Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261565AbVETUBz (ORCPT ); Fri, 20 May 2005 16:01:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261566AbVETUBp (ORCPT ); Fri, 20 May 2005 16:01:45 -0400 Received: from fire.osdl.org ([65.172.181.4]:63129 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S261565AbVETUBd (ORCPT ); Fri, 20 May 2005 16:01:33 -0400 Date: Fri, 20 May 2005 13:03:36 -0700 (PDT) From: Linus Torvalds To: "Richard B. Johnson" cc: Linux kernel Subject: Re: Screen regen buffer at 0x00b8000 In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1232 Lines: 38 On Fri, 20 May 2005, Richard B. Johnson wrote: > > Why can't I consistantly write to the VGA screen regen buffer > and have it appear on the screen???? Don't do it. > It looks like access there is cached??? One needs to change > VT consoles to make it appear!! No. > The screen-regen buffer at this address is hardware, in the > chip! It should not be cached! It's not cached, and it's hardware, and you don't know your VGA well enough. 0x00b8000 may be the beginning of video memory (in certain text configurations) but it is _not_ where the screen is. That is offset by the text offset register (I forget what index that is), and what you're seeing is almost certainly due to the fact that the kernel VGA console driver scrolls by just changing that offset, instead of moving lots of slow PCI memory around. Switching consoles works for you, because it ends up resetting the offset. Anyway, you really _really_ shouldn't do anything like this in the first place. Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/