1 Introduction
The compressed audio format is widely used by PCs and audio systems all over the world. In order to deal with this type of digital audio signal, Renesas Technology has launched the SH7263 high-performance microcontroller integrated with the SH2A-FPU core. The maximum operating frequency of this LSI is 200MHz, which integrates single-precision and double-precision calculation support FPU, which achieves high-speed signal processing capabilities.
The SH7263 has an on-chip CD-ROM decoder and sample rate converter, and is especially suitable for digital audio systems, such as car audio and home audio with audio encoding and decoding functions.
In addition, this LSI also integrates a host and function interface that meets the requirements of the USB standard v2.0 high-speed (480 Mbps) and a display controller that supports an LCD panel with a size of WVGA (800 × 480 pixels). These features provide display system functions and enable a low-cost configuration of a digital audio player that performs high-speed data transmission by connecting a USB flash memory or portable audio or similar USB device.
And, this LSI also has peripheral functions such as CAN controller, IEBus controller, serial sound interface (SSI) for digital audio data input / output, serial communication interface, and a 16-level FIFO and 1 I2C bus interface.
Figure 1 SH7263 evaluation board and car audio head unit
2 System block diagram
Figure 2 SH7263 digital car audio system block diagram
The system block diagram of the entire digital car audio system is shown in Figure 2. There is a 16-bit MCU responsible for system control functions, and SH7263 acts as a slave device to receive commands on the system MCU via UART. Not only the CD panel, but three main storage devices (SD, USB and NAND Flash) are attached to the SH7263. With the help of middleware, CD-DA 16-bit PCM format code can be compiled into MP3 / AAC format code and stored in SD, USB or NAND Flash memory. The maximum speed of the capture process is about 4 times that of AAC format and 3.2 times that of MP3 format. At the same time, MP3 / AAC / WMA decoder middleware is also provided to decode this format and output it to the power amplifier.
3 Software structure of SH7263
The software structure of SH7263 is shown in Figure 3, and the entire software runs under uITRON OS 4.0. In addition to uITRON OS, it can be divided into 3 layers: user API, framework layer and driver layer. In the framework or middleware layer, it can be divided into codec framework, IOIF framework and file system framework, and each framework has its specific function. The codec framework is mainly responsible for audio encoding and decoding. The IOIF framework is used to simulate the POSIX API interface of the user API and control the hardware through the driver layer. File systems such as FAT and ISO9660 can be processed using the file system framework.
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