From owner-freebsd-hackers Mon Dec 16 17:13:06 1996 Return-Path: Received: (from root@localhost) by freefall.freebsd.org (8.8.4/8.8.4) id RAA21757 for hackers-outgoing; Mon, 16 Dec 1996 17:13:06 -0800 (PST) Received: from genesis.atrad.adelaide.edu.au (genesis.atrad.adelaide.edu.au [129.127.96.120]) by freefall.freebsd.org (8.8.4/8.8.4) with ESMTP id RAA21752 for ; Mon, 16 Dec 1996 17:13:02 -0800 (PST) Received: (from msmith@localhost) by genesis.atrad.adelaide.edu.au (8.8.2/8.7.3) id LAA23769; Tue, 17 Dec 1996 11:41:09 +1030 (CST) From: Michael Smith Message-Id: <199612170111.LAA23769@genesis.atrad.adelaide.edu.au> Subject: Re: Boot loader hacks was: Re: MAXMEM In-Reply-To: <199612161833.QAA25314@gaia.coppe.ufrj.br> from Joao Carlos Mendes Luis at "Dec 16, 96 04:33:55 pm" To: jonny@mailhost.coppe.ufrj.br (Joao Carlos Mendes Luis) Date: Tue, 17 Dec 1996 11:41:08 +1030 (CST) Cc: tony@dell.com, terry@lambert.org, eivind@dimaga.com, hackers@FreeBSD.ORG X-Mailer: ELM [version 2.4ME+ PL28 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk Joao Carlos Mendes Luis stands accused of saying: > Just a stupid question: Why does the boot loader should know if > there's more than 64M or not on the system ? Because many of the memory-detecting interfaces require real-mode calls, and the kernel has no means of performing these. > Why couldn't it simply detect 64M at most, and let the kernel > find the rest by itself ? Anyway, is what's done with the > MAXMEM option, isn't it ? > > Moreover: Is there any STRONG reason to ask the BIOS for the > memory amount ? Couldn't it search for the memory ? You can't safely "search" for memory. Systems with parity/ECC will usually NMI you if you hit a region with no memory in it, but a number of systems will just spontaneously reboot. Others will 'mirror' memory from lower locations, requiring you to write into the memory as you perform your search. Only this can disturb memory-mapped peripherals, and so it goes on. Because the BIOS has intimate knowledge of the board and chipset, it's the only authority on the subject. > Joao Carlos Mendes Luis jonny@gta.ufrj.br -- ]] Mike Smith, Software Engineer msmith@gsoft.com.au [[ ]] Genesis Software genesis@gsoft.com.au [[ ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ ]] realtime instrument control. (ph) +61-8-8267-3493 [[ ]] Unix hardware collector. "Where are your PEZ?" The Tick [[