Design and Implementation of MPEG-4 Digital Video Recorder Based on S3C2410

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[Abstract] This paper introduces a digital video recorder based on embedded microprocessor S3C2410 and MPEG-4 dedicated video compression chip IME6400 and large-capacity electronic hard disk. The overall design of the system is discussed. The design of each functional module and key interface circuit is introduced. The design and implementation of the driver and application under Linux are introduced.
[Keywords] S3C2410 IME6400 MPEG-4 Linux device driver

Video information plays an increasingly important role in modern information warfare. It has been widely used in video surveillance, reconnaissance, airborne or vehicle video recording. This situation has brought new developments to digital video surveillance recording equipment. Requirements: High-volume applications require lower monitoring and recording equipment costs. Diverse application environments, decentralized, isolated monitoring points require monitoring and recording equipment to be as integrated, compact, independent, portable, low-power, convenient, and reliable. . In response to these new problems and new requirements, the author designed and implemented a digital video recorder based on embedded system and MPEG-4 encoding standard. The system has high integration, small size, low power consumption, independent and portable, suitable for a large variety of video. Monitor and record applications.

1 system overall design and principle

figure 1

The system selects the embedded microprocessor plus special compression coding chip scheme. The main circuit block diagram of the system circuit is shown in Figure 1. It mainly consists of video and audio decoding chip, video and audio compression coding chip, core microprocessor control module, power module and various External interface and so on. The system is powered by a single 5V power supply. After normal startup, the video and audio decoding chips SAA7114 and PCM1800 decode the input analog video and audio signals respectively, and send them to the compression coding chip IME6400 for compression to generate MPEG-4 composite stream. The chip S3C2410 receives data from the HOST interface of the IME6400 and stores it in the form of a file to the hard disk and completes the overall control of the system.

2 hardware design

2.1 Video and audio decoding and compression coding part design

The video A/D chip uses Philips' SAA7114, which supports multiple input modes, with anti-aliasing filtering, automatic gain conversion, brightness, contrast adjustment and other functions. A seamless connection to the IME6400 is achieved by setting the internal configuration register 93H[6] of the SAA7114 to 1 to enable its HOST port. The audio A/D chip uses BURR-BROWN's PCM1800, which performs high-signal-to-noise ratio 20-bit digital sampling on analog audio to generate a PCM digital audio stream.

Compression coding uses the MPEG-4 encoding chip IME6400 from INTIME. The chip is a high-performance single-chip multi-channel MPEG-4 digital compression encoding chip that supports multiple encoding modes and bit rate control, and provides a rich peripheral hardware interface. Its external HOST interface has four modes, which are determined by the MODE pin. The system uses asynchronous mode: MODE[1:0] pin = 11. In this mode, the IME6400 compresses and combines the input video and audio streams to produce an MPEG-4 system stream, and then outputs the data through a FIFO buffer with an output port size of 1K. When the FIFO is full, its GPIO0 pin generates a data. The interrupt on the falling edge informs the host to read the data in the FIFO. The host reads the data in the EncodedStream register of the IME6400 HOST port through 512 times (16bit host). The external host notifies the IME6400 data transmission by writing a different value to the USER4 register. Completed ^[1] .

2.2 control, interface and storage part design

The system control module uses Samsung's S3C2410 microprocessor, which is a high-performance, low-power, low-cost 32-bit microprocessor using the ARM920T core ^[2] . In order to improve the flexibility of design and application, the hardware design adopts the modular design method of core board and backplane, and the minimum system based on S3C2410 is integrated on the core board, and the external function is extended through the backplane. The core board is mainly equipped with 64MB of NANDFlash and 64MB of SDRAM and a crystal that provides RTC clock and working clock, and draws out its rich peripheral interface resources. The USB host interface, Ethernet port, UART interface, IDE interface, etc. are extended on the backplane to implement data transmission and communication with external devices.

The S3C2410 does not have an IDE control module. The interface circuit needs to be designed separately. Figure 2 is a schematic diagram of the IDE interface circuit. The circuit uses the chip select signal nGCS4 of the fifth BANK of S3C2410 and the address signals ADD4 and ADD5 to form two chip select signals nIDE_CS0 and nIDE_CS1 of the IDE interface. The read and write signals nOE and nWE of S3C2410 are directly used for reading on the IDE interface. Write signals nIOR, nIOW. This method maps the IDE interface to the fifth Memory Bank of the S3C2410. The S3C2410 treats the IDE device as normal memory and accesses it in the same way, which greatly reduces the complexity of system software development ^[3] .

The HOST interface of the IME6400 is mapped to the sixth Memory Bank of the processor in a manner similar to the IDE interface. The system storage part uses an electronic hard disk with small volume, good shock resistance and wide temperature range as a memory.

3 software design

Because the Linux system has the advantages of stability, high efficiency, easy customization, easy to cut, open source, etc., the system uses embedded Linux as the operating system, and realizes IME6400 driver design and related application program design under this system.

Linux treats the device as a file. The main job of writing a Linux driver is the implementation of each entry point in the file_operations structure, which corresponds to the open(), release(), read(), write(), ioctrl(), etc. Call the subfunction to write ^[4] . At the same time, the device driver of the system adopts a dynamic loading method with better flexibility, and the driver should also include a module initialization function and a module logout function. Here are a few of the main functions and their functions:

The module initialization function is called when the driver is loaded, mainly to complete the following functions:

Apply to mount the actual physical address space of the video encoding chip on the bus and map it to the virtual address space:

Request_region(BASE_ADDR, 0x100, "IME6400")

Vbase = ioremap_nocache(BASE_ADDR, 0x100)

Register the device and get the major device number ^[4] :

Ret=register_chrdev(IME6400_MAJOR,"ime6400",&ime6400_fops)

Set up and apply for interrupt and register interrupt handlers:

Set_external_irq(IRQ_EINT19, EXT_FALLING_EDGE, GPIO_PULLUP_DIS) request_irq(IRQ_EINT19, &ime6400_irq, SA_INTERRUPT,"ime6400", NULL)

Register device file system:

Ime6400_devfs_dir= devfs_register(NULL,"ime6400",DEVFS_FL_DEFAULT,IME6400_MAJOR,0, S_IFCHR |S_IRUSR |S_IWUSR |S_IRGRP |S_IWGRP,&ime6400_fops, NULL)

The OPEN function increments the module usage count to prevent the module from being unloaded without releasing the device.

The READ function blocks waiting for the data buffer to be full and then copies the data from kernel space to user space.

l The IOCTRL function implements parameters from the user space to the kernel space for setting the IME6400 working mode.

l The interrupt handler reads the MPEG-4 stream data output from the IME6400 and stores it in the kernel buffer and notifies the IME6400 that the data has been read. Linux divides the interrupt handler into two parts: the top half is the routine that actually responds to the interrupt, and the bottom half is a routine that is called by the top half to run in a safe time later. ^[5] . Linux uses the Tasklet mechanism to implement the bottom half processing, and the macro DECLARE_TASKLET can declare the Tasklet:

Static DECLARE_TASKLET(ime_tasklet, do_tasklet, NULL), where the do_tasklet function actually handles interrupts, reading data from the IME6400 to the kernel buffer. A tasklet can be scheduled to run via the tasktalet_schedule(): tasklet_schedule(&ime_tasklet).

The system application mainly realizes receiving MPEG-4 code stream data from the driver layer and storing it to the hard disk, mainly adopting multi-thread programming mode. The main program creates two threads of read and write threads: First, the user program read thread calls read ( ), at this time the encoding has not yet started, the driver is ime6400_read() without data readable, enters the sleep state, and the user process is blocked. After the interrupt arrives, the interrupt handler reads the data from the IME6400 and stores it in the kernel buffer. If the buffer is full, wake up the ime6400_read() and write a new value to the USER4 register of the IME6400 to notify the IME6400 that the data has been read. Start a new round of coding. After ime6400_read() wakes up, it copies the kernel buffer data to the user buffer, then returns and waits for the next call from the user process. After ime6400_read() returns, the user space reads the encoded data to exit the blocking state, and then the reading thread notifies the writing thread by the semaphore, and the writing thread finishes storing the buffer data to the hard disk.

4 Conclusion

The system has completed initial debugging, and can compress and store 4:2:2 color video with a maximum resolution of 720x576 full frame rate in real time. It can record more than 2 hours at 720x576 resolution with 2G electronic hard disk, and the image quality better. At the same time, the system also has better flexibility. By setting parameters such as video image resolution, quantization coefficient and frame rate, different requirements for image size, image quality and code rate can be achieved to meet the application of different occasions. need.

The author of this paper innovates: Design and implement MPEG-4 compression record based on ARM and embedded Linux platform, realize system integration, miniaturization, high performance, low power consumption, adopt core board and bottom board in hardware design. The modular design method completes the development of the driver under the Linux system on the software.

references:

[1] IME6400 firmware manual. Intime Corporation. 2003
[2] S3C2410X 32-BIT RISC MICROPROCESSOR USER'S MANUAL. Samsung Electronics.2001
[3] Meng Ke Li Fengting Ma Huimin, portable digital video recorder design for video surveillance, TV technology, 2002.7
[4] Qian Chen Xu Ronghua Wang Qinruo, device driver development based on linux operating system, microcomputer information, 2004.09, 131-133
[5] Wei Yongming, Yu Yuezhong, translation, Linux device driver (third edition), China Electric Power Press, 2006.1

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