Answering the Top FAQs on GMSL Technology

GMSL (Gigabit Multimedia Serial Link) is a high-speed SerDes (Serializer/Deserializer) interface technology. It simultaneously transmits multiple data streams, including power and bidirectional data, over a single coaxial cable or shielded twisted pair (STP) cable, typically up to 15 meters long with lower latency and a higher frame rate.

The picture below shows the 15-meter GMSL cable that connects the camera to the host CPU.

To discover more about the GMSL interface generations, and how they work, please visit What Is GMSL Technology And How Does It Work?

Yes, GMSL2 interfaces support the backward compatibility mode.

The backward compatibility of GMSL2 is shown below.

The maximum coaxial cable length for GMSL is 15m.

Typical connectors for GMSL include FAKRA, HSD, and other automotive-grade connectors with 50Ω impedance for coaxial interface and 100Ω impedance for TWP interface.

GMSL supports both Parallel (up to 14-bit) and MIPI inputs (up to 4 lanes) as well as MIPI output (up to 4 lanes and 2.5 Gbps per lane).

Power over Coaxial (PoC) technology simultaneously transmits power and data signals over a single coaxial cable, eliminating the need for extra wiring or power circuits for remote devices like automotive cameras.

GMSL devices employ Forward Error Correction (FEC) to identify and fix bit errors that arise during video transmission over a serial link.

FEC is required for all GMSL links with compressed video to minimize the BER so that the probability of bit errors becomes negligible.

I2C/UART are serial communication protocols supported by all GMSL devices. They facilitate bidirectional, asynchronous, and serial data transmission and can also handle synchronization management issues, providing support for streaming multiple cameras.

GMSL uses ARQ, an error control and packet recovery technique, to provide dependable data transfer. This technique enables the sending side to automatically retransmit packets when the receiving side fails to acknowledge the packet to maintain error-free transmission. To determine whether or not packets are received in GMSL2, a cyclic redundancy check (CRC) is used in conjunction with ARQ. This allows for the high robustness of critical control functions in the system.

The single serializer coupled to two deserializers is called the splitter mode. Video duplication, which is the ability to mask each video pipe's output to each GMSL PHY, is feasible in this mode. The reverse splitter mode, referred to as the aggregation mode, is intended for camera applications. It is described as having two serializers coupled to one deserializer.

• Adaptive Equalization
• Asymmetric Full-Duplex Communication
• Power-over-Coax
• Sensor Data Tunneling
• Robust Data Integrity
• Reference clock over the reverse channel
• Virtual channel support
• Video duplication
• Automatic Repeat Request (ARQ) feature
• High bandwidth Uncompressed data transmission upto15m

GMSL3 is the latest generation of high-speed SerDes technology, featuring up to 12Gbps in the forward channel and 187.5Mbps in the reverse channel that supports 4K resolution at 90 fps over cable lengths of up to 15 meters with any delay.

The GMSL3 interface is designed to support backward compatibility modes with GMSL1 and GMSL2, as shown below.

GMSL3 offers three fixed forward link rates: 3 Gbps, 6 Gbps, and 12 Gbps, and a reverse link rate at 187.5 Mbps, While GMSL2 typically supports forward link rates up to 6 Gbps and reverse link rate at 187.5 Mbps. It enhances the efficiency of applications by facilitating the integration of up to three 4K streams over a single Power-over-Coax (PoC) connection, allowing for surround-view and real-time 3D imaging. These features are highly advantageous for camera-based Traffic Monitoring System and Factory Automation.

Both 50Ω coaxial and 100Ω differential pair cables (such as STP, SPP, and STQ) that adhere to the GMSL2 channel specification are supported by GMSL2 devices.

The synchronization between multiple cameras is performed to control individual cameras and to select the number of cameras to be streamed. This process yields a properly synchronized frame by ensuring multi-image capturing, multi-video recording, and multi-network streaming at different angles.

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The multi-camera synchronization can be achieved using hardware and software trigger modes.

To learn more about configuring a hardware trigger and a software trigger mode, please visit- How to implement multi-camera synchronization in smart carts the right way - e-con Systems.

These GMSL cameras are ideal for ADAS since GMSL allow longer cable lengths and higher data rates. These capabilities facilitate video data transmission over longer distances to the host processor. This GMSL camera also includes an IP69K-rated enclosure- offering protection in rugged environments such as mobile robots and heavy-duty equipment.

To learn more about camera-enabled functions of ADAS systems, please visit- How to choose the perfect camera for ADAS (Advanced Driver Assistance System) - e-con Systems

Autonomous Agriculture : GMSL cameras provide flexible connection and IP69K-rated enclosure options for large, heavy-duty equipment when using multi-camera systems and needing to situate the camera considerably from the host processor.

Autonomous Mobile Robots (AMRs) : Autonomous Mobile Robots (AMRs) use GMSL cameras for industrial tasks like material handling, transportation, and surveillance, enabling accurate observation and complex structural requirements in applications like delivery and patrol robots.

Surround View Systems : Advanced Driver Assistance Systems (ADAS) enhance the safe and efficient movement of large vehicles with surround-view systems using synchronized multi-camera setups. GMSL cameras are ideal for these applications due to their long-distance support, allowing cameras to be placed at the edges of vehicles, and industrial-rated IP69- protection.

Warehouse Robots : Warehouse Robots benefit significantly from integrating GMSL cameras due to 360-degree awareness, which is essential for effective mapping, navigation, and obstacle avoidance in complex warehouse environments. These cameras offer reliable real-time imaging even in challenging lighting conditions, ensuring that the robots can operate accurately without interruptions.

To get expert insights on other applications of GMSL2 technology with functional safety, watch our "Exclusive Webinar in collaboration with Analog Devices: Role of GMSL2 Cameras in Autonomous Systems - How It Enables Functional Safety" on YouTube.

The GMSL camera interface meets the growing demand for a 15m cable distance, high bandwidth (up to 12Gbps), data integrity, and better EMI/EMC performances.

To know the benefits of GMSL camera interfaces and their performance, please visit GMSL Camera over MIPI Camera - e-con Systems.

The GMSL3 forward link has a fixed link rate of 3Gbps, 6Gbps, or 12Gbps. The reverse link rate is also fixed at 187.5Mbps.