On 08/11/12 11:33, Alban Bedel wrote: > On Thu, 08 Nov 2012 10:51:35 +0100 > Roland Stigge <sti...@antcom.de> wrote: > >> On 07/11/12 16:25, Alban Bedel wrote: >>> Signed-off-by: Alban Bedel <alban.be...@avionic-design.de> >>> --- >>> drivers/pwm/pwm-lpc32xx.c | 6 +++++- >>> 1 files changed, 5 insertions(+), 1 deletions(-) >>> >>> diff --git a/drivers/pwm/pwm-lpc32xx.c b/drivers/pwm/pwm-lpc32xx.c >>> index adb87f0..0dc278d 100644 >>> --- a/drivers/pwm/pwm-lpc32xx.c >>> +++ b/drivers/pwm/pwm-lpc32xx.c >>> @@ -51,7 +51,11 @@ static int lpc32xx_pwm_config(struct pwm_chip *chip, >>> struct pwm_device *pwm, >>> >>> c = 256 * duty_ns; >>> do_div(c, period_ns); >>> - duty_cycles = c; >>> + if (c == 0) >>> + c = 256; >>> + if (c > 255) >>> + c = 255; >>> + duty_cycles = 256 - c; >> >> Except for the range check (for the original c > 255), this results in: >> >> duty_cycles = 256 - c >> >> except for (c == 0) where >> >> duty_cycles = 1 > > No it lead to duty_cycles = 0
Let's do it step by step with the above code: c == 0 >>> + if (c == 0) >>> + c = 256; c == 256 >>> + if (c > 255) >>> + c = 255; c == 255 >>> + duty_cycles = 256 - c; c == 1 See? > >> which actually is >> >> duty_cycles = (256 - c) - 255 >> >> (think with the original c) >> >> i.e. nearly a polarity inversion in the case of (c == 0). >> >> Why is the case (c == 0) so special here? Maybe you can document this, >> if it is really intended? > > 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! Thanks, Roland -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
