From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brownell Subject: Re: Alternative Concept Date: Tue, 20 Mar 2007 00:56:59 -0700 Message-ID: <200703200057.00110.david-b@pacbell.net> References: <200703191412.l2JECLsP021909@olwen.urbana.css.mot.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <200703191412.l2JECLsP021909@olwen.urbana.css.mot.com> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: "Scott E. Preece" Cc: linux-pm@lists.osdl.org, pavel@ucw.cz, linux@dominikbrodowski.net List-Id: linux-pm@vger.kernel.org On Monday 19 March 2007 7:12 am, Scott E. Preece wrote: > = > Could you guys present a clear definition of exactly what you mean by > "clock domain" and "power domain"? I can think of several different ways > to interpret the phrases, and I'd like to end up with the same meaning > that you are arguing from... A set of devices that use the same power supply or clock are in the same "power domain" or "clock domain" (respectively). The domains will often be hierarchical, e.g. a base clock rooting other clocks, derived from it by dividers, PLL, or clock gates. Sometimes domains overlap ... e.g. a controller that needs to use one logic level for on-chip logic and another for the external interface; or similarly, different clock rates. Simple chips may not have many domains. Nowadays I think most SOCs have at least a decent selection of clock domains, to eliminate the power drain involved in driving transistors through clock ticks. I understand it's more complicated to have multiple power domains, but the incentive to shrink the leakage current is strong. (So adding on-chip power domains involves tricks to constrain leakage, and not just an ability to operate without a given power rail.) I think that captures the basics... from a software perspective. I'm sure a hardware guy could provide a more advanced course. - Dave