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RE: boot requirements

To: "'David Kesselring'" <dkesselr@mmc.atmel.com>, <linux-mips@linux-mips.org>
Subject: RE: boot requirements
From: "Lyle Bainbridge" <lyle@zevion.com>
Date: Thu, 24 Jul 2003 11:32:28 -0500
Importance: Normal
In-reply-to: <Pine.GSO.4.44.0307241019450.23101-100000@ares.mmc.atmel.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
Hi,

Creating a simple boot loader:

Well firstly, you'll need to at least implement some
initialization code specific to your processor. Typically
for MIPS this would involve initializing CP0, the cache
and TLB. Then perhaps some peripheral initialization such
as clocks, static memory and SDRAM controllers.  Then the
stack pointer needs to be set to a suitable location
being carefull to word align.

Ok, well that's just the reset code for your processor.
What you need to fo for the Linux kernel depends on where it
is stored and whether it is compressed. Loading from a disk
requires a slightly less than trivial bootloader. For the
sake of discussion I'll assume the kernel is located in flash:

For compressed kernel in flash with ELF header:
  a. Uncompress the kernel to RAM.
  b. Read the ELF header to determine layout of sections
     and kernel entry point.
  c. Copy sections to memory as specified in ELF header.
  d. Jump to kernel entry point.
  e. Kernel does the rest :)

If the kernel is not compress then obviously this step can
be skipped. This is a pretty minimal boot loader and easy
to implement.

> I am trying to determine what has to be included in our boot 
> code to start linux. I didn't think I needed to port yamon. 
> What does yamon or pmon provide for starting or 
> debugging(gdb) linux? Does the processor need to be in a 
> specific state or context before jumping from the boot code 
> to the linux downloaded image? If someone can point me to a 
> simple example, I would greatly appreciate it.
> 
> David Kesselring
> Atmel MMC
> dkesselr@mmc.atmel.com
> 919-462-6587
> 


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