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Message-ID: <509BAFB9.6090801@antcom.de> Date: Thu, 08 Nov 2012 14:12:25 +0100 From: Roland Stigge <stigge@...com.de> To: Alban Bedel <alban.bedel@...onic-design.de> CC: Thierry Reding <thierry.reding@...onic-design.de>, LKML <linux-kernel@...r.kernel.org>, Alexandre Pereira da Silva <aletes.xgr@...il.com> Subject: Re: [PATCH] pwm: lpc32xx - Fix the PWM polarity 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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