The EVDK or VIP from Lattice Semiconductor (Embedded Vision Development Kit) is a stereo camera reference design for development of machine vision or surveillance applications. It is based on a ECP5 FPGA as main processing unit and a CrossLink (LIF-MD6000) for sensor interface conversion. As an add-on, a GigE and USB vision capable output board can be purchased and is required for this demo.
The image acquisition board of the VIP is equipped with two rolling shutter sensors IMX214 from Sony. Unfortunately, their register map is not publicly available. The on board CrossLink unit translates video data coming through two MIPI interfaces into a parallel video stream which is easier to handle by the processor board. There are two different default firmware images for the CrossLink:
- Stereo mode: both sensor’s images are merged at half the x resolution (cropped)
- Mono mode: Only image data coming from Sensor CN2 is forwarded
The CrossLink bit files are available at Lattice Semi after registration [ Link ]
The MJPEG streaming bit file is available for free [ MJPEG-Streaming-Bitfile-for-VIP ].
As reference receiver for the JPEG RFC2435 stream we use the gstreamer pipeline framework. Create a script as follows:
caps="application/x-rtp, media=\(string\)video," caps="$caps clock-rate=\(int\)90000," caps="$caps encoding-name=\(string\)JPEG" gst-launch-1.0 -v udpsrc \ caps="$caps" \ port=2020 \ ! rtpjpegdepay \ ! jpegdec \ ! autovideosink
When calling this script under Linux (as well as under Windows) gstreamer runs a RTP MJPEG decoding pipeline and displays the video strom as soon as it arrives. The stream must then be configured on the VIP.
- Connect USB programmer cable to VIP processor board. Then start a terminal (like minicom) with serial parameters 115200 bps, 8N1
- Connect to /dev/ttyUSB1 (Linux) or the corresponding virtual COM port on Windows
- Load ECP5 MJPEG encoder reference design (bit file) onto the target using the Diamond Programmer
- On the console, configure address of receiver:
- Verify ARP reply:
# Got ARP reply: 44 ac de ad be ef
- Start JPEG-Video, e.g. 1920×1080 @ 12fps (slow bit rate):
If the JPEG stream stops, the reason is mostly a bottleneck in encoding. Under certain circumstances, FIFO overflows can be provoked by holding a colorful cloth in front of the camera. Also, a fully white saturation may fill up the FIFOs in this demo. The JPEG encoder is configured to allow up to five overflows before terminating the stream. For detailed error analysis, see documentation of MJPEG Encoder.
Sensor parameter configuration
The connected sensors are configured via the i2c bus:
# scan i2c-Bus (only when JPEG stream off):
# i2c register query (hexadecimal values):
# set i2c register:
i 100 1
Simplified sensor access (also, values are in hexadecimal notation):
|sh [0|1]||HDR mode|
|sr [Gain]||Gain red|
|sg [Gain]||Gain green|
|sb [Gain]||Gain blue|
These are JPEG images captured from the encoded stream without further conversion. They use the Crosslink firmware for stereo sensor configuration. Image errors can occur due to probable synchronization issues at a lower pixel clock.
- Video does not start:
- Check error messages on console. If ‘Frames received’ upon video stop (‘j’) shows 0, the sensor configuration may be incorrect or the CrossLink is not properly initialized.
- Check for Network activity (orange LED) on GigE board
- Use wireshark to monitor network activity
- Video starts, but terminates:
- Check error bits on console: [DEMUX], [FIFO], …
- Increase quantisation value (better compression):
- Check for lost packets with wireshark
- Try direct network connection between VIP and PC (no intermediate router)
- Broken images:
- Check again for error bits on console. It is also possible, that the CrossLink reference design does not properly handle the clock coming from the sensor.
The imx214 sensors are configured using the ‘default’ sequence from the reference design, but at a lower PLL frequency around 54 MHz. Both sensors are started synchronously.
Single camera configuration
This setup uses the single camera bit file provided from Helion Vision.
- Framing errors occur early in the entire video stream, then it runs stable for a very long time (recorded up to 150’000 frames)
Dual camera configuration
This setup uses the stereo camera reference design from the Lattice website (DualCSI2toRaw10_impl1.bit).
- Framing very unstable, right image shows interesting color shift
- Offset changing from frame to frame, displaying as above
The reason for the occuring DEMUX errors from the JPEG encoder is occasional invalid framing. Frames are then dropped and the image is out of sync.
- Framing from sensor is wrong (critical sensor configuration mode)
- Framing from Sensor correct, but translation hickups inside CrossLink
- Irregular timing (too short Hblank time) stressing the JPEG encoder FIFOs
(1) can not be verified without a MIPI timing debugger. (2) can not be simulated due to closed source of CrossLink Firmware.
For (3), the LINE_VALID (blue) and FRAME_VALID (yellow) signals, both routed to external debug header display as follows:
The above behaviour of two subsequent pixel lines with short blanking time occur in the current Stereo and single sensor CrossLink firmware configuration.
Sorted by ascending complexity:
- Find magic setting for more regular MIPI data transfer
- Use another sensor (parallel interface)
- Try to fix irregular timing by a ‘sanity checker’ interface with line buffer
- Revisit Crosslink firmware (consider fixes by third party)