From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew_Klosterman@3com.com To: linuxppc-dev@lists.linuxppc.org Message-ID: <882567C2.008325F6.00@hqoutbound.ops.3com.com> Date: Tue, 3 Aug 1999 16:52:47 -0700 Subject: PPC kernel bootstrapping and relocation Mime-Version: 1.0 Content-type: text/plain; charset=us-ascii Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: I have inherited a board (developed in-house) and been tasked with porting Linux to it. I have started from the 2.2.10 kernel and have been able to get the boot process working up to the branch to identify_machine in /arch/ppc/kernel/head.S. Coming to this point, I still have some nagging questions that I hope someone with more experience porting operating systems (Linux) to PPC hardware can help me with. 1. What is the rationale behind the address at which the kernel should be compiled? There is the KERNELLOAD value defined in /arch/ppc/Makefile that is set to 0xc000_0000 as well as a value in /include/asm-ppc/page.h that defines PAGE_OFFSET and KERNELBASE to 0xc000_0000. KERNELLOAD is used as the text linkage address for the kernel, but the kernel gets relocated during the boot process. 2. Is the kernel supposed to run at 0 or at 0xc000_0000? Sure it gets compiled for 0xc000_0000, but then it gets copied down to zero by relocate_kernel in /arch/ppc/kernel/head.S. 3. Do the BATs do the necessary translation of addresses while the kernel is starting/running (wherever it end up executing at)? I haven't quite sorted out the way that memory ends up for the running kernel because I haven't yet managed to get the kernel running yet. :) 4. Ultimately, what is the view of memory that the BATs set up for the kernel? (This leads in to point #5.) 5. How can I exclude the kernel from using certain memory regions? I have some special memory areas to worry about that other hardware on this board needs. Therefore, I need to be able to exclude some memory ranges from use by the kernel. Any hints? 6. What sort of environment is the kernel expecting to be starting from? What are the default settings for the memory architecture (BATs) that is expected? I still have to deal with the peculiarities of this particular board, but I can have my own boot code set things up to a more standard configuration before passing jumping to the kernel start. Thanks for whatever aid you can contribute to yet another Linux port! --Andy Klosterman [[ This message was sent via the linuxppc-dev mailing list. Replies are ]] [[ not forced back to the list, so be sure to Cc linuxppc-dev if your ]] [[ reply is of general interest. Please check http://lists.linuxppc.org/ ]] [[ and http://www.linuxppc.org/ for useful information before posting. ]]