GMSL vs MIPI: where is GMSL preferable?


High bandwidth, longer range support, data integrity, greater performance, and camera endurance will continue to be essential requirements for embedded vision applications that span many industries, including automotive, robotics, smart cities, etc. GigE, USB 3.0,USB2.0 and MIPI CSI-2 are the camera interfaces that are most frequently utilized in these applications. They can’t, however, keep up with the rising needs of many new-age apps.

Therefore, the SerDes method is extensively utilized in cable connection applications, telecom, datacom, and the industrial sector because of its high data rates, long-distance support, and better performance. The SerDes is standing behind the advantages of GMSL interfaces.

GMSL is a high-speed serial interface that is utilized in automobile video applications, robotic equipment, agricultural vehicles, and other similar applications. GMSL is a SerDes technology for long-distance transmission. How does it compare to MIPI, one of the most used camera interfaces? Discover the truth!

The finest interface is determined by a variety of parameters, including frame rate/bandwidth needs, resolution, data transfer reliability, cable length, complexity, and, of course, overall cost. To better comprehend MIPI as well as GMSL interface, their strengths and limitations, we take a detailed look at them in this post.

What is GMSL Interface?

In several industrial and embedded imaging applications, GMSL (Gigabit Multimedia Serial Link) are the best options since they are multi-purpose, low-power interfaces for delivering high-speed, high-resolution video, power, and bidirectional control data over coaxial cable or single twisted pair for advanced driver assistance systems (ADAS). Numerous robotic and smart traffic applications also make use of it.

The GMSL interface, which has a variety of interfaces like HDMI, CSI-2, DSI, asymmetric DSI, eDP, oLDI, and single/dual/quad GMSL1/GMSL2 at the input or output, is made up of families of serializers and deserializers. GMSL employs a serializer on the broadcasting side and a deserializer on the receiver end to convert data from a parallel word to a serial stream for processing.

What is MIPI Interface?

MIPI high-speed PHY specification is preferred for data transmission in a mobile terminal. With the help of this extremely flexible specification, designers may incorporate a number of crucial high-speed applications while still complying with the restrictive low-power and EMI specifications necessary for the mobile environment.

The MIPI protocol is used to transmit video and picture data between a camera as well as the host Processor speed. They are a typical part of mobile electronics. The maximum bandwidth for one of the MIPI interface types, MIPI CSI-2, is 6 Gb/s, but the actual bandwidth is around 5 Gb/s. This facilitates high-performance applications and high-resolution photography while also assisting the sensor and embedded board in working as a camera system to take images (to manage and analyze the picture data).

Comparison between the GMSL and MIPI

The GMSL camera interface satisfies the expanding requirement for high bandwidth, quick data rates, data integrity, and improved EMI/EMC performances. The following characteristics will be used to compare and contrast the GMSL and MIPI interfaces:

Transmission Distance

The GMSL SerDes technology can be more beneficial because it allows for long-distance transmission up to a 15-meter distance. These cameras can be mounted up to 15 meters distant from the host processor and still work at full speed, supporting a high frame rate and low latency. For a conventional MIPI CSI-2 camera connection, the longest permitted cable length is 30 cm.

Automatic Repeat Request

In order to ensure dependable data transmission in GMSL, the error control, and packet recovery technique known as ARQ is used. With this technique, the transmitting side can automatically retransmit packets when the receiving side doesn’t accept the packet in order to maintain error-free communication. In GMSL2, ARQ and CRC are used in conjunction to determine whether packets have been received or not. This enables the system’s critical control operations to be highly robust.

Virtual Channel Support

In accordance with the MIPI CSI-2 and CSI-3 requirements, virtual channels are supported. A GMSL deserializer can successfully decode a maximum of 16 virtual channel IDs for dual 4-lane MIPI CSI-2. The output from this deserializer is delivered by CSI-2 using virtual channel-identified packets) after this deserializer aggregates all incoming video streams.

Video Duplication

The GMSL Splitter mode, which comprises a single serializer coupled to two deserializers, is intended for display applications. It is possible to mask the output of each video pipe to each GMSL PHY in splitter mode.

The reverse splitter mode (also known as aggregation mode) is intended for camera applications, is a single deserializer coupled to two serializers.

Backward Compatibility

The backward compatibility mode is supported by GMSL1 and GMSL2 interfaces. This GMSL1 backward compatibility mode enables the GMSL2 SerDes components to function with the GMSL1 predecessor, which is identical to GMSL2. It is possible to run the GMSL2 backward compatibility mode accordingly. However, the GMSL1 and GMSL2 modes operate differently in certain ways.

After the high-speed PLL locks and the accurate clock is identified, data transmission between the SER and DES commences.

Pricing Range

The best performance is provided by GMSL cameras with longer connections; however, these are not necessary for common or short-distance applications. A GMSL camera costs more than a MIPI or USB camera since it must operate well over longer cable runs. However, there are financial benefits to employing coax cables for SerDes links rather than STP cables.

With the addition of C-PHYSM to MIPI, the system cost has decreased. However, in exceptional cases, additional development expenses may be needed if a driver for the MIPI camera is not widely available.

Final Words

One of the most widely used camera interfaces, in addition to MIPI and GMSL, is USB. However, in most situations GMSL is more preferred interface over others for embedded vision applications like robotics, ADAS, auto farm, smart traffic systems, infotainment, and so on.

Vadzo Imaging, with its immense experience in camera design, shall be able to support you with a no-obligation consultation to help you select the right interface and right technology for your solution by understanding more on your technical as well as commercial requirements.

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