基于友善之臂ARM-tiny4412--uboot源代码分析

/*
 * armboot - Startup Code for OMAP3530/ARM Cortex CPU-core
 *
 * Copyright (c) 2004	Texas Instruments <r-woodruff2@ti.com>
 *
 * Copyright (c) 2001	Marius Gr?ger <mag@sysgo.de>
 * Copyright (c) 2002	Alex Züpke <azu@sysgo.de>
 * Copyright (c) 2002	Gary Jennejohn <garyj@denx.de>
 * Copyright (c) 2003	Richard Woodruff <r-woodruff2@ti.com>
 * Copyright (c) 2003	Kshitij <kshitij@ti.com>
 * Copyright (c) 2006-2008 Syed Mohammed Khasim <x0khasim@ti.com>
 *
 * 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 <asm-offsets.h>
#include <config.h>
#include <version.h>

#if defined(CONFIG_S5PC110) && defined(CONFIG_EVT1) && !defined(CONFIG_FUSED)   @阶段启动相关设置
	.word 0x2000
	.word 0x0
	.word 0x0
	.word 0x0
#endif

.globl _start
_start: b	reset        @复位入口，此时使用b指令作为相对调整，不依赖执行地址

	@下面为进入异常处理函数
	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   @定义异常处理函数
_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
_pad:			.word 0x12345678 /* now 16*4=64 */  @此处保证16个字节进行对齐
.global _end_vect
_end_vect:

	.balignl 16,0xdeadbeef   @相同是保证16个字节进行对齐
/*************************************************************************
 *
 * Startup Code (reset vector)   启动代码。复位向量，此处只进行还重要的初始化操作，转移代码还有建立堆栈
 *
 * do important init only if we don't start from memory!
 * setup Memory and board specific bits prior to relocation.
 * relocate armboot to ram
 * setup stack
 *
 *************************************************************************/

.globl _TEXT_BASE
_TEXT_BASE:
	.word	CONFIG_SYS_TEXT_BASE   @此处为根文件夹下Makefile传进来的參数，详细为0xc3e00000

/*
 * These are defined in the board-specific linker script.
 */
.globl _bss_start_ofs
_bss_start_ofs:
	.word __bss_start - _start     //__bss_start在链接脚本文件里bss段開始，_end在bss段结尾,用于清除bss段。这两个值要链接时才确定

.globl _bss_end_ofs
_bss_end_ofs:
	.word _end - _start

#ifdef CONFIG_USE_IRQ
/* IRQ stack memory (calculated at run-time) */   中断栈内存
.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

/* IRQ stack memory (calculated at run-time) + 8 bytes */
.globl IRQ_STACK_START_IN
IRQ_STACK_START_IN:
	.word	0x0badc0de

/*
 * the actual reset code  复位相关的代码
 */

reset:
	/*
	 * set the cpu to SVC32 mode  设置CPU进入SVC模式
	 */
	mrs	r0, cpsr       清CPSR的第I位
	bic	r0, r0, #0x1f
	orr	r0, r0, #0xd3
	msr	cpsr,r0

#if (CONFIG_OMAP34XX)
	/* Copy vectors to mask ROM indirect addr */
	/ *拷贝载体掩模ROM间接地址*/
	adr	r0, _start		@ r0 <- current position of code
	add	r0, r0, #4		@ skip reset vector
	mov	r2, #64			@ r2 <- size to copy   r2寄存器进行拷贝
	add	r2, r0, r2		@ r2 <- source end address
	mov	r1, #SRAM_OFFSET0	@ build vect addr
	mov	r3, #SRAM_OFFSET1
	add	r1, r1, r3
	mov	r3, #SRAM_OFFSET2
	add	r1, r1, r3
next:
	ldmia	r0!, {r3 - r10}		@ copy from source address [r0]
	stmia	r1!, {r3 - r10}		@ copy to   target address [r1]
	cmp	r0, r2			@ until source end address [r2]
	bne	next			@ loop until equal */
#if !defined(CONFIG_SYS_NAND_BOOT) && !defined(CONFIG_SYS_ONENAND_BOOT)
	/* No need to copy/exec the clock code - DPLL adjust already done
	 * in NAND/oneNAND Boot.
	 */
	 @这里不须要复制/执行时钟代码数字锁相环调整已经完毕在NAND / OneNAND启动。
	bl	cpy_clk_code		@ put dpll adjust code behind vectors
#endif /* NAND Boot */
#endif
	/* the mask ROM code should have PLL and others stable */
	/ *屏蔽代码应该有锁相环和其它稳定* /
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
	bl	cpu_init_crit
#endif

/* Set stackpointer in internal RAM to call board_init_f */
call_board_init_f:
	ldr	sp, =(CONFIG_SYS_INIT_SP_ADDR)
	bic	sp, sp, #7 /* 8-byte alignment for ABI compliance */
	ldr	r0,=0x00000000
	bl	board_init_f

/*------------------------------------------------------------------------------*/

/*
 * void relocate_code (addr_sp, gd, addr_moni)
 *
 * This "function" does not return, instead it continues in RAM
 * after relocating the monitor code.
 *
 */
	.globl	relocate_code
relocate_code:
	mov	r4, r0	/* save addr_sp */
	mov	r5, r1	/* save addr of gd */
	mov	r6, r2	/* save addr of destination */

	/* Set up the stack						    */
stack_setup:
	mov	sp, r4

	adr	r0, _start
#if defined(CONFIG_S5PC110) && defined(CONFIG_EVT1) && !defined(CONFIG_FUSED)
	sub	r0, r0, #16
#endif
#ifndef CONFIG_PRELOADER
	cmp	r0, r6
	beq	clear_bss		/* skip relocation */
#endif
	mov	r1, r6			/* r1 <- scratch for copy_loop */
	ldr	r2, _TEXT_BASE
	ldr	r3, _bss_start_ofs
	add	r2, r0, r3		/* r2 <- source end address	    */

copy_loop:
	ldmia	r0!, {r9-r10}		/* copy from source address [r0]    */
	stmia	r1!, {r9-r10}		/* copy to   target address [r1]    */
	cmp	r0, r2			/* until source end address [r2]    */
	blo	copy_loop

#ifndef CONFIG_PRELOADER
	/*
	 * fix .rel.dyn relocations
	 */
	ldr	r0, _TEXT_BASE		/* r0 <- Text base */
	sub	r9, r6, r0		/* r9 <- relocation offset */
	ldr	r10, _dynsym_start_ofs	/* r10 <- sym table ofs */
	add	r10, r10, r0		/* r10 <- sym table in FLASH */
	ldr	r2, _rel_dyn_start_ofs	/* r2 <- rel dyn start ofs */
	add	r2, r2, r0		/* r2 <- rel dyn start in FLASH */
	ldr	r3, _rel_dyn_end_ofs	/* r3 <- rel dyn end ofs */
	add	r3, r3, r0		/* r3 <- rel dyn end in FLASH */
fixloop:
	ldr	r0, [r2]		/* r0 <- location to fix up, IN FLASH! */
	add	r0, r0, r9		/* r0 <- location to fix up in RAM */
	ldr	r1, [r2, #4]
	and	r7, r1, #0xff
	cmp	r7, #23			/* relative fixup? */
	beq	fixrel
	cmp	r7, #2			/* absolute fixup? */
	beq	fixabs
	/* ignore unknown type of fixup */
	b	fixnext
fixabs:
	/* absolute fix: set location to (offset) symbol value */
	mov	r1, r1, LSR #4		/* r1 <- symbol index in .dynsym */
	add	r1, r10, r1		/* r1 <- address of symbol in table */
	ldr	r1, [r1, #4]		/* r1 <- symbol value */
	add	r1, r1, r9		/* r1 <- relocated sym addr */
	b	fixnext
fixrel:
	/* relative fix: increase location by offset */
	ldr	r1, [r0]
	add	r1, r1, r9
fixnext:
	str	r1, [r0]
	add	r2, r2, #8		/* each rel.dyn entry is 8 bytes */
	cmp	r2, r3
	blo	fixloop

clear_bss:  @清除_bss 段
	ldr	r0, _bss_start_ofs
	ldr	r1, _bss_end_ofs
	ldr	r3, _TEXT_BASE		/* Text base */
	mov	r4, r6			/* reloc addr */
	add	r0, r0, r4
	add	r1, r1, r4
	mov	r2, #0x00000000		/* clear			    */

clbss_l:str	r2, [r0]		/* clear loop...		    */
	add	r0, r0, #4
	cmp	r0, r1
	bne	clbss_l
#endif	/* #ifndef CONFIG_PRELOADER */

/*
 * We are done. Do not return, instead branch to second part of board
 * initialization, now running from RAM.
 */
 @初始化部分，从内存中開始执行
jump_2_ram:
	ldr	r0, _board_init_r_ofs
	adr	r1, _start
	add	lr, r0, r1
@	add	lr, lr, r9
	/* setup parameters for board_init_r */
	mov	r0, r5		/* gd_t */
	mov	r1, r6		/* dest_addr */
	/* jump to it ... */
	mov	pc, lr

_board_init_r_ofs:
	.word board_init_r - _start

_rel_dyn_start_ofs:
	.word __rel_dyn_start - _start
_rel_dyn_end_ofs:
	.word __rel_dyn_end - _start
_dynsym_start_ofs:
	.word __dynsym_start - _start

/*************************************************************************
 *
 * CPU_init_critical registers    CO=PU初始化控制錴
 *
 * setup important registers
 * setup memory timing
 *
 *************************************************************************/
cpu_init_crit:

	bl cache_init      @跳到缓存进行初始化

	/*
	 * Invalidate L1 I/D
	 */
	mov	r0, #0			@ set up for MCR
	mcr	p15, 0, r0, c8, c7, 0	@ invalidate TLBs    禁止TLB
	mcr	p15, 0, r0, c7, c5, 0	@ invalidate icache  禁止指令缓存

	/*
	 * disable MMU stuff and caches
	 */
	mrc	p15, 0, r0, c1, c0, 0
	bic	r0, r0, #0x00002000	@ clear bits 13 (--V-)
	bic	r0, r0, #0x00000007	@ clear bits 2:0 (-CAM)
	orr	r0, r0, #0x00000002	@ set bit 1 (--A-) Align
	orr	r0, r0, #0x00000800	@ set bit 12 (Z---) BTB
	mcr	p15, 0, r0, c1, c0, 0       @进制MMC和Cache

	/*
	 * Jump to board specific initialization...
	 * The Mask ROM will have already initialized
	 * basic memory. Go here to bump up clock rate and handle
	 * wake up conditions.
	 */
	mov	ip, lr			@ persevere link reg across call
	bl	lowlevel_init		@ go setup pll,mux,memory
	mov	lr, ip			@ restore link
	mov	pc, lr			@ back to my caller
/*
 *************************************************************************
 *
 * Interrupt handling   中断处理句柄
 *
 *************************************************************************
 */
@
@ 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

/*定义异常时保存寄存器的宏
 * 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		@ carve out a frame on current
						@ user stack
	stmia	sp, {r0 - r12}			@ Save user registers (now in
						@ svc mode) r0-r12
	ldr	r2, IRQ_STACK_START_IN		@ set base 2 words into abort
						@ stack
	ldmia	r2, {r2 - r3}			@ get values for "aborted" pc
						@ and cpsr (into parm regs)
	add	r0, sp, #S_FRAME_SIZE		@ grab pointer to old stack

	add	r5, sp, #S_SP
	mov	r1, lr
	stmia	r5, {r0 - r3}			@ save sp_SVC, lr_SVC, pc, cpsr
	mov	r0, sp				@ save current stack into r0
						@ (param register)
	.endm

	.macro	irq_save_user_regs
	sub	sp, sp, #S_FRAME_SIZE
	stmia	sp, {r0 - r12}			@ Calling r0-r12
	add	r8, sp, #S_PC			@ !! R8 NEEDS to be saved !!
						@ a reserved stack spot would
						@ be good.
	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, IRQ_STACK_START_IN		@ setup our mode stack (enter
						@ in banked mode)

	str	lr, [r13]			@ save caller lr in position 0
						@ of saved stack
	mrs	lr, spsr			@ get the spsr
	str	lr, [r13, #4]			@ save spsr in position 1 of
						@ saved stack

	mov	r13, #MODE_SVC			@ prepare SVC-Mode
	@ msr	spsr_c, r13
	msr	spsr, r13			@ switch modes, make sure
						@ moves will execute
	mov	lr, pc				@ capture return pc
	movs	pc, lr				@ jump to next instruction &
						@ switch modes.
	.endm

	.macro get_bad_stack_swi
	sub	r13, r13, #4			@ space on current stack for
						@ scratch reg.
	str	r0, [r13]			@ save R0's value.
	ldr	r0, IRQ_STACK_START_IN		@ get data regions start
						@ spots for abort stack
	str	lr, [r0]			@ save caller lr in position 0
						@ of saved stack
	mrs	r0, spsr			@ get the spsr
	str	lr, [r0, #4]			@ save spsr in position 1 of
						@ saved stack
	ldr	r0, [r13]			@ restore r0
	add	r13, r13, #4			@ pop stack entry
	.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   异常处理句柄
 */
	.align	5
undefined_instruction:
	get_bad_stack
	bad_save_user_regs
	bl	do_undefined_instruction

	.align	5
software_interrupt:
	get_bad_stack_swi
	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 effective 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