camera1394: Driver hangs in external trigger mode when external clock is not supplied.

[bgromov]

The problem appeared with introduction of #9.

Due to the blocking method used in Camera1394::readData() libdc1394 will not return control until the data received from camera. The problem can be fixed fairly easy since Camera1394::readData() is already called periodically by main thread.

Also, introduction of non-blocking read method will allow implementation of polled_camera interface (#13).

[bgromov]

(As requested in #14)

To reproduce the issue:

• Set external_trigger: True
• Disconnect external trigger wire from a camera

To verify the driver is not responding:

• Update any parameter of a camera, e.g. external_trigger itself:

  rosrun dynamic_reconfigure dynparam set /camera1394 "{'external_trigger': False}"
  

  (reproduced from memory)

  Above command will not return until trigger clock supplied again.

[bgromov]

@jack-oquin, are you working on this right now? If you have not started yet, I can try to fix it myself.

The only problem I see is the interface to class Trigger which is necessary to check if external trigger's power is on. At the moment Feature::trigger_ is a private member, so there is no way to obtain this information. The switch between blocking and non-blocking read methods can also be based on dynamic_reconfigure config, but it is not reliable.

[jack-oquin]

I have no time to work on it before Monday or Tuesday.

I'll go ahead and merge your current PR (#21), making it easier to handle this separately.

I can probably respond to short messages over the weekend.

[jack-oquin]

I can confirm that this problem happens with my Sony XCD-XS90CR test camera. We need a fix.

I'll experiment with the #21 pull request after I get some of the parameter setting problems sorted out.