Embedded system developers are using the mobile processor's innovation, widely accepted MIPI standard interface, as well as a new generation of low-cost image sensors and displays to build high performance low-cost products, but still need to solve many challenges.
As performance rapid improvement, how to predict the type and quantity required for the required interface? How to use these processors to have the value of the traditional display and / or the image sensor for the value of the traditional display and / or image sensor while using these processors? How to quickly, low-cost bridges different interface types, ensure that the design is successful?
This article will introduce the impact and design issues related to the migration to new interfaces and bridge new and old devices, and introduce some feasible solutions and application methods.
Bridge new video interface
People's demand for innovative low-cost video bridge solutions is increasing. For example, constructing monitoring systems, drones or DSLR camera designers want to use the latest innovation of the on-hot mobile application processor (AP). To this end, they usually have to convert signals from the proprietary traditional image sensor interface to the mobile MIPI CSI-2 image sensor interface employed on most APs.
If the designer builds the next generation of virtual reality (VR) headphones, you need to convert a video from a single MIPI DSI interface and split it to the two MIPI DSI display. This not only improves system performance, but also the product immersion effect is stronger (Figure 1). If the AP only provides a single DSI interface or one of the available interfaces already specifically used for other features, how to support these emerging applications?
Similarly, developers of human-machine interface (HMI) solutions or intelligent displays may also wish to retain the value of huge investment in industrial grade displays. But do this, they have to receive the CSI-2 interface on the mobile AP from the OpenLDI / LVDS or dedicated interface bridge.
Sometimes, you may need to put multiple video streams to a larger frame output, creating a deep perception or enhance the reality system. At this time, a bridging solution located between the camera sensor and the image processor can be captured in time to capture multiple CSI-2 outputs in time and achieve the minimum delay. This requires universal pin control. Multiple synthetic video streams also need to share the same clock, and in some cases, a separate power-up program may be required. To implement each function, you need to be easily customized I / O.
The application of MIPI mobile processors even has deepened to traditional industrial applications, such as automotive manufacturing. With the growing number of automotive electronic equipment and the number of cameras, the advanced auxiliary driving system (ADAS) and information entertainment sonards require more video bridge.
The camera was originally developed to help the driver observed when reversing, and now the manufacturer uses the camera to provide a full range of perspectives of the vehicle. For example, some car manufacturers are replacing the rear mirror with the camera, thereby reducing air resistance and improving fuel efficiency. The video bridge solution constructed by the designer enables the manufacturer to summarize the data of multiple image sensors and transmit it through a single CSI-2 interface to the AP.
Universal switch
In order to solve the demand for the basic bridge solution, the designer generally uses universal switches. The HD3SS 3212 of Texas Instruments is a typical example of a universal 2-channel multiplexer / demultiplexer passive switch for transmitting signals between two positions on the board (Fig. 2). The device is compatible with MIPI DSI / CSI, FPDLINKII, LVDS, and PCIe Gen IIII standards support up to 10 Gbps data rates.
Designers can use the device to any interface applications that require 0 to 2 V common mode voltage range and 1800 mVPP differential amplitude. Adaptive tracking ensures that the channel remains unchanged throughout the common mode voltage range.
The HD3SS3212 comes with a variety of tools and support software, including evaluation modules and evaluation boards for USB Type-C minidock boards, and reference design with video and charging support.
Programmable solution
Another way to solve this problem is to use semi-custom or custom video bridge solutions. However, these solutions are usually focused on applicable ranges relatively narrow applications, with longer development cycles and higher non-regular engineering (NRE) costs, ASIC is a typical.
In order to make up the gap between universal and custom video bridge, video bridges require combination of design flexibility and short FPGA development cycles, as well as functionality of specific application standard products (ASSPs). For these features, we may wish to learn about the Lattice Semiconductor Crosslink LIF-MD6000 Master Link Evaluation Board and its programmable ASSP (PASSP) (Figure 3). CrossLinkIF-MD6000 is provided with the evaluation board that acts as idle IP in the Diamond Design Software of Lattice. Each PASSP surrounds two MIPI D-PHY hard blocks by moving the FPGA structure. Each MIPI D-PHY block has up to four data channels and a clock for support for transmission and reception (TX, and RX). D-PHY transmits up to 4K ultra high definition resolution, with a rate of 12 Gb / s. Two groups of programmable I / O support a variety of interfaces and protocols, including Mipi D-PHY, MIPI CSI-2, and MIPI DSI, and CMOS, RGB, MIPI DPI, MIPI DBI, SUBLVDS, SLVS, LVDS, and OpenLDI.
Adjacent FPGA structure includes 5, 936 LUT, 180 KB block RAM, and 47 KB of distributed RAM. The LUT is distributed along the dedicated register in the programmable functional unit (PFU), used as the basic component of logic, algorithography, RAM, and ROM functions. Programmable routing network connects to the PFU block.
The SYSMEM embedded block RAM (EBR) of the programmable I / O group, embedded I2C and embedded MIPI D-PHY are spread between PFU columns. The PFU block can be configured with the Diamond design software of Lattice and wiring each design.
The configuration and setting procedures have a variety of support tools and software for selection. In addition to bridge devices, the LIF-MD6000 Master Link Evaluation Board also adds the Mini USB B type connector to the FTDI. Use SPI to add FTDI to the CrossLink circuit, add FTDI to X03LF devices using JTAG and GPIO resources. At the same time, you can also browse multiple demonstrations, optional TX / RX link board information and other documentation. The kit also includes two interface boards, LIFMD-IOL-EVN SMA IO connecting interface boards and a branching IO link board. In addition, the LIF-MD6000 Raspberry PI development board includes a reference design and CrossLink soft IP to connect two Raspberry PI image sensors to a Raspberry PI processor board.
To simplify and accelerate development, Lattice Semiconductor provides a pre-design soft IP module for four common video bridge solutions. The first solution showing how to bridge multiple CSI-2 image sensors to a single CSI-2 output (Figure 4). This solution applies applications include an AP in the design that does not provide a sufficient interface that supports the number of image sensors, or a process delay between the image sensor and the imaging data.
The second solution focuses on 1: 2 and 1: 1 DSI display interface bridge. This IP objective is beyond the display capabilities for rising bandwidth requirements, while the processor continues to provide a high-performance interface function. By replacing the old displays to a new display, you can reserve huge AP input while upgrading. This bridge can also extend the output of a single source to two DSI displays instead of one.
The third example solution provides a critical IP of CMOS to MIPI D-PHY interface when using LIF-MD6000 devices. Although Mipi D-PHY is initially developed to address interconnects in smartphones and displays, many processors and displays are now still using RGB, CMOS or MIPI D-PHY interfaces. Between the processor with the RGB interface and a display with the MIPI DSI interface, or between the camera with the MOS interface and a processor with the CSI-2 interface, the solution can act as a bridge.
The fourth camera interface bridge solves the problem of mismatch between the AP and the early image sensor. Although many APs now use MIPI CSI-2 interfaces, some high-resolution image sensors use dedicated sub-LVDS output formats. This bridge solves the incompatibility between the two interface types. The bridge can also be used in LVDS, CSI-2, HISPI, and other formats of mutual conversion.
Summarize
As designers have more and more components developed for mobile handheld equipment for more applications, they often encounter the device in the system that cannot be directly connected. Sometimes the interface type or quantity on the AP does not match the image sensor or display of the system.
For some basic multiplexer / demultiplexer applications, ready-made standard analog switches may meet demand. However, as designers do some more complex bridge tasks, such as converting uncontrocious interfaces, combining multiple video streams, or splitting video streams to multiple interfaces, FPGA-based programmable bridge solutions have a number of advantages.
First, these solutions allow you to use the existing input of the old device, even if you use the image sensor and the MIPI interface of the MIPI interface, it still applies. Second, through the bridging between multiple devices of different interfaces, these bridge solutions allow you to select more components. In the end, you can achieve greater design flexibility.
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