Protocol Bridges
Here are some of the more important protocol bridge solutions for video processing.
This wiki covered 11 different protocols used in video applications. If part of the video pipeline uses one protocol, and another part uses another protocol, there are protocol bridges to convert between the two protocols. Basic bridge chips do a single function, so they are comparatively easy to use, and reasonably priced. Advanced bridge chips support multiple video pipeline functions and so are more expensive and more complex.
USB Bridges View
The first thing every engineer wants is to display the image on his desktop over USB. Then he can zoom in on it, save it, or show it to others in a Zoom meeting. Here are some ways of doing that.
EZ-USB™ FX3 ($25-40 chip, $79 board) made by the Taiwanese company Infineon provide a bridge between parallel RGB and USB-3 host computers. The RGB interface looks very easy to use and is well documented. Up to 150Mhz DDR. The FX5 also supports 1/2/4/8/16 channel LVDS at rates of up to 1.25Gbits/s per lane.
FT600Q-B, FT601Q-B, and FT602Q-B ($8.50), from a British company FTDI, connect USB-3 to single ended wires using a FIFO protocol. FT600 has a 16 bits wide data path. FT601 and FR602 are 32 bits wide. The 602 version supports UVC over USB, but only send YUV422. Different versions have 1/2/4 channels. The boards cost from $66 to $74.
FTDI FT232 family provides an interface between USB 2.0, and 1/2/4/8 bit parallel single ended wires in FIFO mode. They also support SPI, UART and I2C protocols. There are versions for 1/2/4 channels, and for power flowing to the board, or in either direction. They cost $38 to $42.
Sonic SN9C291B is a Taiwanese webcam chip. It bridges a 10 bit parallel DVP to USB 2.0 high speed and full speed. To enable useable video across USB 2.0, it supports both M-JPEG and H.264 video compression.
CH569/CH565 is a Chinese RISC-V microcontroller, but the target market is bridging. It supports USB 3 host, device and HUB, SerDes at 1.25 Gbits/s, CDC, DVP with 2 frame buffers at 8/10/12-bit data width @120Mhz, or 8/16/32 bit HSPI. $35 board. Sadly the Discord server and Open Source repositories are dead, maybe because the data sheets lack crucial details. This is a common problem with Chinese products.
OmniVision, a Chinese company produces many chips which can bridge between MIPI, DVP and USB. Two chips can also merge multiple MIPI camera inputs into a single MIPI output data stream.
TinyCLUNX SOM uses a Lattice NX-33 FPGA which includes both a MIPI and USB 3 device hard cores, so it can be used to bridge between MIPI and USB-3 while also doing custom pipeline operations.
Microcontroller Bridges View
Microcontrollers can be used as a bridge between a MIPI-CSI camera and an FPGA, or between an FPGA and a display.
Clock Domain Crossing (CDC) occurs when connecting a microcontroller to an FPGA. CDC happens when the clocks are driven by different oscillators, have different frequencies, or have different phases. CDC is a problem because digital registers have setup and hold time requirements. If data changes too close to the clock edge, these timing requirements can be violated. This can cause metastability, a state where the output is unstable and can oscillate or settle to an incorrect value. MCUs have to handle CDC correctly when receiving SPI and other protocols. There is open source Verilog for CDC using FIFO queues. The GateMate FPGA includes a hardcore asynchronous FIFO controller for CDC applications.
Other Bridge Chips View
Here are described chips for bridging video protocols.
TFP410 by Texas Instruments provides a bridge between a parallel single ended video interface and DVI/HDMI. It supports up to 24bit 1600x1200 pixels at 165Mhz. Input can be 12 bits wide DDR, or 24 bits wide SDR.
SIL164 by Lattice Semi also bridges RGB to DVI. Either TFP410 or SIL164 can be used in the 1BitSquared DVI output PMOD (€22) or the Adafruit DVI/HDI Decoder ($30).
DVI to CSI bridges are used heavily in the drone industry. Here is a list of https://openhdfpv.org/hardware/cameras/hdmi-cameras-rpi/HDMI Cameras and DVI/CSI bridge boards [7].
Camera Stacks do Bridging
Several companies sell camera stacks. They usually include a sensor board, an adaptor board and a communication board. Some contain a processor board. The communication board is always a bridge chip.
Arducam USB 2/3 Shield is the base board for the Arducam camera stack. They operate at 100 Mhz and both support two cameras. The USB 2/3 version has a maximum pixel width of 14/15 single ended wires. The USB 2 version costs $92 and includes H.262 compression.
reCamera is an open source camera stack. Their stack also includes a MCU processor board, and a nice metal case for cooling the MCU.
FramOS is a camera stack for ndustrial cameras.
Protocol bridges are a low cost, and simple solution to connecting video circuits which use different protocols. Advanced bridge chips provide additional useful functionality.
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