Detecting Blank Screen

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Detecting Blank Screen

Postby timmac » Mon Apr 30, 2012 9:03 am

The current project I am working on is for a Medical application and for Hazard Analysis
there is a need to determine if the screen is blank or not.

Is this possible via Storyboard? Nothing strikes me looking through the documentation.

Thanks,

Tim
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Re: Detecting Blank Screen

Postby jason » Mon Apr 30, 2012 2:05 pm

I guess what is the case(s) you are trying to detect?

Reasons the screen would be blank that I can think of

1 - You didn't put anything on the screen

Don't do that :) But you could use the screen dump action to create a bmp of the current screen and verify that every pixel isn't black.

2 - sbengine crashed or has gone off the rails

You'd have to detect the crash and restart, but hopefully this never happens.

3 - hardware failure

Not sure what you can do here???

4 - power mode switched the lcd off

On linux this can be controlled and check by reading from a path in /sys/class/graphics/fb0
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Re: Detecting Blank Screen

Postby timmac » Tue May 01, 2012 7:52 am

Jason,

Since the device will be used in surgeries, if the LCD for any reason is not able to provide feedback
to the operator we need to disable the ability to adjust some switches that allow the user to control
various settings and go into a fail safe mode.

I think the screendump should work fine as I was considering just getting a pointer to the frame
buffer (we are running on QNX) and checking to see if each pixel is black.

Thanks,

Tim
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Re: Detecting Blank Screen

Postby brian » Tue May 01, 2012 7:10 pm

Hi,

I am not sure that the screendump functionality will give you what you need. Screendump dumps the contents of the framebuffer which may be in system memory or in graphics memory depending on the system. This may be valid data even if the lcd is not responding due to a hardware malfunction or cabling error. So the dump may work for some things but if you have a failure on the lcd the framebuffer may still show valid data.

Brian
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Re: Detecting Blank Screen

Postby timmac » Thu May 03, 2012 9:16 am

Thanks Brian - I will write a routine using the QNX framebuffer pointer.
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