[Elphel-support] External triggering

[Andrey Filippov]

Ángel,

Couple more notes about external triggering.

 This is a "Electronic Rolling Shutter" sensor, so there are some natural
limitations on what you can do with external triggering. If you want just to
synchronize two cameras - it is easy, but you can not trigger the camera
that way from a flash (there are some other ways how to do that). External
trigger on the sensor level work in the following way:
1 - sensor waits for the trigger to occur, to data and sync signals are
output
2 - after the trigger sensor skips 8 scan lines (for some internal reasons)
3 - sensor _starts_ to erase scan line - one by one - the it will take about
1/15 seconds to clear the full 5 MPix frame
4 - after waiting specified exposure time from start of the erasing process
(sensor does not need to wait the full frame to be erased!) sensor starts
readout - line by line, at the same pace the erase process (initiated at
step 3).
The process of readout (and so exposure of the last line in the frame) will
ens in 8*scan_line_time + exposure time + frame_readout_time.

If you want to catch some instantaneous event (i.e. flash) you'll need to
set exposure time to > frame readout time and initiate that event after the
full frame is erased but before the first line is read out.

Second note is related to the camera driver - because of pipeline operation
(described in
http://www.linuxfordevices.com/c/a/Linux-For-Devices-Articles/Elphel-camera-under-the-hood-from-Verilog-to-PHP/)
it heavily depends on the frame sync pulses from the sensor. So if the
sensor is stopped so is the driver that among others handle all the
parameter changes. If the camera is set to external trigger mode and there
is no trigger coming - the driver will effectively get stuck.

Andrey
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://support.elphel.com/pipermail/support-list_support.elphel.com/attachments/20100202/00114cfb/attachment-0002.html>