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The previous article introduced the development history, advantages and disadvantages, application fields, and development direction of MIPI interfaces in detail. Today, we will delve deeper into the content of the MIPI protocol.
The MIPI specification defines the interface into two main parts: standard data transmission and control interface. The control interface is called CCI, which is a bidirectional I2C interface; data transmission is a unidirectional differential signal, called CSI, which includes a pair of differential clocks and 1-4 pairs of differential data. The figure below is a typical MIPI application illustrating the two parts of the interface.
Overall, MIPI can be divided into three layers: application layer, protocol layer, and physical layer.
Physical Layer (PHY Layer): Specifies the transmission medium (conductors), input/output circuits, and the clock mechanism for capturing “1” and “0” from the serial bit stream. This part of the specification introduces the transmission medium, electrical parameters of signals, and the timing relationship between clock and data.The physical layer specifies the Start of Transmission (SoT) and End of Transmission (EoT) markers, as well as other “out-of-band” information that can be transmitted between the transmitting and receiving physical layers. Bit synchronization and byte synchronization are also defined in this part.
Protocol Layer: The protocol layer consists of several layers, each responsible for different functions. The CSI-2 protocol allows multiple data streams to be transmitted using a single interface. The protocol layer specifies how multiple data streams are tagged and interleaved so that each data stream can be reconstructed.
The protocol layer includes three sub-layers: Pixel/Byte Packing/Unpacking Layer, which converts the pixel stream from the application layer into a byte stream for the LLP (Low-Level Protocol Layer); LLP defines the method for establishing bit synchronization and byte synchronization for serial data between SoT and EoT, and sends the data to the next layer; Lane Management Layer, which distributes the LLP data to 1/2/3/4 lanes for transmission on the sending side, and on the receiving side, it combines the data from 1/2/3/4 lanes into a data stream that can be reconstructed.
Application Layer: This layer mainly interacts with users, providing input data streams and data format information.
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