In-vehicle infotainment systems have played an important role in improving the comfort of car rides, which has led to the rapid development of car entertainment systems in recent years. On the one hand, users' requirements for multimedia entertainment are gradually increasing; on the other hand, due to the continuous development of automotive electronic hardware and software technology, various automotive entertainment system applications are also possible. The technological development of in-vehicle entertainment systems is becoming increasingly complex, and simple audio systems that transmit audio data over copper cables have become a thing of the past. In order to meet the requirements of multi-channel audio processing and distributed video, complex network processing has become more and more popular. In particular, Media Oriented System Transport (MOST) optical networks associated with digital transmission content protection (DTCP) encryption and decryption methods are being adopted by many high-end and mid-range vehicles.
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1 system composition
The system uses Freescale's IMX35 processor, which is based on ARM11TM core technology, designed for high performance, low power, data connectivity and multimedia to meet the needs of today's multimedia applications. The system is connected to a mobile phone with Bluetooth function through Bluetooth to realize hands-free calling, and can play audio files of various formats inserted in the U disk of the system, and the vehicle GPS provides navigation information for the driver. Connect the car amplifier and DVD player through the MOST bus to transmit audio, video and control commands. The structure of the infotainment module is shown in Figure 1.
1.1 Power Management
Power management in the car is a challenging task. The car's power source is a battery with limited power. After the car is turned off, on the one hand, the in-vehicle system, especially the infotainment system, cannot have excessive power consumption, and it must be ensured that the normal battery can still be ignited smoothly after several days or even weeks; on the other hand, the infotainment system To be able to respond effectively and timely to specific events in an ultra-low power state. The solution is to customize the multi-level standby state according to specific needs, so that the infotainment system can gradually enter the low-power standby state as time goes by and the battery power drops until it is completely shut down. The IMX35 processor has different levels of power mode, standby mode, sleep mode, stop mode, and still mode. The power consumption of each mode is gradually reduced.
1.2 Audio Processing Section
The audio system is divided into three parts. The first part is the USB part. In this part, the IMX35 reads out the audio file in the USB drive, selects the playback mode according to the settings, and transmits the audio information to the MOST via the speaker or through the earphone; The second part is the Bluetooth part. The Bluetooth system transmits the received voice information to the IMX35, and then selects the play mode according to the settings. In the third part of the MIC part, the IMX35 transmits the CODEC-processed audio information collected by the MIC to the Bluetooth coded. Sended to the mobile phone, the mobile phone sends the voice information to the other party's mobile phone through the wireless network. The first part and the third part are mainly digital, that is, the PCM encoded stream is transmitted through the serial port or the USB port. The second part consists of two parts: analog and digital. Firstly, the voice information collected by the MIC is processed by the op amp, then sampled by the CODEC and sent to the IMX35. For the headphone output, the PCM encoded stream transmitted by the IMX35 is converted by the CODEC into D/A conversion, and converted into an analog signal and sent to the earphone. Therefore, there are two main tasks of the CODEC. One is to convert the sound waves recorded by the outside world from analog signals to digital signals for processing by the IMX35 system. The analog signals recorded from Mic In or Line In must pass this program. In order to make the IMX35 understandable, the other is the reverse process work, that is, the digital audio data of the IMX35 is restored to the analog sound through the CODEC. It can be seen that the role played by the CODEC in the components of the audio system is quite critical.
1.3 GPS section
GPS vehicle application is a hot spot in GPS applications in recent years. More and more consumers add GPS functions to the car to facilitate travel. In this system, the IMX35 sends the received GPS information to the DVD player for display, and sends the geographical location information to the power amplifier for voice playback through the MOST bus. Since the GPS system receives weak signals from distant space, the requirements for system design and component receiving sensitivity are very high. However, due to the special application environment, the car GPS needs to pay more attention to the design. To solve these problems, in addition to ensuring that the chipset receives high quality signals, it is also important to increase the sensitivity of the receiver. This system uses the GPS chip LEA-4A of UBLOX.
1.4 MOST communication
The MOST bus is increasingly being used in systems such as car audio and video. The MOST bus not only has a fast transfer rate, but also has the advantages of reduced attenuation, light weight, and strong resistance to electromagnetic interference. The MOST bus is specifically designed to meet the demanding vehicle environment. This new fiber-based network is capable of supporting data rates of 24.8 Mb/s and is lightweight and resistant to electromagnetic interference (EMI) compared to previous copper cables. The MOST bus is based on a ring topology network with up to 64 masters on a single network.
The MOST transmission protocol consists of data blocks that are divided into frames, each frame containing stream data, packet data, and control data. Stream data is synchronized with the MOST clock and is continuously cyclically transmitted across the network. The packet data is asynchronous to the MOST clock and is generated as needed. The bandwidth allocated between the stream data and the packet data in the frame is variable to meet the system's needs at a particular time, and its control words contain stream information such as data type, where data can be found in the frame, and data size. Control information can be allocated in multiple frames and should be reconstructed in the receiving device.
In this system, two OSTA control chip OS8104s from OASIS are used. The data transmission of MOST in the system is controlled by IMX35. The control information transmission between IMX35 and the first OS8104 is realized by SPI bus. The processed digital PCM audio stream is transmitted through the serial port. The data information transmission between the IMX35 and the second OS8104 is realized by an 8-bit parallel port bus, which is used to transmit control information and some asynchronous data in the MOST network. The two MOST chips are connected via TX and RX via a resistor R422, forming a loop inside the module. It is then connected to the FOT interface, which converts the received optical signal into an electrical signal, and also converts the electrical signal to be transmitted into an optical signal.
1.5 Bluetooth section
The Bluetooth system uses CSR BC41B143. The chip integrates the Bluetooth 2.0+EDR Bluetooth version. The 2.0 version of the Bluetooth standard is a modified version of version 1.2 with a transfer rate of approximately 1.8 Mb/s to 2.1 Mb/s and can work in duplex mode. For voice communication, files and high-quality images can also be transmitted. The IMX35 communicates with the BC41B143 via a USB interface to deliver voice messages.
The design of the Bluetooth antenna is the most important part of the Bluetooth system hardware design. It is related to the bandwidth and quality of the received signal, which affects the communication quality. At the same time, the cost is also a consideration. In this system, the F-shaped PCB trace is selected to make a Bluetooth antenna, which saves a lot of cost compared with the purchase of the finished Bluetooth antenna. There should be no metal parts in the range around the antenna to avoid interference with transmission and reception. After the product is completed, the communication results show that the signal quality is good, the communication state is stable, and the bit error rate is very low.
2 software components
The in-vehicle infotainment system is a multi-tasking complex system that contains many subsystems that interact with the car network. The system software is designed with real-time characteristics in mind. On the one hand, the introduction of real-time design can bring users a better application experience, such as stable and smooth multimedia playback, accurate and effective navigation tips, etc. On the other hand, the system's real-time design can guarantee certain mission-critical tasks. Smooth execution, such as Bluetooth phones.
The software of the system adopts a modular design. A good software module can ensure that failures in one module will not cause other modules to fail, and will not cause the entire system to fail; the failed module will be restarted quickly, and at the same time The rest of the system is functioning properly. At the same time, the fault code is generated and recorded, so that the system can provide sufficient information to the diagnostic personnel during the system diagnosis, which has a great effect on improving the defects of the product and improving the quality of the product.
This system module adopts Windows CE 6.0 operating system. The change of CE 6.0 in the kernel is mainly to meet the requirements of embedded device hardware development. In terms of the number of processes, it has changed from running up to 32 processes in the past to up to 32 000. Process; memory, from each process up to 32 MB of virtual memory space to up to 2 GB of virtual memory space; in terms of OS layout, the key driver, file system and graphical interface manager (GWES) moved to the kernel In the case, the performance loss caused by the CPU switching between the kernel state and the user mode can be better solved.
The IMX35 is a processor specially designed for in-vehicle multimedia applications. It can adapt to complex electromagnetic environments and is equipped with a variety of peripherals to form a stable and reliable infotainment system. The product can run stably and reliably for a long time.
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