lowlevel_init.s

UBOOT 源码

/*
 * Memory Setup stuff - taken from blob memsetup.S
 *
 * Copyright (C) 1999 2000 2001 Erik Mouw ([e-mail]) and
 *                     Jan-Derk Bakker ([e-mail])
 * 2003-2004 (c) MontaVista Software, Inc.
 *
 * See file CREDITS for list of people who contributed to this
 * project.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of
 * the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 * MA 02111-1307 USA
 */


#include "config.h"
#include "version.h"


	.globl	lowlevel_init
lowlevel_init:
	/* The ADS GC+ for Linux Boot Rom Ver. 1.73 does memory init for us.
	 * However the darn thing leaves the MMU enabled before handing control
	 * over to us. So we need to disable the MMU and we use lowlevel_init
	 * to do it.
	 */

@ The following code segment was borrowed with gratitude from:
@	linux-2.4.19-rmk7/arch/arm/boot/compressed/head-sa1100.S

	@ Data cache might be active.
	@ Be sure to flush kernel binary out of the cache,
	@ whatever state it is, before it is turned off.
	@ This is done by fetching through currently executed
	@ memory to be sure we hit the same cache.
	bic	r2, pc, #0x1f
	add	r3, r2, #0x4000		@ 16 kb is quite enough...
1:	ldr	r0, [r2], #32
	teq	r2, r3
	bne	1b
	mcr	p15, 0, r0, c7, c10, 4	@ drain WB
	mcr	p15, 0, r0, c7, c7, 0	@ flush I & D caches

	@ disabling MMU and caches
	mrc	p15, 0, r0, c1, c0, 0	@ read control reg
	bic	r0, r0, #0x0d		@ clear WB, DC, MMU
	bic	r0, r0, #0x1000		@ clear Icache
	mcr	p15, 0, r0, c1, c0, 0

	nop
	nop
	nop
	nop
	nop

	b	2f
2:
	nop
	nop
	nop
	nop
	nop


	mov	pc, lr