September 3, 2021
With the continuous improvement of camera pixels (800w, 3000w, 6000w), the frame rate should reach 30 frames/s, and the transmission speed is getting higher and higher. The mipi transmission protocol has surpassed the serial and parallel transmission methods and has become a popular new data transmission standard in the market. .
MIPI is the abbreviation of Mobile Industry Processor Interface.
There are multiple organizations under the MIPI Alliance, including the High-Speed Multipoint Link Working Group (including the high-speed connection between baseband, application processor, camera module, Bluetooth, and wifi), software working group, and display Interface working group, storage interface, and working group responsible for marketing. Among them, the Camera working group formulated the MIPI Camera Serial Interface 1.0 specification, Camera Serial Interface 2 v1.0 (CSI-2).
1,Explanation of terms
DCS (DisplayCommandSet): DCS is a standardized command set for display modules in command mode.
DSI: DisplaySerialInterface, defines a high-speed serial interface between the processor and the display module.
CSI: CameraSerialInterface, defines a high-speed serial interface between the processor and the camera module.
D-PHY: Provides the physical layer definition of DSI and CSI
CIS (cmos image sensor) only uses csi-2 (camera serial interface second generation, identification generation requirements) and D-phy (physical layer, output channel requirements) in the mipi protocol. The camera end is a transmitter, and the platform end is a receiver.
In short, the role of mipi is:
1.Parallel data conversion into serial;
2.Function multiplexing, saving transmission lines;
3.Relatively improve transmission quality and speed;
4.Increase the transmission distance;
5.Applicable to new platform requirements.
CSI-2 provides specifications for the data transmission and control of the sender and receiver, and physically includes the control part and the data transmission part. The sender acts as the slave device and the receiver acts as the master device. The protocol contains three levels: physical layer, protocol layer and application layer. Its role is:
Physical layer: defines the connection mode of the physical link.
Protocol layer: It is divided into three layers (pixel packing and unpacking format, low-level protocol, link management), mainly about the way of image data packaging, and the way of processing multi-channel image data.
Application layer: The uppermost layer of the protocol, which is related to the processing of image data encoding and decoding.
Why is mipi fast?
Parallel port needs
Vsync: frame synchronization signal
Hsync: horizontal synchronization signal
And 8 data lines, but for these 10 lines, mipi only needs 5.
Clock and data reflect the difference, that is, the low bit first comes out, so it means that the differential signal P is high and N is low, and P is low and N is high.
The CSI protocol is divided into three layers:
1. Application layer (ApplicationLayer), mainly describes the data encoding and analysis in the upper data stream. The CSI-2 specification specifies the mapping of pixel values to bytes (Mapping of pixel values to bytes).
2.Protocol layer (Protocol Layer), contains several different sub-layers, each sub-layer has its own clear responsibility. Mainly include, pixel/byte packing/unpacking layer (Pixel/Byte Packing/UnpackingLayer), Low Level Protocol Layer (LLP), channel management (LaneManagement) layer.
3.The physical layer (PHYLayer) defines the transmission medium (electrical conductors), the electrical characteristics of the input/output circuit signal (electricalparameters) and the clock mechanism (timing). That is, how to obtain the "0" and "1" signals from the serial bit stream (Bit Stream). This part of the specification records the characteristics of the transmission medium and specifies the electrical parameters based on the relationship between the clock and the data channel to signal and generate the clock.