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    SubjectRe: [PATCH] pwm: lpc32xx - Fix the PWM polarity
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    On Thu, Nov 8, 2012 at 11:12 AM, Roland Stigge <stigge@antcom.de> wrote:
    > On 08/11/12 12:23, Alban Bedel wrote:
    >>>> It is intended, the formular for duty value in the register is:
    >>>>
    >>>> duty = (256 - 256*duty_ns/period_ns) % 256
    >>>
    >>> Where does this modulo defined? In the Manual, there is sth. like this
    >>> defined for RELOADV (tables 606+607), but not for DUTY.
    >>>
    >>> Maybe I missed sth. in the manual. Link or hint appreciated!
    >>
    >> The manual doesn't mention this explicitly but you can see that without
    >> the modulo when duty_ns==0 DUTY would be 256, but the register is only
    >> 8 bits wide (ie. modulo 256). I made a few test and looked at the PWM
    >> output on a scope they confirm this:
    >>
    >> DUTY HIGH LEVEL
    >> 1 99.9%
    >> 25 90.0%
    >> 128 50.0%
    >> 220 10.0%
    >> 255 0.1%
    >> 0 0.0%
    >>
    >> I'll resubmit the patch with the clamping in the correct order.
    >
    > Thanks for measuring. With this, your resubmitted patch make much more
    > sense now.
    >
    > Roland

    Alban,

    I think you should include this measurements on the source code as
    comments, for future reference.

    Thanks.


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