Abstract: Based on the control and computing capabilities of the ET44M210 microcontroller chip, the multimedia functions of the ET83X431 audio processing module and the ET52141 OLED image display module, a portable embedded multimedia tour guide system is realized by utilizing the USB interface between the device and the PC to complete communication and audio/video download transmission. Keywords: ET series chip, USB communication, multimedia playback, tour guide function, embedded system. With the development of microelectronics technology and VLSI, embedded microcontroller technology has become increasingly mature. Embedded technology not only performs well in industrial applications such as industrial control systems, intelligent instruments, detection systems, and measurement and control units, but is also increasingly being applied to various consumer electronics products. The embedded multimedia tour guide system introduced in this paper is based on the control and computing capabilities of the ET44M210 microcontroller chip, the multimedia functions of the ET83X431 audio processing module and the ET52141 OLED image display module. It utilizes the USB interface between the device and the PC to complete communication and audio/video download transmission, combined with a keyboard input human-machine interface, integrates the interfaces of various hardware modules, fully leverages the advantages of each component, achieves the design goal of auxiliary tour guide function, and expands its application in the field of multimedia digital technology. 1 System Overall Hardware Design 1.1 System Hardware Structure and Principle The embedded multimedia tour guide system based on the ET series chip consists of a regular PC, an embedded microcontroller (MCU), an audio processing module, an OLED display module, a Flash storage unit, and a keyboard control unit. Its hardware structure is shown in Figure 1. The host computer program on the PC is responsible for communication applications via the USB interface and the conversion and processing of raw audio and video data. The MCU responds to commands input in real-time by the keyboard control unit, completing USB interactive communication with the host computer program on the PC or large-scale downloading and transmission of audio and video files from the PC. The device stores the loaded audio and video files in the Flash storage unit, and the keyboard commands control the MCU to complete the transmission of audio and video data to the audio processing module and the OLED display module. The audio processing module and the OLED display module process and play the audio and video data in real time, thereby completing a comprehensive description of each tourist attraction. Simultaneously, the audio processing module, driven by the MCU, can also record and play analog audio in real time. 1.2 ETUSBICE Embedded Microcontroller Development Component ETUSBICE is a dedicated ICE component and development environment for the ET44M210. The ET44M210 is a high-speed CMOS MCU with a USB+BB microcontroller and an 8-bit RISC architecture. In addition to microcontroller functions, it provides a baseband (BB) for 2.4GHz wireless transmission, a USB hub, a serial peripheral interface (SPI), dual pulse width modulation (PWM), and 16 multi-channel 10-bit analog-to-digital converters (ADCs). These powerful features broaden the application range of the ET44M210 and provide greater design flexibility. 1.3 Audio Processing Subsystem This subsystem utilizes the ET83X431 module to implement audio file recording and playback functions. The ET83X431 is the main chip of this system module, packaged in a 48-pin package, and includes two 16-bit ADCs, two 16-bit DACs, a continuous audio interface, digital filtering devices, compression/decompression modules, and other functions, providing high-quality stereo audio compression and decompression capabilities. The ET83X431 chip, in conjunction with its overall module hardware architecture, can directly decode and play audio files of special formats. Therefore, a PC-side host computer program needs to be designed to convert the audio samples from the desired audio files (such as mp3, wma, wav, etc.) or video files (such as avi, wmv, mpeg, etc.) into an audio format common to this module. The converted audio file is then downloaded to the device via USB and, under the overall coordination of the lower-level system, the subsystem enables direct playback of the audio stream file. Simultaneously, this subsystem supports direct analog sampling. The ADC and DAC sections of the subsystem can convert between analog and digital audio signals, and the ET83X431 can directly sample and compress analog audio signals. 1.4 OLED Display Subsystem Organic Light-Emitting Diode (OLED) displays refer to a technology that uses organic semiconductor materials and light-emitting materials to emit light under current drive to achieve display. The ET52141 color OLED controller and driver module supports 96×96-dot 65k-color display, featuring convenient bit manipulation capabilities, a 16-bit high-speed bus interface, efficient data transmission capabilities, and high-speed writing capabilities to the graphics RAM, making it suitable for terminal designs such as digital mobile phones or small PDA devices. The OLED display subsystem primarily relies on the precise coordination of the PC host computer, device-side microprocessor, Flash unit, RAM unit, and ET52141 module to achieve its design functions. Based on a thorough understanding of bitmap and audio/video file formats, the entire design process requires the rational configuration of various hardware resources and the coordination of timing to achieve the display of static images, the creation of system menus, and the continuous playback of animated images. 1.5 USB Communication between PC and Embedded Microcontroller The design goal of this USB communication subsystem is to achieve data interaction and data transmission with the PC and USB devices via the USB interface and USB protocol. For example, this interface can be used to download images or audio information, audio/video data, read information from the Flash unit, and upload it. The firmware on the USB device side works in conjunction with the host computer program to coordinate USB data transmission. 2 System Software Design The embedded multimedia tour guide system software based on the ET series chip consists of a host computer program and a slave computer program. The host computer program is mainly written using Borland C++Builder 6, while the slave computer (embedded microcontroller MCU) control program is written using Borland C++Builder 6. The overall architecture of the host computer and slave computer software is shown in Figure 2. 2.1 Host Computer Program The PC-side host computer program consists of three parts: USB communication application, audio/video data processing, and USB driver. The first two parts are written using Borland C++Builder 6. The USB communication application is located above the PC-side USB driver and strictly follows the four USB communication modes (Control, Interrupt, Bulk, Insochronous) to cooperate with the slave computer to complete USB communication and bidirectional data transmission. The user interface buttons are mostly used for USB device responses in interrupt mode, cooperating with multiple interrupt addresses and vectors of the slave computer to change the USB device state and complete the transmission of control commands. The Bulk mode is specifically designed for continuous transmission of large amounts of data, using 64-byte frames with a transmission interval of less than 1ms. This part of the program requires defining the GUID of the USB device to connect to it via the USB driver and utilizing Windows API functions to obtain the USB device's handle. This software implements multiple loops for bulk transmission, with the host computer coordinating with the slave computer's input/output FIFOs and RAM buffers to complete upload or download operations, achieving resource sharing between the PC's storage and the slave computer's Flash storage. The audio-visual data processing section trims and converts the audio-visual resources stored on the PC according to the user's intended use, creating audio-visual files that can be directly read and played by the slave computer's ET83X431 and ET52141 modules, ultimately achieving the goal of using video materials or scenic spot introductions to assist tour guides. For example, for AVI format audio-visual data, this software decodes and samples it into bitmap information and audio data, and encodes and integrates and converts the files according to the specific needs of the slave computer firmware. The generated audio and video files can be mass-transmitted to the lower-level Flash unit via USB communication for storage and playback by various modules. 2.2 Embedded Microcontroller (MCU) Program ETUSBICE is a dedicated ICE integrated development environment (IDE) for the 8-bit processor ET44M210, featuring an editor, project window, assembler, debugger, etc. The firmware program for the embedded microcontroller is written and edited using this IDE. This embedded microcontroller (MCU) program is broadly divided into three parts: system operation part, multimedia module function parts, and USB communication service part. The structural relationship of the three parts is shown in Figure 3. The system operation part is the main program that runs independently of the entire system. From system power-on to system shutdown, the program runs in this part of the software flow. This part of the software integrates the resources of various modules of the system, coordinates various hardware modules, monitors other software modules, and rationally allocates various registers, RAM resources, Flash resources, and I/O resources. It receives keyboard input commands and USB input commands in real time, accesses various subsystem modules in real time according to the current task requirements, precisely manages each process step and maintains the display menu, and coordinates various resources to maintain mass transmission communication. During system operation, if a keyboard command is received requiring the audio subsystem or OLED display subsystem to be run, the various unit functions in the multimedia module's function functions can be called to complete the keyboard response, produce multimedia effects, and ultimately return the process to the main program. The program for the system operation portion is shown in Figure 4. The USB communication service program directly responds to the host computer's USB communication application program via the protocol, serving as the embodiment of the latter's control commands on the device side. This part of the program typically runs in the background of the software flow, providing a powerful supplement to the system operation portion. This part of the program includes the USB program library and macro set, serving as the main body for device-side USB control in response to the host computer's control (Contr01) information. It is also called by upper-level functions in the firmware to complete low-level settings and operations such as device-side USB initialization and SOF counter. When responding to host computer commands, if the audio subsystem or OLED display subsystem needs to be run, the functions in the macro set can call the various unit functions in the multimedia module's function functions to complete the response to the host computer commands and produce multimedia effects. Multimedia module function sets are collections of application function modules written based on the characteristics of hardware resources such as the audio processing subsystem, OLED display subsystem, RAM unit, and Flash unit, with the aim of implementing specific multimedia functions. This collection stems from a deep understanding of the characteristics of each hardware module, full utilization and exploitation of hardware resources, strict control of timing, precise software flow, reasonable allocation of storage resources, and coordination of MCU processing capabilities. This results in a set of functions corresponding to each multimedia requirement, such as audio playback, still image display, video playback, and audio recording. Each function set includes a convenient application programming interface (API) to facilitate the main program calling this function. The embedded multimedia tour guide system based on the ET series chip uses high-performance, reasonably priced hardware modules, features a user-friendly interface, excellent performance, and a high performance-price ratio. As a novel consumer electronics solution, it has a unique concept and promising application prospects.