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PWM glitches on iMX6

Question asked by Alexey Firago on Jun 19, 2014
Latest reply on Jun 4, 2015 by TomE

Hello all,

 

We have a custom device based on iMX6D running Android. Device has a display with a backlight controlled by the PWM from iMX. PWM frequency is 100Hz. Everything works fine except one issue. When we decreasing brightness in Android (using the slider from UI or pwm-backlight sysfs entry) from 100% to 0% (downscale), we are observing some strange glitches - some of the low impulses (from high to low) are missing. So we have long high impulse instead of high-low-high. Duration of this long impulse is equals to the expected duration of high-low-high. When this glitch is happening brightness of the screen becomes higher (since obviously we have a longer duty cycle for some time). Attached picture shows the behavior:

TEK0000.BMP.bmp

Is this some HW misconfiguration?  Is there anything in driver/settings which can be adjusted to avoid this?

 

Thanks in advance!

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