[Elphel-support] External trigger mode is set to ask the question, a friend of China

[Andrey Filippov]

2010/5/3 tiandylzp <tiandylzp at 126.com>

> Dear Andrey
>      Recently we are testing the camera's external trigger function,but we
> do not know how to set parameters,and which parameters are set we need
> to.Please send us some external trigger mode of the document camera,we will
> very grateful！I'm not sure, do you understand my description of the contents
> of the above,because my English is not good.
>      Can not browse the Web(
> http://www.mail-archive.com/support-list@support.elphel.com/msg00005.html)
> in China,so please send some settings document.
>

>
>
>                                           Wait for your early reply!
>
>
>                                                            Best regards,
>
>
>
>                                                                   lizhipeng
>
>                                                              2010-05-04
>

HI Lizhipeng
Is it that you can not browse mail-archive.com or other sites too?
Can you access alternative page on our server:

http://support.elphel.com/pipermail/support-list_support.elphel.com/2009-October/000005.html

If not - here is the copy of that post below

Andrey

----------------------------------------------

Andreas,

Can you please send the full list of parameters in that link you've
sent? Or was it truncated by the mailing list software? - in that case
send just parameters, not in the form of URL.

So you are first trying to set camera so the sensor will run in
external trigger mode with the periodic trigger generated in the FPGA?
There is a minor bug - you can not switch trigger modes when the timer
is off (as it is initially). Even if you change it in the same command
camera will get stuck as most logic is synchronized by the sensor
frame sync pulses. So you have to make those pulses coming before you
change the modes. Here is the procedure:

So on the page (linked from http://192.168.0.9/parsedit.php)
http://192.168.0.9/parsedit.php?embed=0.1&title=External+trigger+controls&TRIG=4&TRIG_PERIOD=19200000&TRIG_DELAY&EARLY_TIMESTAMP=1&THIS_FRAME=@&TRIG_CONDITION=0&TRIG_OUT=0&SENSOR_REGS30=@

1)Uncheck 'TRIG' line and click "Apply'. That will program the timer,
but not switch to external trigger mode
2) Then - put "4" (as it was originally) or click "Restart" button.
3) click 'Apply' again - it should not freeze anymore.

The EARLY_TIMESTAMP parameter (used in external sync mode) switches
between moments when the timestamp time is acquired. In regular (free
running) mode it hap[pens at sensor frame sync (beginning of the frame
readout) - it is OK as the exposure starts during the previous frame
readout and changing exposure time does not influence the frame
period. That is not exactly the case with external trigger mode - the
start of the readout (and frame sync) will "float" with the exposure
time that starts 8 scan lines time after the external trigger. So
using timestamps of the frame sync causes the frame period (measured
at start of readout) slightly variate when exposure time is changed
(i.e. by autoexposure algorithm) and that can confuse video streamer.
When EARLY_TIMESTAMP is set, timestamps use the trigger moment instead
of the start of the readout - that results in constant frame periods.


Andrey
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