I'm using Atik Titan (color) on Raspberry Pi and observing strange behavior.
For all exposures =< 0.5s everything is just fine.
For all exposures >0.51s I get horizontal bar at the top/bottom of the image
Pictures of exposure 0.5s and 0.51s are attached to the post.

Do you recognize this type of noise/distortion? Where does it come from?

Platform: armhf / raspberry pi
OS: raspbian jessie (debian 8 )
indi server: 1.0
Atik drivers: 0.25
Other: Atik Titan connected to raspberry pi through an active (powered) usb hub, both powered from the same power outlet

The solution of the problem:
You should power up your Raspberry Pi from the same USB hub you are connecting your CCD to.

Why is it important?
Powering Raspberry Pi with its own power supply will result in your CCD and Raspberry Pi do not have common ground (GND).
This leads to non-zero voltage potential on all wires between your CCD and Raspberry Pi, including data lines.
The noise identified on the images represents the current related to this non-zero voltage potential.

If you don't mind, I'll include that tip in the INDI Pi tutorial!

Sure, feel free to do so!

That's interesting, I will try that tonight. I wonder if that's why my Titan doesn't work....

I've been testing Atik Titan on Raspberry Pi for a while and... I'm 99% sure than its stability problems are related to powering the device.
Powering Atik Titan directly from RPi USB does not work or is highly unstable. You must connect it to RPi throught active (powered) USB hub.
It does matter what power supply you are using for USB hub! Atik Titan requires a lot of current (~2A) and still you need to have some (~1A) for your RPi. Therefore you should aim at 5V 3A power supply.

And the last but not least - having in mind Atik Titan is a power eater you should use USB hub that provides a lot of power to the USB ports. In many cases USB port protection applies, which limits the current below minimim required by Atik Titan. I believe this is the root cause of majority of problems with this CCD.

Good luck and let us know of the results of your tests.

I have also found out that using poor quality USB cable might result in Atik Titan not working at all OR working highly unstable OR rendering artifacts.
Shielded usb cable works for me.