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 v4.1 (April 2024), CSI-3 v1.1 (March 2014) and CCS v1.1.1 (April 2023).[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]

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

See also

• Display Serial Interface
• Camera Link
• USB video device class

References

1. "MIPI Camera Serial Interface 2 (MIPI CSI-2)". MIPI Alliance. 4 January 2017. Archived from the original on 28 September 2019.
2. "MIPI Camera Serial Interface 3 (MIPI CSI-3)". MIPI Alliance. 4 January 2017. Archived from the original on 28 September 2019.
3. "MIPI Camera Command Set (MIPI CCS)". MIPI Alliance. 12 November 2017. Archived from the original on 2 July 2019.
4. "MIPI Alliance Expands Popular CSI-2 Camera Specification Beyond Mobile". MIPI Alliance. April 5, 2017. Archived from the original on September 28, 2019.
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. Archived from the original on September 28, 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. Archived from the original on 2019-09-04. Retrieved 2019-09-28.
7. "MIPI Camera Serial Interface 3 (MIPI CSI-3)". Archived from the original on 2018-02-07. Retrieved 2018-02-07.
8. "MIPI Alliance Releases MIPI CCS, a New Specification that Streamlines Integration of Image Sensors in Mobile Devices". MIPI Alliance. November 30, 2017. Archived from the original on September 28, 2019.
9. "An Interface to Make Installing Image Sensors Easier". Electronic Design. 2017-11-30. Archived from the original on 2019-09-28. Retrieved 2019-09-28.
10. "Understanding MIPI Alliance Interface Specifications". Archived from the original on 2023-11-10. Retrieved 2018-02-07.

External links

• MIPI Specifications