start.s

arm的bootloader代码,很详细

/*
 *  armboot - Startup Code for SA1100 CPU
 *
 *  Copyright (C) 1998	Dan Malek <[e-mail]>
 *  Copyright (C) 1999	Magnus Damm <kieraypc01.p.y.kie.era.ericsson.se>
 *  Copyright (C) 2000	Wolfgang Denk <[e-mail]>
 *  Copyright (c) 2001	Alex Z黳ke <[e-mail]>
 *
 * 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"


/*
 *************************************************************************
 *
 * Jump vector table as in table 3.1 in [1]
 *
 *************************************************************************
 */


.globl _start
_start:	b       reset
	ldr	pc, _undefined_instruction
	ldr	pc, _software_interrupt
	ldr	pc, _prefetch_abort
	ldr	pc, _data_abort
	ldr	pc, _not_used
	ldr	pc, _irq
	ldr	pc, _fiq

_undefined_instruction:	.word undefined_instruction
_software_interrupt:	.word software_interrupt
_prefetch_abort:	.word prefetch_abort
_data_abort:		.word data_abort
_not_used:		.word not_used
_irq:			.word irq
_fiq:			.word fiq

	.balignl 16,0xdeadbeef


/*
 *************************************************************************
 *
 * Startup Code (reset vector)
 *
 * do important init only if we don't start from memory!
 * relocate armboot to ram
 * setup stack
 * jump to second stage
 *
 *************************************************************************
 */

/*
 * CFG_MEM_END is in the board dependent config-file (configs/config_BOARD.h)
 */
_TEXT_BASE:
	.word	TEXT_BASE

.globl _armboot_start
_armboot_start:
	.word _start

/*
 * Note: armboot_end is defined by the (board-dependent) linker script
 */
.globl _armboot_end
_armboot_end:
	.word armboot_end

/*
 * _armboot_real_end is the first usable RAM address behind armboot
 * and the various stacks
 */
.globl _armboot_real_end
_armboot_real_end:
	.word 0x0badc0de

#ifdef CONFIG_USE_IRQ
/* IRQ stack memory (calculated at run-time) */
.globl IRQ_STACK_START
IRQ_STACK_START:
	.word	0x0badc0de

/* IRQ stack memory (calculated at run-time) */
.globl FIQ_STACK_START
FIQ_STACK_START:
	.word 0x0badc0de
#endif


/*
 * the actual reset code
 */

reset:
	/*
	 * set the cpu to SVC32 mode
	 */
	mrs	r0,cpsr
	bic	r0,r0,#0x1f
	orr	r0,r0,#0x13
	msr	cpsr,r0

	/*
	 * we do sys-critical inits only at reboot,
	 * not when booting from ram!
	 */
#ifdef CONFIG_INIT_CRITICAL
	bl	cpu_init_crit
#endif

relocate:
	/*
	 * relocate armboot to RAM
	 */
	adr	r0, _start		/* r0 <- current position of code */
	ldr	r2, _armboot_start
	ldr	r3, _armboot_end
	sub	r2, r3, r2		/* r2 <- size of armboot */
	ldr	r1, _TEXT_BASE		/* r1 <- destination address */
	add	r2, r0, r2		/* r2 <- source end address */

	/*
	 * r0 = source address
	 * r1 = target address
	 * r2 = source end address
	 */
copy_loop:
	ldmia	r0!, {r3-r10}
	stmia	r1!, {r3-r10}
	cmp	r0, r2
	ble	copy_loop

	/* set up the stack */
	ldr	r0, _armboot_end
	add	r0, r0, #CONFIG_STACKSIZE
	sub	sp, r0, #12		/* leave 3 words for abort-stack */

	ldr	pc, _start_armboot

_start_armboot:	.word start_armboot


/*
 *************************************************************************
 *
 * CPU_init_critical registers
 *
 * setup important registers
 * setup memory timing
 *
 *************************************************************************
 */


/* Interupt-Controller base address */
IC_BASE:	.word	0x90050000
#define ICMR	0x04


/* Reset-Controller */
RST_BASE:		.word   0x90030000
#define RSRR	0x00
#define RCSR	0x04


/* PWR */
PWR_BASE:		.word   0x90020000
#define PSPR    0x08
#define PPCR    0x14
cpuspeed:		.word   CFG_CPUSPEED


cpu_init_crit:
	/*
	 * mask all IRQs
	 */
	ldr	r0, IC_BASE
	mov	r1, #0x00
	str	r1, [r0, #ICMR]

	/* set clock speed */
	ldr	r0, PWR_BASE
	ldr	r1, cpuspeed
	str	r1, [r0, #PPCR]

	/*
	 * before relocating, we have to setup RAM timing
	 * because memory timing is board-dependend, you will
	 * find a memsetup.S in your board directory.
	 */
	mov	ip,	lr
	bl	memsetup
	mov	lr,	ip

	/*
	 * disable MMU stuff and enable I-cache
	 */
	mrc	p15,0,r0,c1,c0
	bic	r0, r0, #0x00002000	@ clear bit 13 (X)
	bic	r0, r0, #0x0000000f	@ clear bits 3-0 (WCAM)
	orr	r0, r0, #0x00001000	@ set bit 12 (I) Icache
	orr	r0, r0, #0x00000002	@ set bit 2 (A) Align
	mcr	p15,0,r0,c1,c0

	/*
	 * flush v4 I/D caches
	 */
	mov	r0, #0
	mcr	p15, 0, r0, c7, c7, 0	// flush v3/v4 cache
	mcr	p15, 0, r0, c8, c7, 0	// flush v4 TLB

	mov	pc, lr




/*
 *************************************************************************
 *
 * Interrupt handling
 *
 *************************************************************************
 */

@
@ IRQ stack frame.
@
#define S_FRAME_SIZE	72

#define S_OLD_R0	68
#define S_PSR		64
#define S_PC		60
#define S_LR		56
#define S_SP		52

#define S_IP		48
#define S_FP		44
#define S_R10		40
#define S_R9		36
#define S_R8		32
#define S_R7		28
#define S_R6		24
#define S_R5		20
#define S_R4		16
#define S_R3		12
#define S_R2		8
#define S_R1		4
#define S_R0		0

#define MODE_SVC 0x13
#define I_BIT	 0x80

/*
 * use bad_save_user_regs for abort/prefetch/undef/swi ...
 * use irq_save_user_regs / irq_restore_user_regs for IRQ/FIQ handling
 */

	.macro	bad_save_user_regs
	sub	sp, sp, #S_FRAME_SIZE
	stmia	sp, {r0 - r12}			@ Calling r0-r12
	add     r8, sp, #S_PC

	ldr	r2, _armboot_end
	add	r2, r2, #CONFIG_STACKSIZE
	sub	r2, r2, #8
	ldmia	r2, {r2 - r4}                   @ get pc, cpsr, old_r0
	add	r0, sp, #S_FRAME_SIZE		@ restore sp_SVC

	add	r5, sp, #S_SP
	mov	r1, lr
	stmia	r5, {r0 - r4}                   @ save sp_SVC, lr_SVC, pc, cpsr, old_r
	mov	r0, sp
	.endm

	.macro	irq_save_user_regs
	sub	sp, sp, #S_FRAME_SIZE
	stmia	sp, {r0 - r12}			@ Calling r0-r12
	add     r8, sp, #S_PC
	stmdb   r8, {sp, lr}^                   @ Calling SP, LR
	str     lr, [r8, #0]                    @ Save calling PC
	mrs     r6, spsr
	str     r6, [r8, #4]                    @ Save CPSR
	str     r0, [r8, #8]                    @ Save OLD_R0
	mov	r0, sp
	.endm

	.macro	irq_restore_user_regs
	ldmia	sp, {r0 - lr}^			@ Calling r0 - lr
	mov	r0, r0
	ldr	lr, [sp, #S_PC]			@ Get PC
	add	sp, sp, #S_FRAME_SIZE
	subs	pc, lr, #4			@ return & move spsr_svc into cpsr
	.endm

	.macro get_bad_stack
	ldr	r13, _armboot_end		@ setup our mode stack
	add	r13, r13, #CONFIG_STACKSIZE	@ resides at top of normal stack
	sub	r13, r13, #8

	str	lr, [r13]			@ save caller lr / spsr
	mrs	lr, spsr
	str     lr, [r13, #4]

	mov	r13, #MODE_SVC			@ prepare SVC-Mode
	msr	spsr_c, r13
	mov	lr, pc
	movs	pc, lr
	.endm

	.macro get_irq_stack			@ setup IRQ stack
	ldr	sp, IRQ_STACK_START
	.endm

	.macro get_fiq_stack			@ setup FIQ stack
	ldr	sp, FIQ_STACK_START
	.endm

/*
 * exception handlers
 */
	.align  5
undefined_instruction:
	get_bad_stack
	bad_save_user_regs
	bl 	do_undefined_instruction

	.align	5
software_interrupt:
	get_bad_stack
	bad_save_user_regs
	bl 	do_software_interrupt

	.align	5
prefetch_abort:
	get_bad_stack
	bad_save_user_regs
	bl 	do_prefetch_abort

	.align	5
data_abort:
	get_bad_stack
	bad_save_user_regs
	bl 	do_data_abort

	.align	5
not_used:
	get_bad_stack
	bad_save_user_regs
	bl 	do_not_used

#ifdef CONFIG_USE_IRQ

	.align	5
irq:
	get_irq_stack
	irq_save_user_regs
	bl 	do_irq
	irq_restore_user_regs

	.align	5
fiq:
	get_fiq_stack
	/* someone ought to write a more effiction fiq_save_user_regs */
	irq_save_user_regs
	bl 	do_fiq
	irq_restore_user_regs

#else

	.align	5
irq:
	get_bad_stack
	bad_save_user_regs
	bl 	do_irq

	.align	5
fiq:
	get_bad_stack
	bad_save_user_regs
	bl 	do_fiq

#endif

	.align	5
.globl reset_cpu
reset_cpu:
	ldr	r0, RST_BASE
	mov	r1, #0x0			@ set bit 3-0 ...
	str	r1, [r0, #RCSR]			@ ... to clear in RCSR
	mov	r1, #0x1
	str	r1, [r0, #RSRR]			@ and perform reset
	b	reset_cpu			@ silly, but repeat endlessly