Design of wireless multimedia playback system based on S3C2440A processor and wireless transceiver module

Based on embedded Linux technology, a design scheme of an intelligent wireless multimedia digital playback system is proposed. The system functions, overall structure, main control CPU and wireless module are introduced. Through the control of the wireless module driven by the SPI interface in the Linux system, automatic identification of regional locations, controlled playback of audio and video files, and a graphical interface operating program for interaction with users have been successfully realized.

1. System composition

The structure of an embedded intelligent wireless multimedia playback system that can automatically receive and identify wireless address codes is shown in Figure 1. The system consists of a handheld intelligent wireless multimedia terminal and an address code wireless transmitter.

Address code wireless transmitters are installed at various attractions or booths to periodically transmit their own address codes. Different attractions/booths have different address codes. The same attraction/booth can be equipped with one or more transmitters with the same address code. , try to make the transmitted signal cover the entire attraction/booth, and at the same time avoid cross-interference between adjacent attractions/booths through transmission power control technology. As the user moves, the handheld smart wireless multimedia terminal he carries will automatically receive the address code corresponding to the attraction/booth when approaching an attraction/booth. By parsing the address code, the receiving terminal calls and switches to the The audio and video files pre-stored in the SD memory card corresponding to the address code are played. The user can watch the playback content through the LCD touch screen, or terminate the automatic playback and manually select other audio and video files for playback.

2. System design

2.1 System design indicators

The design indicators are: the coverage area of ​​each attraction/booth is adjustable from 5 m to 25 m; each attraction/booth does not interfere with each other; the attraction identification code transmission uses the ISM frequency band; the signal transmission power is adjustable within the allowable range; it can Works in a relatively harsh environment with temperature and humidity; uses an intelligent operating system to update applications at any time; automatically switches audio and video content at different attractions/booths; has a graphical user interface that allows users to manually select audio and video files and languages ​​through the touch screen; It can store audio and video files, the size and quantity are determined according to the capacity of the SD memory card, and can be downloaded and updated on-site; it supports the playback of audio MP3 and MPEG1-4 video files; the transmitting host complies with relevant national standards.

In order to meet the requirements of design technical indicators, the main components of the system are selected as follows: (1) The main control chip of the address code wireless transmitter is selected from TI Company's MSP430F133; (2) The main control chip of the handheld smart wireless multimedia terminal is selected from Samsung Company S3C2440A, the typical main frequency of this chip is 400 MHz, integrating NAND Flash controller, SD/MMC controller, LCD controller, SPI interface controller, etc.; (3) The wireless transceiver module uses CYWUSB6934; (4) The Flash memory uses Samsung The company's K9F1208UOB; (5) the SDRAM uses Hynix's HY57561620T; (6) the display screen uses NEC 3.5' TFT touch screen; (7) the audio decoding chip uses UDA1341TS.

The embedded operating system is composed of the following: (1) Bootloader uses the startup code VIVI specially developed by Samsung for its products; (2) The kernel uses Linux version 2.6.13 [3]; (3) The file system is better compatible with NAND Flash. YAFFS file system [4-6]; (4) The graphical user interface uses QTOPIA1.7 [7].

2.2 ARM9 embedded microprocessor S3C2440A

At present, the application of embedded technology is becoming more and more widespread. From aerospace technology to civilian products, embedded products are everywhere, and the core of these embedded products-the processor determines the market and performance of the product. In the 32-bit embedded processor market, ARM processors occupy a large share. Nowadays, due to storage space and other reasons, it is difficult to program on embedded chips, so it is very important to choose the appropriate platform. Linux has developed rapidly since its emergence. Linux is an open source operating system that attracts programmers from all over the world to participate in development and improvement work, so Linux maintains stable and excellent performance. Linux already occupies a large share in the server field, and it is not inferior to Windows in terms of graphical interface. Because the source code can be modified and transplanted, Linux is increasingly used in the embedded field.

S3C2440A is a processor designed by Samsung based on ARM920T, with a main frequency of 400 MHz; maximum expansion bus frequency of 100 MHz; 32 bit data, 27 bit external data line; completely static design (0~400 MHz); memory controller (8 memory banks), 4 16-bit timers with PWM; interrupt controller with up to 55 interrupt sources; RTC; 3 UARTs, support IrDA 1.0; 4 DMA channels support peripheral DMA; 8 channels, 500 kS/s, 10 bit ADC; supports STN and TFT LCD controller; watchdog; I2S audio interface; 2 USB interfaces; I2C-Bus interface; 2 serial peripheral interface circuits (SPI); SD card interface. Choosing the ARM9 chip can use the Linux operating system to reduce software development time, and the S3C2440A has good support for mainstream multimedia and is very suitable for developing intelligent multimedia systems.

2.3 CYWUSB6934 wireless transceiver module

The wireless transceiver module uses Cypress's CYWUSB6934. The chip can be used as both a transmitter and a receiver, operating in the 2.4 GHz ISM band with a frequency range of 2.4 GHz to 2.483 GHz. It has the characteristics of low power consumption and low radiation (the maximum radiation power is 0 dBm), and the transmit power is adjustable (a total of 7 levels); the wireless receiving sensitivity is high, up to -90 dBm; the communication radius can reach 10 m (when outputting The straight-line communication distance at maximum power and without obstacles can reach about 15 m). Due to its characteristics such as short distance and low power consumption, it is very suitable for short-distance wireless transmission.

2.4 Address code wireless transmitter

The address code wireless transmitter is a control system with a microcontroller as the core. It mainly includes a power module, a wireless transmission module and a transmission power adjustment toggle switch. The interface between the microcontroller and the wireless transmission module is an SPI port.

2.5 Handheld smart wireless multimedia terminal

The audio and video content of each attraction/booth is stored in the SD memory card in a specific format. Each file is named in a prescribed manner and corresponds to an address code.

After the handheld smart wireless multimedia terminal is turned on and completes hardware initialization, startup of the Linux operating system, mounting of the file system and startup of the graphical user interface, the user clicks on the smart on-demand system program icon on the graphical desktop to run the on-demand program. After the system queries this information, it immediately reads the data register of CYWUSB6934 to obtain the address code. The system will compare the received address code with the previous data. If they are the same, playback will continue. If they are different, the system will automatically switch to the file corresponding to the address code for playback.

3. Implementation of intelligent wireless on-demand

The microprocessor S3C2440A and the wireless chip CYWUSB6934 communicate through the SPI interface. In the Linux system, the communication between the two must be achieved through the SPI driver. Intelligent on-demand is when the user starts the on-demand program in the Linux system, and after the system recognizes the received data, it automatically calls the audio and video files for playback.

3.1 SPI driver

In the Linux operating system, the control of all peripheral devices is achieved through drivers. The device driver is the interface between the operating system kernel and the machine hardware.

SPI is the abbreviation of English Serial Peripheral interface. As the name suggests, it is the serial peripheral interface. It was first defined by Motorola on its MC68HCXX series of processors. The SPI interface is mainly used between EEPROM, FLASH, real-time clock, AD converter, digital signal processor and digital signal decoder. SPI is a high-speed, full-duplex, synchronous communication bus that only occupies four lines on the chip pins, saving chip pins and saving space in the PCB layout, providing convenience and correctness. Because of this simple and easy-to-use feature, more and more chips now integrate this communication protocol. Handheld smart wireless multimedia terminals need to control the wireless transceiver chip through the SPI interface, which requires the use of an SPI interface driver to establish a communication bridge between the wireless transceiver chip and the kernel. The SPI interface works in a master-slave mode, and its interface includes 4 types of signals: (1) MOSI: master device data output, slave device data input; (2) MISO: master device data input, slave device data output; (3) SCLK : Clock signal, generated by the master device; (4) /SS: Slave device enable signal, controlled by the master device.

Figure 2 is the connection diagram of the SPI interface between S3C2440A and CYWUSB6934. In the figure, nSS controls CYWUSB6934 as a slave device, SPIMOSI and SPIMISO are the data transmission channels between them, and SPICLK is the clock signal. When SPI serves as the master controller, it is controlled by the corresponding bit in the SPPRE register. When SPI is a slave device, the clock signal is provided by other devices. In some cases, nSS should be asserted high before writing data to the SPTDAT register. The SPI-related registers inside S3C2440A mainly used in this system are as follows: