Camera Serial Interface

The Camera Serial Interface (CSI) is a specification of the Mobile Industry Processor Interface (MIPI) Alliance. It defines an interface between a camera and a host processor. The latest active interface specifications are CSI-2 v3.0, CSI-3 v1.1 and CCS v1.0 which were released in 2019, 2014 and 2017 respectively.[1][2][3]

Standards

CSI-1

CSI-1 was the original standard MIPI interface for cameras. It emerged as an architecture to define the interface between a camera and a host processor. Its successors were MIPI CSI-2 and MIPI CSI-3, two standards that are still evolving.

CSI-2

The MIPI CSI-2 v1.0 specification was released in 2005. It uses either D-PHY or C-PHY (Both standards are set by the MIPI Alliance) as a physical layer option. The protocol is divided into the following layers:

  1. Physical Layer (C-PHY/D-PHY)
  2. Lane Merger Layer.
  3. Low Level Protocol Layer.
  4. Pixel to Byte Conversion Layer
  5. Application Layer

In April 2017, the CSI-2 v2.0 specification was released. CSI-2 v2.0 brought support for RAW-16 and RAW-20 color depth, increase virtual channels from 4 to 32, Latency Reduction and Transport Efficiency (LRTE), Differential Pulse-Code Modulation (DPCM) compression and scrambling to reduce Power Spectral Density.[4]

In September 2019, the CSI-2 v3.0 specification was released. CSI-2 v3.0 introduced Unified Serial Link (USL), Smart Region of Interest (SROI), End-of-Transmission Short Packet (EoTp) and support for RAW-24 color depth.[5][6]

CSI-3

MIPI CSI-3 is a high-speed, bidirectional protocol primarily intended for image and video transmission between cameras and hosts within a multi-layered, peer-to-peer, UniPro-based M-PHY device network. It was originally released in 2012 and got re-released in version 1.1 in 2014.[7]

Camera Command Set (CCS)

The Camera Command Set (CCS) v1.0 specification was released on November 30, 2017. CCS defines a standard set of functionalities for controlling image sensors using CSI-2.[8][9]

Technology & Speeds

For EMI reasons the system designer can select between two different clock rates (a and b) in each of the M-PHY speed levels.[10]

M-PHY speed Clock rate Bit rate
Gear 1 G1a 1.25 Gbit/s
G1b 1.49 Gbit/s
Gear 2 G2a 2.5 Gbit/s
G2b 2.9 Gbit/s
Gear 3 G3a 5 Gbit/s
G3b 5.8 Gbit/s

References
  1. "MIPI Camera Serial Interface 2 (MIPI CSI-2)". MIPI Alliance.
  2. "MIPI Camera Serial Interface 3 (MIPI CSI-3)". MIPI Alliance.
  3. "MIPI Camera Command Set (MIPI CCS)". MIPI Alliance.
  4. "MIPI Alliance Expands Popular CSI-2 Camera Specification Beyond Mobile". MIPI Alliance. April 5, 2017.
  5. "New Version of Most Widely Used Camera and Imaging Interface—MIPI CSI-2—Designed to Build Capabilities for Greater Machine Awareness". MIPI Alliance. September 26, 2019.
  6. "VIP Central > MIPI CSI-2 v3.0 is here! – The industry's First Comprehensive Solution for 5G, Imaging, Surveillance and Automotive". blogs.synopsys.com. Retrieved 2019-09-28.
  7. MIPI Camera Serial Interface 3 (MIPI CSI-3)
  8. "MIPI Alliance Releases MIPI CCS, a New Specification that Streamlines Integration of Image Sensors in Mobile Devices". MIPI Alliance. November 30, 2017.
  9. "An Interface to Make Installing Image Sensors Easier". Electronic Design. 2017-11-30. Retrieved 2019-09-28.
  10. Understanding MIPI Alliance Interface Specifications


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