From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brownell Subject: Re: [[RFC] 2/5] Emulates PWM hardware using a high-resolution timer and a GPIO pin Date: Tue, 17 Nov 2009 01:29:36 -0700 Message-ID: <200911170029.36669.david-b@pacbell.net> References: <1255984366-26952-1-git-send-email-bgat@billgatliff.com> <1255984366-26952-2-git-send-email-bgat@billgatliff.com> <1255984366-26952-3-git-send-email-bgat@billgatliff.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1255984366-26952-3-git-send-email-bgat@billgatliff.com> Content-Disposition: inline Sender: linux-embedded-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Bill Gatliff Cc: linux-embedded@vger.kernel.org Worth highlighting that this is necessarily a "low quality" PWM ... in the sense that it's got lots of jitter because of needing CPU intervention in IRQ context, so it's subject to delays from both IRQs being blocked and from other timer driven activities firing first. There are lots of applications where that jitter is enough to preclude using this kind of PWM. I get the feeling that some of the Linux folk seeing "this PWM thing" are not very cognizant of such issues ... they've not had to use PWM to do anything where the jitter matters. (Not that I have; but I know that such apps are a motivation for most of the PWM hardware on microcontrollers. A few PWMs plus some sensors, hall effect or QEI or whatever; then you get a motor controller.) - Dave