Please give me a tip...
I faced the pwm problem for i915 as well - intel HD Graphics/Bay Trail/ Sandy Bridge... Currently I have 60Hz by default but EDID outputs I need 77.000MHz... It causes eyes strain in 20-30 minutes... I found this link https://wiki.archlinux.org/index.php/ba … 15_only.29 to solve the issue; So I installed the intel-gpu-tools but every time I input
- intel_reg_read 0x61254
or
- intel_reg_read 0xC8254
... it returns 0x0 only So I am a bit confused how do I know what address I should enter in my case and how to know the address? Please guide me
p.s kernel 3.16.5
]]>...when I have my screen brightness on the maximum ... and then bump up the PWM frequency the screen brightness immediately increases.
I don't see any changes on my hardware.
Does this mean that the maximum brightness at the previous PWM frequency was still pulsing?
Use pencil test, Luke!
]]>Also I'm puzzled by something: when I have my screen brightness on the maximum (via the hotkeys, I'm not sure what mechanism is used under the hood) and then bump up the PWM frequency the screen brightness immediately increases. Does this mean that the maximum brightness at the previous PWM frequency was still pulsing?
]]>It still seems more likely to me that you're seeing a beat frequency caused by some other signal.
Photo resistor does not shows any other frequency except 200 and some noise
I'm not sure what on that page suggests to you
I'm not sure what you have read the page. Not going to quote it here.
]]>On a screen with a 200 Hz refresh rate, powered by a battery and removed from any AC power source?
Yes, both
Interesting. It still seems more likely to me that you're seeing a beat frequency caused by some other signal. There are plenty of possible candidates.
http://www.100fps.com/how_many_frames_c … ns_see.htm
Nice site about video deinterlace.
I'm not sure what on that page suggests to you that the eye can detect flicker of a static image at rates greater than 60 Hz... but this is beginning to go way OT.
]]>On a screen with a 200 Hz refresh rate, powered by a battery and removed from any AC power source?
Yes, both
Care to elaborate?
Not really http://www.100fps.com/how_many_frames_c … ns_see.htm
Nice site about video deinterlace.
(It also happens to be right around the most hazardous frequency to be shocked at.)
Heh :E
]]>I can see 200 Hz on solid 60% gray and x2go client login screen (purple fill on right). I can even see it on default ubuntu background image if I try hard.
On a screen with a 200 Hz refresh rate, powered by a battery and removed from any AC power source?
Trent wrote:The threshold at which the human eye can observe flicker is around 60 Hz
Very common misunderstanding
Care to elaborate? I'm always willing to correct my misunderstandings...
Nope, it is all because of electricity frequency and bad filters.
That's what I meant by "coincidence". 60 Hz was a more or less arbitrary choice for AC power distribution back before TV was a thing. It just happens to approximately coincide with the flicker fusion threshold. (It also happens to be right around the most hazardous frequency to be shocked at.)
Edited for accuracy and source
]]>but I couldn't expect 200 Hz flicker to be so noticeable and hard on my eyes.
I can see 200 Hz on solid 60% gray and x2go client login screen (gray fill on right). I can even see it on default ubuntu background image if I try hard.
It might be some interference with 60 Hz refresh or something else, so it's not actually 200, like Trent said. Anyway, altering pwm freq fixed it for me.
Your flicker may be from lcd inversion (infamous Vcom voltage). Check on this page (info and inversion tests) http://www.techmind.org/lcd/
And, do you still see flicker on 700 Hz?
The threshold at which the human eye can observe flicker is around 60 Hz
Very common misunderstanding
same rate as NTSC TV (more by coincidence than by design, IIRC).
Nope, it is all because of electricity frequency and bad filters.
]]>It could also be that because the PWM frequency (200 Hz) is a whole number multiple of the AC power frequency, you're seeing a 50Hz flicker exaggerated by the fact that every "trough" in the 50Hz signal coincides exactly with another "trough" in the 200 Hz signal. You could test that theory, since you have a laptop, by disconnecting it from mains power and taking it somewhere the 50Hz signal couldn't reach you.
You could also try setting the frequency lower than 200 but not at a multiple of 50, say 188 Hz or something like that, and see if you continue to see flicker. No guarantees.
]]>This means, that 0x03000300 corresponds to 1.2 kHz. Doesn't feel safe! Lowered the value to 0x05000500 (approx. 700 Hz).
The only thing I still can't believe is that default value 1228 corresponds to 200 Hz. I understand that LEDs don't have any afterglow (comparing to CRT monitors and incandescence lamps), but I couldn't expect 200 Hz flicker to be so noticeable and hard on my eyes.
]]>Looks like it is
PWM = base clock in register 0xc6204 / 128 / 31:16 bits value in register 0xc8254.
For example, your PWM will be = 125 MHz / 128 / 0x1228 = 125000000 / 128 / 4632 = 210,829555268
...and value, you should write to 0xc8254, is = base clock / 128 / desired PWM
And don't forget about 0:15 bits in 0xc8254. Looks like it's not used on my machine, but I think it's safe to just write the same value here too, because it is said in pdf
This value overrides the CPU control of PWM duty cycle when the PWM PCH Override Enable bit is
set. This field determines the number of time base events for the active portion of the PWM backlight
control. This should never be larger than the frequency field.
So, if you get 0x1228, just write 0x12281228 to the register.
And thanks for base freq register hint.
]]>Beat is a phenomenon in which, if there are two signals that have different frequencies, say 50Hz, and 52.5Hz; the signals will mix such that an observer will perceive (see) a signal that is the sum of the two frequencies (102.5 Hz), and another that is the difference of the two frequencies (2.5Hz). The 102.5Hz will not be noticed by the human eye. The 2.5Hz will be seen as the brightness 'pulsing' every third of a second or so. What I meant by the question was, the science does not matter as long as what you see makes you happy.
In English, there is a great cliché: "Beauty is in the eye of the beholder"
]]>This value represents the period of the
PWM stream in PCH display raw clocks multiplied by 128.
In the end, I guess it is up to the observer flicker, or beat?
I'm sorry, I didn't get your last question (my English isn't good enough).
]]>But... You stated 125MHz as a reference clock, but the numerator = reg_c6204 * 128 * 1e6. Is there a disconnect between the 125 and the 128 ??
Also, I am sure your power line frequency is 50Hz. A 52Hz PWM may well beat with 50Hz flicker in your lighting to create a 2.5Hz beat frequency.
Re-running the numbers using 125 instead of 128 comes up with 51.3 Hz. That would create a more palatable 1.3Hz beat. You might play with the numbers to try to hit 50Hz exactly. On the other hand, I grew up in the world of NTSC TV rather than PAL. Our frame rate is 60Hz rather then PAL's 50Hz. Whenever I visited a country that used PAL, I was startled at how the 50Hz frame rates had noticeable flicker.
In the end, I guess it is up to the observer flicker, or beat?
Great job, by the way... This thread is probably very useful to many members.