In this section, We propose the main features of SoC buses provided in the industry. Given that the number of electronic components is increasing exponentially, point-to-point communication is not possible. The main reasons is the large number of wires needed to connect all the components, non-availability of space and in case of a failure the fault detection will be extremely difficult.
As a result, serial buses as LIN, CAN , FLEXRAY for controClling and MOST for infotainment are discussed below.
1. Controller Area Network (CAN) : CAN bus was originally proposed by Robert Bosch in the late 1980s. CAN is a multi-master bus with an open, linear structure with one logic bus line and equal nodes. Instead of point to point wiring, one serial bus is used to connect all the control systems as Safety systems like air bags and Anti-lock braking systems. For that purpose, It originally supports medium speed data rates up to 125 kbps and high speed data rates up to 1Mbps. A main feature to mention is that CAN communicates asynchronously with an event driven protocol interface along with error handling using CRC where all frame types (data, remote, error and overload frame) are transmitted in broadcast. The CAN protocol handles bus accesses according to the concept called “Carrier Sense Multiple Access with Arbitration on Message Priority”. Any node has the right to request transmission rights at any time. The necessary bus arbitration method to avoid transmission conflicts is the same: Frame with the highest assigned identifier get buss access without delay.
2. Local Interconnect Network (LIN): LIN is an asynchronous serial broadcast bus where all messages are initiated by the one single master with at most one slave replying to a given message identifier.
LIN is a low speed, single wire communication bus with data rates up to 20 Kbps which is suitable for modules where response time is not a critical issue as mirror controls and window controls.
The LIN bus is a polled bus with a single master device and one or more slave devices. The master device contains both a master task and a slave task. Each slave device contains only a slave task. Communication over the LIN bus is controlled entirely by the master task in the master device. The basic unit of transfer on the LIN bus is the frame, which is divided into a header and a response. The header is always transmitted by the master node and consists of three distinct fields: the break, synchronization (sync), and identifier (ID). The response, which is transmitted by a slave task and can reside in either the master node or a slave node, consists of a data payload and a checksum.
3. FlexRay : FlexRay networking standard for motor vehicles serves as the next step beyond CAN and LIN, enabling the reliable management of many more safety and comfort features. FlexRay suits X-by-Wire applications (i.e. Brake by Wire).
With a maximum data rate of 10 Mbps available on two channels, giving a gross data rate of up to 20Mbit/sec, FlexRay potentially offers 20 times higher net bandwidth than CAN when used in the same application.
Moreover, FlexRay allows both synchronous (real-time) using a static segment and asynchronous data transfer using a dynamic segments to meet the demand for various systems in vehicles.
FlexRay uses two methods for granting bus access to nodes TDMA (Time Division Multiple Access) and FTDMA (Flexible Time Division Multiple access).
The TDMA method uses time slots. Each FlexRay node has one or more slots assigned in which it is granted access to the bus .The communication schedule is repeated periodically by all nodes.
The FTDMA is almost the same but with flexible smaller time slots (Minislots).
Each slot of a static or dynamic segment contains a FlexRay Frame. The frame is divided into three segments: Header, Payload, and Trailer.