Electronic Design

Requirements For Automotive Networking

Consumer demand for more multimedia functionality in their automobiles continues to escalate. Car owners expect to find navigation systems, multifunction displays, rear-seat entertainment systems, integrated telephony, and a way to interface their latest high-tech gadgets when they roll their new wheels out of the dealer’s lot. Car stereos have become infotainment systems consisting of separate, specialized components, challenging designers to effectively communicate information between these components.

Typical applications require transfer of several channels of audio between components. Control and status information must be conveyed between components as well. Some applications also need to move data files between components.

Audio and video channels, real-time by nature, are often referred to as stream data. Stream data must be handled differently than a data file. Data files aren’t time-critical and can be broken apart, moved in pieces, and reassembled. Stream data is best transferred one sample at a time from source to sink. Storing multiple samples for bulk transfer adds the expense of data buffers at source and sink and causes system delay—both are undesirable qualities. Thus, there’s great potential for a digital communication method that supports multiple channels of digital audio and packet data over a low-cost physical layer that meets automotive quality and emissions standards.

SMSC’s new generation of networking chips, called intelligent network interface controllers (INICs), integrate network management. Therefore, the links between connected components are established and managed without external processor intervention. Since the INIC manages the network, the processor is free to manage the application. The remaining task is to establish the required data pathways through the INICs, and through the network link between components.

An application may require that four channels of 16-bit digital audio be transferred from a head unit to an amplifier. Four INIC configuration tasks are required: set up the I/O ports for the audio source/sink; create socket(s) that correspond to I/O port data; create network sockets that correspond to the required network bandwidth; and establish the connections between the I/O sockets and the network sockets (Fig. 1). Small, powerful commands from the host controller, known as Port Messages, configure the INIC.

The INIC’s audio I/O ports are flexible and support either dual I2S links, or multiplexed channels on one pin. For this example, the network bandwidth can be allocated in various ways including: one 8-byte channel that carries all four audio channels, two four-byte channels carrying stereo pairs, or four two-byte channels. The final configuration step establishes the on-chip connection between the input (or output) port and the network channel(s).

When an INIC establishes a network channel for an audio source, that channel is assigned a unique Connection Label. A node needing to extract that channel from the network must know the Connection Label and number of bytes used. With the control channel, the source node can communicate this information to the sink node. Messages transferred between nodes are interfaced to the INIC using the same Port Message protocol. A byte in the message header distinguishes INIC configuration commands from messages to other nodes. Once the desired streaming data bandwidth is assigned, the remainder of the network payload is available for packet data transfer.

In combination with SMSC’s ePHY technology, INICs can support a network bandwidth of nearly 50 Mbits/s over low-cost unshielded twisted-pair (UTP) cable. INIC’s ePHY technology achieves this high data bandwidth over UTP wire while meeting stringent automotive EMC requirements. Thus, INICs support multiple channels of digital media over a low-cost physical layer that meets automotive quality and emissions.

INIC technology can be used for either Media Oriented Systems Transport (MOST) or INIC eLITE implementations. MOST is excellent for linking several diverse components together to operate as a highly integrated system. System management is accomplished by NetServices software running on each node’s host processor. INIC eLITE is intended for simple applications that don’t need dynamic management of network resources (Fig. 2). INIC eLITE takes advantage of the integrated network management to support cost-effective and simple networks, including point-to-point links, with minimal software overhead (no NetServices).

The demand for more functionality in the car will increase as consumers become accustomed to having convenience at arms length. As designers strive to accommodate this demand, they will need versatile and easily integrated networking options. INIC eLITE and MOST technologies allow designers to integrate entry level to advanced multimedia functionality in vehicles. These options reduce the complexity and cost while allowing expandability for future functions.


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