
(2) Processing task module
The task module mainly completes JPEG compression. The processing task module first obtains a message sent from the input task module and obtains image data therefrom. Then, JPEG compression is performed. As described above, the compression calls the JPEG algorithm library, and the compression speed and The performance is better. After the processing task module completes the image compression, three messages are sent: the first one is sent to the input task module, so that it continues to acquire the next frame image; the second is sent to the network task module, and the JPEG image is in the memory. The location and the number of bytes tell the network task module for processing. At the same time, the processing task module will wait for the network task module to reply to the message; the last message is sent to the output task module to inform the original image in the memory, and let the output task module Output it to the LCD for display. Similarly, it will also wait for the output task module to reply to the message.
(3) Output task module
The task module completes the acquisition of the original image output LCD for display. Since the YUV image is acquired, and the LCD of the system uses the RGB signal as the input, this needs to be converted by the digital image format, and the conversion is performed by the CPLD.
(4) Network task module
The task module completes the network transmission function. It is implemented in three parts: the first part first obtains a message sent from the processing damage module, obtains the size of the JPEG image and the position in the memory, and uses the Socket socket of the UDP protocol to Send to the client. Simultaneously send a message to the processing task module, indicating that the JPEG image has been obtained, and the next frame image can be compressed. The second part is to initialize the protocol stack, including the IP address, subnet mask and gateway settings. If you want to connect to the Internet, you must set up DHCP to dynamically assign an IP address. In addition, you need to choose which network service, DM642 supports Telnet, HTTP, Data server and other services, the system uses HTTP service. The third part is to load the webpage. Write a web page in HTML on a PC, embed a Java Applet applet in the web page to realize the interaction between the system and the client. The HTML file cannot be directly loaded to the DM642, and must be converted to C in the DOS environment using the binsrc plugin. The data array of the language description. When the user accesses the system through the IE browser, the HTTP server accesses the HTML page in the memory through the embedded file system (ie, accesses
(5) Control task module
The task module completes the control of the JPEG compression performance on the HTML webpage. The user-defined parameters received in the webpage are transmitted to the processing task module through the mailbox mechanism in the DSP/BIOS, thereby modifying the compression parameters of the JPEG and changing the compression. Quality. Figure 5 shows the dialog box for receiving user-modified parameters. 1 indicates the worst compression quality and 100 indicates the best compression quality.
The initialization of these tasks is implemented in the main() function of the system. In addition, the initialization of the DM642 chip (including the initialization register, the level 2 cache (L2) settings, etc.) is done in the dm642init() function, which is defined in the DSP. /BIOS user initialization function list, no longer repeat here.
The design scheme of the network camera based on TMS320DM642 proposed in this paper has been successfully implemented. Open the IE browser on the client, you can see the real-time monitoring image, the image display is smooth, and the image frame rate in the LAN can reach 30 frames/second. Moreover, multiple video signals can be collected at the same time to meet the connection request of multiple customers. The system satisfies the requirements of network video conferencing and video monitoring in the current broadband environment, and its application prospect is very extensive.
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