基于devkit8600的2011.04版uboot启动代码Start.s分析
/*
* armboot - Startup Code for OMAP3530/ARM Cortex CPU-core
*
* Copyright (c) 2004 Texas Instruments <r-woodruff2@ti.com>
*
* Copyright (c) 2001 Marius Gröger <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> .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
#ifdef CONFIG_SPL_BUILD
_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
_pad: .word 0x12345678 /* now 16*4=64 */
#else
_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
_pad: .word 0x12345678 /* now 16*4=64 */
#endif /* CONFIG_SPL_BUILD */ .global _end_vect
_end_vect: .balignl 16,0xdeadbeef
/*************************************************************************
*
* Startup Code (reset vector)
*
* 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 #ifdef CONFIG_TEGRA2
/*
* Tegra2 uses 2 separate CPUs - the AVP (ARM7TDMI) and the CPU (dual A9s).
* U-Boot runs on the AVP first, setting things up for the CPU (PLLs,
* muxes, clocks, clamps, etc.). Then the AVP halts, and expects the CPU
* to pick up its reset vector, which points here.
*/
.globl _armboot_start
_armboot_start:
.word _start
#endif /*
* These are defined in the board-specific linker script.
*/
.globl _bss_start_ofs
_bss_start_ofs:
.word __bss_start - _start .global _image_copy_end_ofs
_image_copy_end_ofs:
.word __image_copy_end - _start .globl _bss_end_ofs
_bss_end_ofs:
.word __bss_end__ - _start .globl _end_ofs
_end_ofs:
.word _end - _start #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 /* IRQ stack memory (calculated at run-time) + 8 bytes */
.globl IRQ_STACK_START_IN
IRQ_STACK_START_IN:
.word 0x0badc0de /*
* the actual reset code
*/ reset:
bl save_boot_params
/**************************************************************************/
save_boot_params
在arch/arm/cpu/armv7/cpu.c中定义
在arch/arm/cpu/armv7/ti81xx/lowlevel_init.s中生重定义
/**************************************************************************/
/*
* set the cpu to SVC32 mode
*/
mrs r0, cpsr
bic r0, r0, #0x1f
orr r0, r0, #0xd3
msr cpsr,r0 #if defined(CONFIG_OMAP34XX)
/* Copy vectors to mask ROM indirect addr */
adr r0, _start @ r0 <- current position of code
add r0, r0, #4 @ skip reset vector
mov r2, #64 @ r2 <- size to copy
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.
*/
bl cpy_clk_code @ put dpll adjust code behind vectors
#endif /* NAND Boot */
#endif
/* the mask ROM code should have PLL and others stable */ #ifndef CONFIG_SKIP_LOWLEVEL_INIT
bl cpu_init_crit
/**************************************************************************/
cpu_init_crit在本文件中定义
/**************************************************************************/
#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 /*------------------------------------------------------------------------------*/
/**************************************************************************/
board_init_f在arch/arm/lib/board.c中定义,
/**************************************************************************/
/*
* 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:
/**************************************************************************/
relocate_code由board_init_f返回，它的作用是初始化栈、清零bss段，之后跳到board_init_r，
并将
给gd指针和u-boot代码段地址()作为参数传进去
/**************************************************************************/
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
cmp r0, r6
moveq r9, #0 /* no relocation. relocation offset(r9) = 0 */
beq clear_bss /* skip relocation */
mov r1, r6 /* r1 <- scratch for copy_loop */
ldr r3, _image_copy_end_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_SPL_BUILD
/*
* 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
b clear_bss
_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 #endif /* #ifndef CONFIG_SPL_BUILD */ clear_bss:
#ifdef CONFIG_SPL_BUILD
/* No relocation for SPL */
ldr r0, =__bss_start
ldr r1, =__bss_end__
#else
ldr r0, _bss_start_ofs
ldr r1, _bss_end_ofs
mov r4, r6 /* reloc addr */
add r0, r0, r4
add r1, r1, r4
#endif
mov r2, #0x00000000 /* clear */ clbss_l:str r2, [r0] /* clear loop... */
add r0, r0, #4
cmp r0, r1
bne clbss_l /*
* We are done. Do not return, instead branch to second part of board
* initialization, now running from RAM.
*/
jump_2_ram:
/*
* If I-cache is enabled invalidate it
*/
#ifndef CONFIG_SYS_ICACHE_OFF
mcr p15, 0, r0, c7, c5, 0 @ invalidate icache
mcr p15, 0, r0, c7, c10, 4 @ DSB
mcr p15, 0, r0, c7, c5, 4 @ ISB
#endif
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
/**************************************************************************/
跳到board_init_r，它在arch/arm/lib/board.c中定义,其中：
LDR R0，Label 将程序标号地址连续的4个字节（1个字）的数据传送到目的寄存器中
ADR R0, _start把 _start地址读出来，而且这个地址是相对当前pc的，所以和当前程序运行地址相关,r0是代码的当前位置
ldr r0, _board_init_r_ofs //r0=board_init_r - _start(board_init_r偏移地址)
adr r1, _start //r1=_start的运行地址
add lr, r0, r1 //lr=board_init_r的真正运行地址
add lr, lr, r9 //r9保存重定向偏移大小，spl中 r9 = 0
mov r0, r5 //r0 = &gdata
mov r1, r6 //r6=CONFIG_SPL_TEXT_BASE
mov pc, lr //跳转到board_init_r
/**************************************************************************/
_board_init_r_ofs:
.word board_init_r - _start #ifndef CONFIG_SKIP_LOWLEVEL_INIT
/*************************************************************************
*
* CPU_init_critical registers
*
* setup important registers
* setup memory timing
*
*************************************************************************/
cpu_init_crit:
/*
* Invalidate L1 I/D
*/
mov r0, #0 @ set up for MCR
mcr p15, 0, r0, c8, c7, 0 @ invalidate TLBs
mcr p15, 0, r0, c7, c5, 0 @ invalidate icache
mcr p15, 0, r0, c7, c5, 6 @ invalidate BP array
mcr p15, 0, r0, c7, c10, 4 @ DSB
mcr p15, 0, r0, c7, c5, 4 @ ISB /*
* 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 11 (Z---) BTB
#ifdef CONFIG_SYS_ICACHE_OFF
bic r0, r0, #0x00001000 @ clear bit 12 (I) I-cache
#else
orr r0, r0, #0x00001000 @ set bit 12 (I) I-cache
#endif
mcr p15, 0, r0, c1, c0, 0 /*
* 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
/**************************************************************************/
lowlevel_init在arch/arm/cpu/armv7/ti81xx/lowlevel_init.s中定义
/**************************************************************************/
mov lr, ip @ restore link
mov pc, lr @ back to my caller
#endif #ifndef CONFIG_SPL_BUILD
/*
*************************************************************************
*
* 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 @ 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
*/
.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 /* CONFIG_USE_IRQ */
#endif /* CONFIG_SPL_BUILD */
/*****************************************************************************
* lowlevel_init: - Platform low level init.
* Corrupted Register : r0, r1, r2, r3, r4, r5, r6
****************************************************************************/
.globl lowlevel_init
lowlevel_init: /* The link register is saved in ip by start.S */
mov r6, ip
/* check if we are already running from RAM */
ldr r2, _lowlevel_init
ldr r3, _TEXT_BASE
sub r4, r2, r3
sub r0, pc, r4
/* require dummy instr or subtract pc by 4 instead i'm doing stack init */
ldr sp, SRAM_STACK
mark1:
ldr r5, _mark1
sub r5, r5, r2 /* bytes between mark1 and lowlevel_init */
sub r0, r0, r5 /* r0 <- _start w.r.t current place of execution */
mov r10, #0x0 /* r10 has in_ddr used by s_init() */ #ifdef CONFIG_NOR_BOOT
cmp r0, #0x08000000 /* check for running from NOR */
beq ocmc_init_start /* if == then running from NOR */
ands r0, r0, #0xC0000000 /* MSB 2 bits <> 0 then we are in ocmc or DDR */
cmp r0, #0x40000000 /* if running from ocmc */
beq nor_init_start /* if == skip ocmc init and jump to nor init */
mov r10, #0x01 /* if <> we are running from DDR hence skip ddr init */
/* by setting in_ddr to 1 */
b s_init_start /* and jump to s_init */
/**************************************************************************/
s_init_start在本源代最后部分定义
/**************************************************************************/
#else
ands r0, r0, #0xC0000000 /* MSB 2 bits <> 0 then we are in ocmc or DDR */
cmp r0, #0x80000000
bne s_init_start
mov r10, #0x01
b s_init_start
#endif #ifdef CONFIG_NOR_BOOT
ocmc_init_start:
/**** enable ocmc 0 ****/
/* CLKSTCTRL */
ldr r5, cm_alwon_ocmc_0_clkstctrl_addr
mov r2, #0x2
str r2, [r5]
/* wait for gpmc enable to settle */
ocmc0_wait0:
ldr r2, [r5]
#ifdef CONFIG_AM335X
ands r2, r2, #0x00000100
cmp r2, #0x00000100
#else
ands r2, r2, #0x00000010
cmp r2, #0x00000010
#endif
bne ocmc0_wait0
/* CLKCTRL */
ldr r5, cm_alwon_ocmc_0_clkctrl_addr
mov r2, #0x2
str r2, [r5]
/* wait for gpmc enable to settle */
ocmc0_wait1:
ldr r2, [r5]
ands r2, r2, #0x00030000
cmp r2, #0
bne ocmc0_wait1 #ifndef CONFIG_AM335X
/**** enable ocmc 1 ****/
/* CLKSTCTRL */
ldr r5, cm_alwon_ocmc_1_clkstctrl_addr
mov r2, #0x2
str r2, [r5]
/* wait for gpmc enable to settle */
ocmc1_wait0:
ldr r2, [r5]
ands r2, r2, #0x00000100
cmp r2, #0x00000100
bne ocmc1_wait0
/* CLKCTRL */
ldr r5, cm_alwon_ocmc_1_clkctrl_addr
mov r2, #0x2
str r2, [r5]
/* wait for gpmc enable to settle */
ocmc1_wait1:
ldr r2, [r5]
ands r2, r2, #0x00030000
cmp r2, #0
bne ocmc1_wait1
#endif
nor_init_start:
/* gpmc init */
bl cpy_nor_gpmc_code /* copy nor gpmc init code to sram */
mov r0, pc
add r0, r0, #12 /* 12 is for next three instructions */
mov lr, r0 /* gpmc init code in sram should return to s_init_start */
ldr r0, sram_pc_start
mov pc, r0 /* transfer ctrl to nor_gpmc_init() in sram */
#endif s_init_start:
mov r0, r10 /* passing in_ddr in r0 */
bl s_init
/**************************************************************************/
s_init在board/embest/devkit8600/evm.c中定义,
/**************************************************************************/
/* back to arch calling code */
mov pc, r6
/* the literal pools origin */
.ltorg #ifdef CONFIG_NOR_BOOT
cm_alwon_ocmc_0_clkstctrl_addr:
.word CM_ALWON_OCMC_0_CLKSTCTRL
cm_alwon_ocmc_0_clkctrl_addr:
.word CM_ALWON_OCMC_0_CLKCTRL
#ifndef CONFIG_AM335X
cm_alwon_ocmc_1_clkstctrl_addr:
.word CM_ALWON_OCMC_1_CLKSTCTRL
cm_alwon_ocmc_1_clkctrl_addr:
.word CM_ALWON_OCMC_1_CLKCTRL
#endif
#endif
SRAM_STACK:
.word LOW_LEVEL_SRAM_STACK _mark1:
.word mark1
_lowlevel_init:
.word lowlevel_init
_s_init_start:
.word s_init_start
/*
* early system init of muxing and clocks.
*/
void s_init(void)
{
/* Can be removed as A8 comes up with L2 enabled */
l2_cache_enable(); /* WDT1 is already running when the bootloader gets control
* Disable it to avoid "random" resets
*/
__raw_writel(0xAAAA, WDT_WSPR);
while(__raw_readl(WDT_WWPS) != 0x0);
__raw_writel(0x5555, WDT_WSPR);
while(__raw_readl(WDT_WWPS) != 0x0); #ifdef CONFIG_SPL_BUILD
/* Setup the PLLs and the clocks for the peripherals */
pll_init();
/**************************************************************************/
pll_init在board/embest/devkit8600/pll.c中定义
/**************************************************************************/
/* UART softreset */
u32 regVal;
u32 uart_base = DEFAULT_UART_BASE; enable_uart0_pin_mux();
/**************************************************************************/
enable_uart0_pin_mux在board/embest/devkit8600/mux.c中定义
/**************************************************************************/
/* IA Motor Control Board has default console on UART3*/
/* XXX: This is before we've probed / set board_id */
if (board_id == IA_BOARD) {
uart_base = UART3_BASE;
} regVal = __raw_readl(uart_base + UART_SYSCFG_OFFSET);
regVal |= UART_RESET;
__raw_writel(regVal, (uart_base + UART_SYSCFG_OFFSET) );
while ((__raw_readl(uart_base + UART_SYSSTS_OFFSET) &
UART_CLK_RUNNING_MASK) != UART_CLK_RUNNING_MASK); /* Disable smart idle */
regVal = __raw_readl((uart_base + UART_SYSCFG_OFFSET));
regVal |= UART_SMART_IDLE_EN;
__raw_writel(regVal, (uart_base + UART_SYSCFG_OFFSET)); /* Initialize the Timer */
init_timer();
/**************************************************************************/
init_timer在本源码文件中定义
/**************************************************************************/
preloader_console_init();
/**************************************************************************/
preloader_console_init在arch/arm/cpu/armv7/omap-common/spl.c中定义
uboot启动时，打印的第一个信息，就是它打印的
/**************************************************************************/
config_am335x_ddr();
/**************************************************************************/
enable_uart0_pin_mux在本源码文件中定义
/**************************************************************************/
#endif
}
参考：
1 [UBOOT] AM335x 启动流程（u-boot-2011.09）
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