What Is GMSL2?

GMSL2, the second generation of Gigabit Multimedia Serial Link, is a serialiser-deserialiser (SerDes) technology from Maxim Integrated, now part of Analog Devices. It was designed to connect cameras and displays around a car, and it has become a common way to connect several cameras to an edge AI computer on robots, vehicles and drones.

Most image sensors output MIPI CSI-2, a parallel-lane interface that only reaches a few tens of centimetres. GMSL2 puts a serialiser chip in the camera, which converts the CSI-2 stream into a single high-speed serial signal. At the computer, a deserialiser turns it back into CSI-2 for the processor. The link carries uncompressed video at up to 6 Gb/s in one direction, and a slower reverse channel, around 187.5 Mb/s, for camera control, configuration and trigger signals.

Power travels down the same coax (power over coax), so each camera needs only one cable. Because the video is uncompressed and the link adds very little delay, GMSL2 suits real-time perception, where a robot or vehicle has to react to what its cameras see within milliseconds.

GMSL2 solves the distance problem of MIPI cameras without the compression and network delay of IP cameras.

GMSL2 is one of several ways to get camera data into an edge computer. The right choice depends on cable length, latency and how many cameras you need.

Texas Instruments’ FPD-Link III is the main alternative SerDes family. It works on the same principle, but GMSL and FPD-Link chips are not compatible with each other, so the camera and the computer must use the same family.

The first generation, GMSL1, carried up to around 3 Gb/s and is still found on older cameras. GMSL2 raised the forward rate to 3 or 6 Gb/s and is the generation most edge AI cameras use today. GMSL3 doubles it again to 12 Gb/s for higher-resolution sensors. The generations are not interchangeable by default: a GMSL2 camera needs a GMSL2 deserialiser, although some deserialisers, such as the MAX96712, can also run GMSL1 cameras in a compatibility mode. Check the camera and capture card datasheets together before mixing generations.

Most GMSL2 faults come from the cable rather than the electronics. Use 50 ohm automotive coax rated for the link speed, keep bends gentle and avoid adaptors and inline joints where possible, because each one adds loss and reflections. FAKRA connectors are colour-coded and keyed by code letter, so a cable for one position cannot be plugged into the wrong socket by mistake. On vehicles and machines, clamp the cable along its route, protect it where it passes moving parts and check that the connectors are rated for the vibration and temperature of the installation. Our explainer on coaxial cable covers the construction and shielding behind these limits.

NVIDIA Jetson modules accept MIPI CSI-2 natively, so a GMSL2 deserialiser board on the carrier, or a GMSL2 capture card, connects the cameras. A quad deserialiser such as the MAX96712 takes four cameras, and boards with two of them take eight cameras on one Jetson AGX Orin. The camera driver and device tree have to match the deserialiser and sensor, which is why GMSL2 systems are normally supplied as a validated set.

Our GMSL cameras include global shutter, 4K HDR and IP67 stereo models, and our GMSL frame grabbers add GMSL2 inputs to Jetson systems. The autonomous tractor case study runs eight GMSL2 cameras on one Jetson AGX Orin computer, and our guide to GMSL technology for industrial edge AI goes into cabling and system design in more depth.

We supply GMSL2 cameras, frame grabbers and rugged Jetson computers as matched sets as standard, with the drivers and device tree installed and every camera input tested before the system ships.