From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jaya Kumar" Subject: Re: newbie: fb specs and indirect VRAM access Date: Thu, 21 Aug 2008 09:09:52 -0400 Message-ID: <45a44e480808210609h3dadb6bdo7512eb720f54f49f@mail.gmail.com> References: <47858.200.178.190.130.1219177894.squirrel@mail2.icmc.usp.br> <34825.200.178.190.130.1219322627.squirrel@mail2.icmc.usp.br> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from sc8-sf-mx2-b.sourceforge.net ([10.3.1.92] helo=mail.sourceforge.net) by sc8-sf-list1-new.sourceforge.net with esmtp (Exim 4.43) id 1KW9vG-0001O0-3W for linux-fbdev-devel@lists.sourceforge.net; Thu, 21 Aug 2008 06:09:54 -0700 Received: from nf-out-0910.google.com ([64.233.182.188]) by mail.sourceforge.net with esmtp (Exim 4.44) id 1KW9vF-0001gT-EB for linux-fbdev-devel@lists.sourceforge.net; Thu, 21 Aug 2008 06:09:53 -0700 Received: by nf-out-0910.google.com with SMTP id g16so459893nfd.2 for ; Thu, 21 Aug 2008 06:09:52 -0700 (PDT) In-Reply-To: Content-Disposition: inline List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-fbdev-devel-bounces@lists.sourceforge.net Errors-To: linux-fbdev-devel-bounces@lists.sourceforge.net To: Geert Uytterhoeven Cc: linux-fbdev-devel@lists.sourceforge.net On Thu, Aug 21, 2008 at 8:54 AM, Geert Uytterhoeven wrote: > On Thu, 21 Aug 2008, Jorge Marques Pelizzoni wrote: >> A few days ago I sent the message below asking about framebuffer device >> documentation and explaining my specific situation. Nobody aswered and I >> wonder why. If those are not questions for this list, can someone please >> redirect me to the right forum? > > I had hoped somebody else would find time to respond ;-) > >> Jorge Marques Pelizzoni escreveu: >> > I am considering implementing a frame buffer device for a mobile platform >> > (LPC2400 on uCLinux) that, as far as I can tell, seems to lack one. Well, >> > I am a newbie to all things frame buffer-related (though familiar with >> > kernel/device module implementation) and would most appreciate it if you >> > could answer the following questions: >> > >> > 1 - are there documents specifying frame buffer devices and how >> > applications are expected to handle them (in short, their API)? > > linux/Documentation/fb/framebuffer.txt > linux/include/linux/fb.h > >> > 2 - my CPU cannot address "real" VRAM directly, all control being carried >> > out by means of a parallel interface. I gathered that an fb user is >> > expected to write to (virtual) VRAM directly via a pointer provided by the >> > driver and never notifies the driver of changes. Have you seen such a >> > set-up before and do you think these requirements can be reconciled? The >> > only way round this I can currently see is making the driver periodically >> > check the virtual VRAM for changes and transmit only changed parts. All in >> > all, a costly operation, as everything must be carried out by the same >> > CPU. Could whatever is used to implement mmap be called into play (without >> > whatever is used to implement msync)? > > linux/Documentation/fb/deferred_io.txt One note about this. If you're using LPC2400, I think that's an ARM7. TDMI so no MMU which I think matches your mention of uclinux. Unfortunately, defio has a dependency on MMU. There are other possibilities to achieve the same effect but I'm not familiar with the 2400 and I'm not sure if it can do it. ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/