MIPI Spy

Hardware tools for non-invasively sniffing MIPI D-Phy links.

In order to contribute useful data to the OpenHD project, I designed a simple PCB that splices two 15-pin MIPI FFCs end-to-end, to allow non-invasive, man-in-the-middle sniffing of the data. This serves several purposes:

Non-destructive and low-risk probing of the I2C bus

No more risk of shorting or ripping pads by clipping onto the FPC connector

Latency benchmarking

Sensor ICs incorporate buffering stages between pixel capture and ISP. By probing the data lanes and a strobing light source, one can measure how long the module takes to process each pixel/line/stripe/field/frame as the delay between the strobe pulse and the first transmission of "bright" bytes on a data lane. This will help determine which modules are best suited to our low-latency application.

Accurate probing of sLVDS

Due to the sensitivity of LVDS to impedence changes and phase, the length and impedence-matched routing on the MIPI Spy presents the best possible scenario for observing the signal with minimual harm to the transmission quality. Ideally, this means 0 extra retransmissions incurred due to instrumentation. Compared to scratching the coating off of an FFC and soldering on leads, this is a major step up.

Hardware

Pi version (v1.0)

• 15-FFC (1.0mm pitch) to 15-FFC (1.0mm pitch) F/F with 15-pin breakout header (2.54 mm pitch)
• Requires 15-wire MIPI camera, 2 flex cables (one top-bottom, one top-top), and a host machine with support for the camera module
• Awaiting validation samples

DJI-A version (not done)

• Hirose DF56-26P to DF56-26P with 26-pin breakout header
• Requires 2 DJI or Caddx FPV camera cables, a DJI FPV compatible camera, and a DJI or compatible air unit
• May not be possible due to unavailability of DF56-26S connectors

DJI-B version (not done)

• Hirose DF36-30P to DF36-30P with 30-pin breakout header
• Requires 2 custom DF56-to-DF36 cables, a DJI FPV compatible camera, and a DJI or compatible air unit
• Alternative to DJI-A in case of sourcing issues
• Higher cost due to custom cable requirement

HDZero Version (not done)

• Hirose DF36-20P to DF36-20P with 20-pin breakout header
• Requires 2 HDzero "Mipi" cables, an HDZero camera, and an HDZero VTX
• According to sources, this is actually a DVP link, not MIPI