Hi, Thanks for looking into this. On Wed, Oct 1, 2014 at 4:55 AM, Tomasz Figa <tomasz.figa@xxxxxxxxx> wrote: >> I think that comment is incorrect. If tcmp is written as -1UL then the >> LED totally turns off. And there is nothing in the Exynos4412 manual >> to suggest that -1UL should be set in the TCMP register for 100% duty. > > Looking at Figure 11-3 in 11.3.2 Basic Timer Operation chapter of Exynos > 4412 public datasheet [1] (page 659), the calculation above seems > correct. The default state of timer output is high and if TCMP is set to > a value higher than TCNT, then it will never toggle to low. > > [1] > http://www.samsung.com/global/business/semiconductor/file/product/Exynos_4_Quad_User_Manaul_Public_REV1.00-0.pdf I read that diagram a bit differently. The default state of the output is high, but that is while PWM is "inactive". It goes low at the point when the timer starts, and it also goes low when the timer later restarts every time. So once we enable PWM the output should be low. It will go high once TCMP == TCNT, but because TCMP is placed at the maximum value which is never hit, that will never happen, so the LED stays off. But I am confused on a few counts here... I may have identified above why a maximum TCMP value would not result in the output going high, but then why does the rest of the brightness scale work? If I set brightness 200 (tcmp=6470, tcnt=29999) then the LED is on dimly. If I set brightness 254 (tcmp=117, tcnt=29999) then the LED comes on much brighter. But according to my above explanation and looking at the diagram you referenced, such a decrease in the tcmp value would result in a shorter time for which the output is high, i.e. lower brightness, but actually the brightness increases. If the output is high by default, why don't I see the LED turning on in uboot before Linux has even loaded? Does the above diagram really apply to Linux? Because Linux sets the invert bit for all the channels in pwm_samsung_probe. So maybe that diagram is irrelevant until we invert the TOUT signal shown there? Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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