What provides the clock signal in CSI2 interface?

Question

What provides the clock signal for the CSI2 interface used for many cameras? Does the camera provide it or is it the processor the camera is interfacing to?

Answer 1

MIPI CSI-2 data clock comes from the camera as a separate pair (D-PHY) or encoded with the signal (C-PHY).

In D-PHY both clock edges are used to sample data from the data lanes. In C-PHY every trio change-of-state encodes a clock and a multi-bit symbol, this clock is recovered by the receiver.

Now, let’s talk about the camera timebase.

Normally, the camera reference clock, or timebase, originates from the camera itself from a local crystal oscillator. This reference isn’t output by the camera directly, but the delivered data rate and frame rate would be related to it.

The host can optionally provide a reference clock to the camera, separate from the MIPI data signals, as a timebase reference. 24MHz is common.

Another method is to provide a frame sync or trigger signal to the camera. The camera will send its frame each time it is triggered.

Either way, this host-driven reference is typically used for multi-camera setups to synchronize the frames (e.g., for stereo, multi-focal or surround cameras.)