In order to integrate different data buses, the gateway must provide bandwidth and response time.
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For electronic system design engineers, the automotive industry is entering an encouraging and challenging period, with applications such as infotainment, remote sensing testing, security and control requiring several networking standards. Design engineers face a number of tasks in order to select the right bus for the most demanding applications.
The automotive electronics market is no different from data communications, telecommunications and consumer electronics. There are many alternative networking protocols, each with its own advantages and disadvantages. A protocol is not possible to meet the needs of all automotive applications.
Car networks can usually be divided into three categories:
Body control: requires high bandwidth, high reliability and data integrity;
Infotainment: requires high bandwidth and real-time processing of audio and video;
Safety: Traditional hydraulics and sensors are being replaced by wire-driven driving and braking methods.
In order to store and process data from these networks, a gateway is required to interconnect the network and process data from the in-vehicle embedded network. A typical gateway consists of several automotive network interfaces (CAN, MOST, and Flexray) with embedded microcontrollers and peripheral functions.
CAN (Control Area Network) is particularly suitable for body control due to its low cost and high transmission reliability. A typical car contains several CAN network functions such as engine management, instrument control, and body control. Its maximum data rate is 1Mbps, so its bandwidth does not support the transmission of video and audio data. However, CAN is very cheap and fault-tolerant, and is therefore an important network protocol. According to ABI Research's "In-Vehicle Network Research Report" (fourth quarter of 2004), approximately 528 million automotive CAN nodes will be installed by 2010.
MOST (Multimedia Transport Protocol) meets the needs of video and audio functions, supporting synchronous and asynchronous data transmission at 24 Mbps on plastic fiber. MOST transceivers are required for devices such as DVD players, overhead players, GPS devices, and displays. The MOST Alliance has defined MOST interconnect standards and software application interface standards. MOST is a flexible and highly reliable network standard.
At present, the brakes and steering wheel are controlled by hydraulic mechanical methods. Future cars will replace hydraulic machinery, and FlexRay-based controllers will be used for wire control, including wire-controlled brakes and wire-controlled steering wheels. This wire-based network is fast and fault tolerant. FlexRay supports both synchronous and asynchronous data transfers at approximately 10 Mbps, ensuring stable data transmission, fault tolerance and response time to messages, and providing redundancy in dual channel mode.
Ethernet
In addition to the above-described in-vehicle network standards, a typical gateway includes several other interfaces. Ethernet is a widely used network standard for diagnostics and as a service interface. Its hardware costs are low and application software is available everywhere. Because this interface is used for diagnostics, it is not fault tolerant and noise resistant. To process data from CAN, MOST, and Flexray networks, an embedded processor is required. The processor splits, aggregates, and performs type conversion on the data. The Ethernet interface requires an embedded processor to run the TCPIP stack. Off-chip memory can store program code. In order to store temporary data from the embedded network, additional memory may need to be added.
Design factor
When a system design engineer designs a car gateway, many decisions may be required, including:
Which networks need to be bridged?
What bridge topology is used?
Need DMA (direct memory access)?
How big is the data buffer?
What bus is required for internal data exchange?
What should the bus width be?
What arbitration mechanism is needed?
How much processing power does it require?
The above questions depend on the system and application you are designing. However, there are also some common problems that must be dealt with. Obviously, CAN, MOST, and Flexray are different protocols. Their payload, data rate, and real-time processing requirements are different. The gateway must be able to efficiently process all incoming and outgoing data from these interfaces.
Using programmable logic devices to solve the bandwidth challenge faced by in-vehicle gateways
The general system bus must be chosen to carry the data within the gateway, which is typically a synchronous bus that operates at different frequencies in the automotive network. The system typically matches the clock frequency and bandwidth of the embedded processor, allowing data to be efficiently transferred between the processor and the network interface. The system bus line must meet the bandwidth requirements of all interfaces. The cumulative maximum bandwidth of each network protocol is a basic approximation.
For example, a network has four CAN nodes (4 Mb/s), one MOST (24 Mb/s), one FlexRay (10 Mb/s), and one Ethernet (100 Mb/s), resulting in a total bandwidth of 138 Mb/ s. It can consist of a 16-bit bus running at 10MHz. However, the total bandwidth does not meet all the requirements. Every system bus cycle has its purpose. The addressing and encoding cycles consume the available bandwidth. A target device such as a memory controller or network interface sometimes inserts a wait state when acquiring the necessary data. In both cases, you need to add extra bandwidth -- either increase speed or increase the width of the system bus.
Another important consideration is the payload and delay time. The CAN node transmits information in 8-bit data packets. Ethernet can transmit up to 1,500 bytes of data packets. There is overhead for every transfer. The addressing and encoding cycles consume the maximum available bandwidth. In extreme cases, large system transmission capacity depends on the bus's maximum effective bandwidth. However, it is not appropriate to interface the CAN network with its 8-byte payload. Data buffering requires filling enough CAN packets into system packets. The second issue to consider is that buffering enough data for a system packet of 1 Mb/s input CAN rate may incur a large delay in CAN data. In another extreme case, the transmission capacity of the system is configured to transmit very low payloads of 1 to 4 bytes. Here too high bandwidth wastes overhead cycles for addressing and encoding.
Both MOST and Flexray are targeted at important real-time applications. For example, an audio stream from a CD player on a MOST network is transmitted at a fixed rate. Audio and video require real-time transmission. The system bus must ensure that there is no significant delay in network data from, for example, a CD player. No one wants to see gaps or echoes on the audio player. The cause of the delay is that there is too much buffered data -- system buffers that are too large in data buffer size and that are not well-formed affect latency and real-time performance. Choosing the system bus speed and the size of the packet will determine the amount of buffering required for each interface in the gateway. The amount of buffering must be determined to maintain bandwidth and meet the real-time required transmission performance requirements of devices hung on the in-vehicle network.
In an ideal architecture, the embedded processor is mostly used for processing. However, processor cycles are consumed by functions such as interrupt response and data movement. In order for the processor to operate at peak efficiency, data movement operations can be performed by dedicated hardware components. A DMA controller is an embedded hardware module for transferring data between a gateway interface (such as a MOST interface) and a memory or other interface. After the processor is configured, the DMA controller transfers data in the background while the embedded processor processes the application data.
Gateway design engineers have several design options here, the most important of which is whether or not a DMA controller is required. This depends on the embedded processor architecture. For executing data transfer applications, perhaps the processor has enough idle periods. Similarly, in order to minimize the cycle required for data transfer, each cycle of the processor is calculated, taking into account the transfer capacity and the type of DMA transfer.
As you can see, the architecture of the in-vehicle gateway needs to consider several performance factors. At least the gateway needs to meet the bandwidth and latency requirements of the interface being plugged in. The solution must be user-customizable, cost-effective, and robust to maintain competitiveness.
The problem that the gateway needs to solve
Standard parts for applications (ASSP) meet these needs, but the main problem is that their functions and features are immutable. System designers who use ASSP have little chance to differentiate their products from competitors' products. Design changes can be significant if you consider adding functionality or making adjustments based on changes in the design cycle. Customized ASIC designs typically require 18-24 months and cost-effective disposables can cost millions of dollars.
On the other hand, the use of programmable devices such as gate arrays (FPGAs) in an increasingly evolving in-vehicle network has significant advantages. FPGAs enable system designers to design unique feature sets based on their application and can adapt their designs to support changing standards and feature sets. Design engineers can embed as many processors and DMA controllers as needed for the application. The system bus bandwidth and buffer size can also be adjusted to the desired value depending on the application. This customization allows design engineers to choose the ideal cost and performance point.
In addition, programmable logic solutions can be reconfigured in the field and provide users with a channel to update new applications. Programmable device-based products have a fast time to market. Some FPGA manufacturers and partner companies provide intellectual property (IP) cores for automotive applications. By modifying the RTL parameters, users can customize these IP cores for specific applications. This allows you to optimize costs based on the problem space. System designers can also use custom logic to increase the available IP cores to differentiate their products from competitors' products.
Evolving standards and data-intensive applications such as navigation and video display require more and more IP content to shorten design cycles, programmable logic device-based in-vehicle gateways and proven IP cores are cost-effective, their solutions The flexibility is very high.
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