转：AM335x启动流程（BootRom->MLO->Uboot）

http://blog.chinaunix.net/uid-28458801-id-3486399.html

参考文件：

1，AM335x ARM Cortex-A8 Microprocessors (MPUs) Technical Reference Manual.pdf；

2，am3359.pdf；

1，am335x的cpu上电后，会跳到哪个地址去执行？

答：

芯片到uboot启动流程：ROM → MLO(SPL)→ uboot.img

AM335x 中bootloader被分成了 3 个部分：

第一级 bootloader：引导加载程序，板子上电后会自动执行这些代码，如选择哪种方式启动（NAND，SDcard，UART。。。），然后跳转转到第二级 bootloader。这些代码应该是存放在 176KB 的 ROM 中。

转：AM335x启动流程（BootRom->MLO->Uboot）

第二级 bootloader：MLO（SPL），用以硬件初始化：关闭看门狗，关闭中断，设置 CPU 时钟频率、速度等操作。然后会跳转到第三级bootloader。MLO文件应该会被映射到 64 KB的 Internal SRAM 中。

转：AM335x启动流程（BootRom->MLO->Uboot）

第三级 bootloader：uboot.img，C代码的入口。

转：AM335x启动流程（BootRom->MLO->Uboot）

其中第一级 bootloader 是板子固化的，第二级和第三级是通过编译 uboot 所得的。

转：AM335x启动流程（BootRom->MLO->Uboot）

2，第二级 bootloader：MLO（SPL）做了哪些事情？

MLO(SPL)内存分布如下：

SPL内存重映射：

< PATH : /arch/arm/cpu/armv7/omap-common/u-boot-spl.lds >

MEMORY { .sram : ORIGIN = CONFIG_SPL_TEXT_BASE,\

LENGTH = CONFIG_SPL_MAX_SIZE }

MEMORY { .sdram : ORIGIN = CONFIG_SPL_BSS_START_ADDR, \

LENGTH = CONFIG_SPL_BSS_MAX_SIZE }

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")

OUTPUT_ARCH(arm)

ENTRY(_start)

SECTIONS

{

.text :

{

__start = .;

arch/arm/cpu/armv7/start.o (.text)

*(.text*)

} >.sram

. = ALIGN(4);

.rodata : { *(SORT_BY_ALIGNMENT(.rodata*)) } >.sram

. = ALIGN(4);

.data : { *(SORT_BY_ALIGNMENT(.data*)) } >.sram

. = ALIGN(4);

__image_copy_end = .;

_end = .;

.bss :

{

. = ALIGN(4);

__bss_start = .;

*(.bss*)

. = ALIGN(4);

__bss_end__ = .;

} >.sdram

}

<PATH : /include/configs/am335x_evm.h>

#define CONFIG_SPL_TEXT_BASE 0x402F0400

#define CONFIG_SPL_MAX_SIZE (46 * 1024)

#define CONFIG_SPL_STACK LOW_LEVEL_SRAM_STACK

#define CONFIG_SPL_BSS_START_ADDR 0x80000000

#define CONFIG_SPL_BSS_MAX_SIZE     0x80000     /* 512 KB */ <span style="font-size:16px;color:#003399;"><strong></strong></span>

@1@ 保存启动参数 bl save_boot_params

<PATH : /arch/arm/cpu/armv7/start.S>

/*

* the actual reset code

*/

reset:

bl save_boot_params

<PATH : /arch/arm/cpu/armv7/omap-common/lowlevel_init.S>

.global save_boot_params

save_boot_params:

/*

* See if the rom code passed pointer is valid:

* It is not valid if it is not in non-secure SRAM

* This may happen if you are booting with the help of

* debugger

*/

ldr r2, =NON_SECURE_SRAM_START

cmp r2, r0

bgt 1f

ldr r2, =NON_SECURE_SRAM_END

cmp r2, r0

blt 1f

/*

* store the boot params passed from rom code or saved

* and passed by SPL

*/

cmp r0, #0

beq 1f

ldr r1, =boot_params

str r0, [r1]

/*《PATH: /arch/arm/include/asm/arch-ti81xx/omap.h》

* Non-secure SRAM Addresses

* Non-secure RAM starts at 0x40300000 for GP devices. But we keep SRAM_BASE

* at 0x40304000(EMU base) so that our code works for both EMU and GP

*/

#define NON_SECURE_SRAM_START 0x40304000

#define NON_SECURE_SRAM_END 0x4030E000

#define LOW_LEVEL_SRAM_STACK 0x4030B7FC

问题：这些参数是保存在哪里的？大概有哪些参数？

答：

这些参数保存的内存地址为 64 KB 的 OCM RAM 中：

转：AM335x启动流程（BootRom->MLO->Uboot）

注：Dowloaded Image 区域：是用来保存 MLO（SPL）文件的，其最大可达到 109 KB

转：AM335x启动流程（BootRom->MLO->Uboot）

@a2@ 设置 CPU 为 SVC32 模式

<PATH : /arch/arm/cpu/armv7/start.S>

/*

* set the cpu to SVC32 mode

*/

mrs r0, cpsr

bic r0, r0, #0x1f

orr r0, r0, #0xd3

msr cpsr,r0

CPSR:程序状态寄存器(current program status register)(当前程序状态寄存器)，在任何处理器模式下被访问。它包含了条件标志位、中断禁止位、当前处理器模式标志以及其他的一些控制和状态位。
CPSR在用户级编程时用于存储条件码。

SPSR:程序状态保存寄存器（saved program statusregister）,每一种处理器模式下都有一个状态寄存器SPSR,SPSR用于保存CPSR的状态，以便异常返回后恢复异常发生时的工作状态。当特定的异常中断发生时，这个寄存器用于存放当前程序状态寄存器的内容。在异常中断退出时，可以用SPSR来恢复CPSR。由于用户模式和系统模式不是异常中断模式，所以他没有SPSR。当用户在用户模式或系统模式访问SPSR，将产生不可预知的后果。

CPSR格式如下所示。SPSR和CPSR格式相同。
31 30 29 28 27 26 7 6 5 4 3 2 1 0
N Z C V Q DNM(RAZ) I F T M4 M3 M2 M1 M0

详解：http://blog.chinaunix.net/uid-28458801-id-3487199.html

@a3@ CPU的初始化

《PATH : /arch/arm/cpu/armv7/start.S》

/* the mask ROM code should have PLL and others stable */

#ifndef CONFIG_SKIP_LOWLEVEL_INIT

bl cpu_init_crit

#endif

<PATH : /arch/arm/cpu/armv7/omap-common/lowlevel_init.S>

.globl lowlevel_init

lowlevel_init:

/*

* Setup a temporary stack

*/

ldr sp, =LOW_LEVEL_SRAM_STACK

/*

* Save the old lr(passed in ip) and the current lr to stack

*/

push {ip, lr}

/*

* go setup pll, mux, memory

*/

bl s_init

pop {ip, pc}

问题：CPU的初始化有哪些内容？

答：

@b1@ 首先要设置堆栈区，因为将会调用 C函数来实现CPU的初始化

问题：这个堆栈在什么位置，其内存大小是多少？

答

1 2	`《PATH ：/arch/arm/include/asm/arch-ti81xx/omap.h》` `#define LOW_LEVEL_SRAM_STACK` `0x4030B7FC<strong></strong>`

转：AM335x启动流程（BootRom->MLO->Uboot）

@b2@ 执行 s_init() 函数，实现 CPU 的初始化

<PATH : /board/ti/am335x/evm.c>

/*

* 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();

/* Enable RTC32K clock */

rtc32k_enable();

/* UART softreset */

u32 regVal;

u32 uart_base = DEFAULT_UART_BASE;

enable_uart0_pin_mux();

/* 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();

preloader_console_init();

printf("\nlocation /board/ti/am335x\n"); //@@

/*@@*/

// led();

/*@@*/

config_am335x_ddr();

#endif

}

@c1@ 使能第二级缓冲区

/* Can be removed as A8 comes up with L2 enabled */

l2_cache_enable();

<PATH : /arch/arm/cpu/armv7/ti81xx/cache.S>

l2_cache_enable:

push {r0, r1, r2, lr}

mrc 15, 0, r3, cr1, cr0, 1

orr r3, r3, #2

mcr 15, 0, r3, cr1, cr0, 1

pop {r1, r2, r3, pc}

转：AM335x启动流程（BootRom->MLO->Uboot）

@c2@ 关闭看门狗（WDT）

/* 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);

<PATH : /arch/arm/include/asm/arch-ti81xx/cpu.h>

#define WDT_WSPR (WDT_BASE + 0x048)

<PATH : /arch/arm/include/asm/arch-ti81xx/hardware.h>

/* Watchdog Timer */

#ifdef CONFIG_AM335X

#define WDT_BASE 0x44E35000

#else

#define WDT_BASE 0x480C2000

#endif

@c3@ 给外设设置好 PLL 和时钟频率等

/* Setup the PLLs and the clocks for the peripherals */

pll_init();

<PATH : /board/ti/am335x/pll.c>

/*

* Configure the PLL/PRCM for necessary peripherals

*/

void pll_init()

{

mpu_pll_config(MPUPLL_M_500);

core_pll_config();

per_pll_config();

ddr_pll_config();

/* Enable the required interconnect clocks */

interface_clocks_enable();

/* Enable power domain transition */

power_domain_transition_enable();

/* Enable the required peripherals */

per_clocks_enable();

}

@c4@ 使能 32-KHz 频率的实时时钟

/* Enable RTC32K clock */

rtc32k_enable();

《PATH : /board/ti/am335x/evm.c》

static void rtc32k_enable(void)

{

/* Unlock the rtc's registers */

__raw_writel(0x83e70b13, (AM335X_RTC_BASE + RTC_KICK0_REG));

__raw_writel(0x95a4f1e0, (AM335X_RTC_BASE + RTC_KICK1_REG));

/* Enable the RTC 32K OSC */

__raw_writel(0x48, (AM335X_RTC_BASE + RTC_OSC_REG));

}

<PATH : /arch/arm/include/asm/arch-ti81xx/hardware.h>

/* RTC base address */

#define AM335X_RTC_BASE 0x44E3E000

<PATH : /board/ti/am335x/evm.c>

#define RTC_KICK0_REG 0x6c

#define RTC_KICK1_REG 0x70

#define RTC_OSC_REG 0x54

@c5@ 使能UART0

/* UART softreset */

u32 regVal;

u32 uart_base = DEFAULT_UART_BASE;

enable_uart0_pin_mux();

/* 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));

<PATH : /arch/arm/include/asm/arch-ti81xx/cpu.h>

#ifdef CONFIG_AM335X

#define DEFAULT_UART_BASE UART0_BASE

#endif

<PATH : /arch/arm/include/asm/arch-ti81xx/hardware.h>

#ifdef CONFIG_AM335X

#define UART0_BASE 0x44E09000

#else

#define UART0_BASE 0x48020000

#endif

转：AM335x启动流程（BootRom->MLO->Uboot）

@c6@ 初始化定时器

/* Initialize the Timer */

init_timer();

<PATH : /board/ti/am335x/evm.c>

static void init_timer(void)

{

/* Reset the Timer */

__raw_writel(0x2, (DM_TIMER2_BASE + TSICR_REG));

/* Wait until the reset is done */

while (__raw_readl(DM_TIMER2_BASE + TIOCP_CFG_REG) & 1);

/* Start the Timer */

__raw_writel(0x1, (DM_TIMER2_BASE + TCLR_REG));

}

<PATH : /arch/arm/include/asm/arch-ti81xx/hardware.h>

/* DM Timer base addresses */

#define DM_TIMER0_BASE 0x4802C000

#define DM_TIMER1_BASE 0x4802E000

#define DM_TIMER2_BASE 0x48040000

#define DM_TIMER3_BASE 0x48042000

#define DM_TIMER4_BASE 0x48044000

#define DM_TIMER5_BASE 0x48046000

#define DM_TIMER6_BASE 0x48048000

#define DM_TIMER7_BASE 0x4804A000

转：AM335x启动流程（BootRom->MLO->Uboot）

@c7@ 初始化控制台，通过UART可以查看相关信息

preloader_console_init();

《PATH : /arch/arm/cpu/armv7/omap-common/spl.c》

/* This requires UART clocks to be enabled */

void preloader_console_init(void)

{

const char *u_boot_rev = U_BOOT_VERSION;

char rev_string_buffer[50];

gd = &gdata;

gd->bd = &bdata;

gd->flags |= GD_FLG_RELOC;

gd->baudrate = CONFIG_BAUDRATE;

serial_init(); /* serial communications setup */

/* Avoid a second "U-Boot" coming from this string */

u_boot_rev = &u_boot_rev[7];

printf("\nU-Boot SPL %s (%s - %s)\n", u_boot_rev, U_BOOT_DATE,

U_BOOT_TIME);

omap_rev_string(rev_string_buffer);

printf("Texas Instruments %s\n", rev_string_buffer);

} <span style="font-size:14px;color:#003399;"></span>

@c8@ 配置 DDR

config_am335x_ddr();

《PATH ：》

/* void DDR2_EMIF_Config(void); */

static void config_am335x_ddr(void)

{

int data_macro_0 = 0;

int data_macro_1 = 1;

enable_ddr_clocks();

config_vtp();

Cmd_Macro_Config();

Data_Macro_Config(data_macro_0);

Data_Macro_Config(data_macro_1);

__raw_writel(PHY_RANK0_DELAY, DATA0_RANK0_DELAYS_0);

__raw_writel(PHY_RANK0_DELAY, DATA1_RANK0_DELAYS_0);

__raw_writel(DDR_IOCTRL_VALUE, DDR_CMD0_IOCTRL);

__raw_writel(DDR_IOCTRL_VALUE, DDR_CMD1_IOCTRL);

__raw_writel(DDR_IOCTRL_VALUE, DDR_CMD2_IOCTRL);

__raw_writel(DDR_IOCTRL_VALUE, DDR_DATA0_IOCTRL);

__raw_writel(DDR_IOCTRL_VALUE, DDR_DATA1_IOCTRL);

__raw_writel(__raw_readl(DDR_IO_CTRL) & 0xefffffff, DDR_IO_CTRL);

__raw_writel(__raw_readl(DDR_CKE_CTRL) | 0x00000001, DDR_CKE_CTRL);

config_emif_ddr2();

}

《PATH : /arm/include/asm/arch-ti81xx/cpu.h》

#define DATA0_RANK0_DELAYS_0 (DDR_PHY_BASE_ADDR + 0x134)

#define DATA1_RANK0_DELAYS_0 (DDR_PHY_BASE_ADDR + 0x1D8)

/* DDR offsets */

#define DDR_PHY_BASE_ADDR 0x44E12000

#define DDR_IO_CTRL 0x44E10E04

#define DDR_CKE_CTRL 0x44E1131C

#define CONTROL_BASE_ADDR 0x44E10000

转：AM335x启动流程（BootRom->MLO->Uboot）

@c DONE@

@b DONE@

@a4@ 设置 internal RAM 内存空间的栈指针，调用 board_init_f()函数

/* 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

<PATH: include/configs/am335x_evm.h>

#define CONFIG_SYS_INIT_SP_ADDR (CONFIG_SYS_INIT_RAM_ADDR + \

CONFIG_SYS_INIT_RAM_SIZE - \

GENERATED_GBL_DATA_SIZE)

#define CONFIG_SYS_INIT_RAM_ADDR SRAM0_START

#define CONFIG_SYS_INIT_RAM_SIZE SRAM0_SIZE

<PATH : /arch/arm/include/asm/arch-ti81xx/hardware.h : begin>

#ifdef CONFIG_AM335X

#define SRAM0_START 0x402F0400

#else

#define SRAM0_START 0x40300000

#endif

<PATH : /arch/arm/include/asm/arch-ti81xx/hardware.h : end>

<PATH : /arch/arm/include/asm/arch-ti81xx/cpu.h : begin>

#if defined(CONFIG_AM335X) || defined(CONFIG_TI814X)

#define SRAM0_SIZE (0x1B400) /* 109 KB */

#define SRAM_GPMC_STACK_SIZE (0x40)

#endif

<PATH : /arch/arm/include/asm/arch-ti81xx/cpu.h : end>

<PATH : /am335x/include/generated/generic-asm-offsets.h : begin>

#define GENERATED_GBL_DATA_SIZE (128) /* (sizeof(struct global_data) + 15) & ~15 */

<PATH : /am335x/include/generated/generic-asm-offsets.h : end>

<PATH : /arch/arm/cpu/armv7/omap-common/spl.c'>

void board_init_f(ulong dummy)

{

/*

* We call relocate_code() with relocation target same as the

* CONFIG_SYS_SPL_TEXT_BASE. This will result in relocation getting

* skipped. Instead, only .bss initialization will happen. That's

* all we need

*/

debug(">>board_init_f()\n");

relocate_code(CONFIG_SPL_STACK, &gdata, CONFIG_SPL_TEXT_BASE);

}

<PATH : /arch/arm/cpu/armv7/omap-common/spl.c : begin>

#define CONFIG_SPL_TEXT_BASE 0x402F0400

#define CONFIG_SPL_MAX_SIZE (46 * 1024)

#define CONFIG_SPL_STACK LOW_LEVEL_SRAM_STACK

<PATH : /arch/arm/cpu/armv7/omap-common/spl.c : end>

<PATH : /arch/arm/include/asm/arch-ti81xx/omap.h : begin>

#define LOW_LEVEL_SRAM_STACK 0x4030B7FC

<PATH : /arch/arm/include/asm/arch-ti81xx/omap.h : end>

<PATH : /arch/arm/cpu/armv7/start.S>

/*

* 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 0x402F0400*/

@a5@ 代码重定位

代码重定向，它首先检测自己(MLO)是否已经在内存中：

如果是直接跳到下面的堆栈初始化代码 clear_bss。

如果不是就将自己从Nor Flash中拷贝到内存中。

Nor Flash 和Nand Flash 本质区别就在于是否进行代码拷贝，也就是下面代码所表述：无论
是Nor Flash 还是Nand Flash，核心思想就是将 uboot 代码搬运到内存中去运行，但是没有拷
贝bss 后面这段代码，只拷贝bss 前面的代码，bss 代码是放置全局变量的。Bss 段代码是为
了清零，拷贝过去再清零重复操作。

/* 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: /* 自拷贝 */

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

@a6@ 清空 bss 段

clear_bss:

ldr r0, _bss_start_ofs

ldr r1, _bss_end_ofs

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

/*

* These are defined in the board-specific linker script.

*/

.globl _bss_start_ofs

_bss_start_ofs:

.word __bss_start - _start /* __bss_start = 0x80000000 */

@a7@ 调用函数 board_init_r，用以完成 MLO（SPI）阶段的所有初始化，并跳转到 uboot.img 阶段

/*

* 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

_board_init_r_ofs:

.word board_init_r - _start

《PATH : /arch/arm/cpu/armv7/omap-common/spl.c 》

void board_init_r(gd_t *id, ulong dummy)

{

u32 boot_device;

debug(">>spl:board_init_r()\n");

timer_init();

i2c_init(CONFIG_SYS_I2C_SPEED, CONFIG_SYS_I2C_SLAVE);

#ifdef CONFIG_SPL_BOARD_INIT

spl_board_init();

#endif

boot_device = omap_boot_device();

debug("boot device - %d\n", boot_device);

switch (boot_device) {

#ifdef CONFIG_SPL_MMC_SUPPORT

case BOOT_DEVICE_MMC1:

case BOOT_DEVICE_MMC2:

spl_mmc_load_image();

break;

#endif

#ifdef CONFIG_SPL_NAND_SUPPORT

case BOOT_DEVICE_NAND:

spl_nand_load_image();

break;

#endif

#ifdef CONFIG_SPL_YMODEM_SUPPORT

case BOOT_DEVICE_UART:

spl_ymodem_load_image();

break;

#endif

default:

printf("SPL: Un-supported Boot Device - %d!!!\n", boot_device);

hang();

break;

}

switch (spl_image.os) {

case IH_OS_U_BOOT:

debug("Jumping to U-Boot\n");

jump_to_image_no_args();

break;

default:

puts("Unsupported OS image.. Jumping nevertheless..\n");

jump_to_image_no_args();

}

@a DONE@

3，第三级 bootloader：uboot.img 做了哪些事情？

uboot.img 内存分布如下：

转：AM335x启动流程（BootRom->MLO->Uboot）

访问 /arch/arm/lib/board.c 中 的 board_init_f() 函数：

在 uboot.img 运行过程中，有两个非常重要的结构体：gd_t 和 bd_t 。

其中 gd_t ：global_data 数据结构的定义，位于：/arch/arm/include/asm/global_data.h 中。

其成员主要是一些全局的系统初始化参数。

其中 bd_t ：bd_info 数据结构的定义，位于：/arch/arm/include/asm/u-boot.h 中。

其成员是开发板的相关参数。

<PATH : /arch/arm/include/asm/global_data.h >

/*

* The following data structure is placed in some memory which is

* available very early after boot (like DPRAM on MPC8xx/MPC82xx, or

* some locked parts of the data cache) to allow for a minimum set of

* global variables during system initialization (until we have set

* up the memory controller so that we can use RAM).

*

* Keep it *SMALL* and remember to set GENERATED_GBL_DATA_SIZE > sizeof(gd_t)

*/

typedef struct global_data {

bd_t *bd;

unsigned long flags;

unsigned long baudrate;

unsigned long have_console; /* serial_init() was called */

unsigned long env_addr; /* Address of Environment struct */

unsigned long env_valid; /* Checksum of Environment valid? */

unsigned long fb_base; /* base address of frame buffer */

#ifdef CONFIG_FSL_ESDHC

unsigned long sdhc_clk;

#endif

#ifdef CONFIG_AT91FAMILY

/* "static data" needed by at91's clock.c */

unsigned long cpu_clk_rate_hz;

unsigned long main_clk_rate_hz;

unsigned long mck_rate_hz;

unsigned long plla_rate_hz;

unsigned long pllb_rate_hz;

unsigned long at91_pllb_usb_init;

#endif

#ifdef CONFIG_ARM

/* "static data" needed by most of timer.c on ARM platforms */

unsigned long timer_rate_hz;

unsigned long tbl;

unsigned long tbu;

unsigned long long timer_reset_value;

unsigned long lastinc;

#endif

#ifdef CONFIG_IXP425

unsigned long timestamp;

#endif

unsigned long relocaddr; /* Start address of U-Boot in RAM */

phys_size_t ram_size; /* RAM size */

unsigned long mon_len; /* monitor len */

unsigned long irq_sp; /* irq stack pointer */

unsigned long start_addr_sp; /* start_addr_stackpointer */

unsigned long reloc_off;

#if !(defined(CONFIG_SYS_ICACHE_OFF) && defined(CONFIG_SYS_DCACHE_OFF))

unsigned long tlb_addr;

#endif

void **jt; /* jump table */

char env_buf[32]; /* buffer for getenv() before reloc. */

} gd_t;

#define DECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("r8")

<PATH : /arch/arm/include/asm/u-boot.h >

typedef struct bd_info {

int bi_baudrate; /* serial console baudrate */

unsigned long bi_ip_addr; /* IP Address */

ulong bi_arch_number; /* unique id for this board */

ulong bi_boot_params; /* where this board expects params */

struct /* RAM configuration */

{

ulong start;

ulong size;

} bi_dram[CONFIG_NR_DRAM_BANKS];

} bd_t;

其中 DECLARE_GLOBAL_DATA_PTR 宏定义在系统初始化过程中会被频繁调用，

其的作用是，声明gd这么一个全局的指针，这个指针指向gd_t结构体类型，并且这个gd指针是保存在ARM的r8这个寄存器里面的。

uboot.img 第一个运行的文件还是 start.o，其在运行访问的 board_init_f() 函数定义在 /arch/arm/lib/board.c 中：

<PATH : /arch/arm/lib/board.c >

void board_init_f(ulong bootflag)

{

bd_t *bd;

init_fnc_t **init_fnc_ptr;

gd_t *id;

ulong addr, addr_sp;

/* Pointer is writable since we allocated a register for it */

gd = (gd_t *) ((CONFIG_SYS_INIT_SP_ADDR) & ~0x07);

/* compiler optimization barrier needed for GCC >= 3.4 */

__asm__ __volatile__("": : :"memory");

memset((void *)gd, 0, sizeof(gd_t));

...

}

<PATH : /include/configs/am335x_evm>

#define CONFIG_SYS_INIT_RAM_ADDR SRAM0_START

#define CONFIG_SYS_INIT_RAM_SIZE SRAM0_SIZE

#define CONFIG_SYS_INIT_SP_ADDR (CONFIG_SYS_INIT_RAM_ADDR + \

CONFIG_SYS_INIT_RAM_SIZE - \

GENERATED_GBL_DATA_SIZE)

<PATH : /arch/arm/include/asm/arch-ti81xx/hardware.h>

#define SRAM0_START 0x402F0400

<PATH : /arch/arm/include/asm/arch-ti81xx/cpu.h>

#define SRAM0_SIZE (0x1B400) /* 109 KB */

<PATH : /am335x/include/generated/generic-asm-offsets.h>

#define GENERATED_GBL_DATA_SIZE (128) /* (sizeof(struct global_data) + 15) & ~15 */

因此，系统初始化参数将会被保存在（保存 MLO（SPL）文件的内存空间的）末尾 2 KB 处。

通过计算的 gb 指针指向的内存空间地址为 gb = 0x4030B000

转：AM335x启动流程（BootRom->MLO->Uboot）

gb_t 结构体中某些元素的值是来自于 uboot.img's header，这个header的数据保存在内存的0x807FFFCO，大小为 64字节

<PATH : /include/image.h>

/*

* Legacy format image header,

* all data in network byte order (aka natural aka bigendian).

*/

typedef struct image_header {

uint32_t ih_magic; /* Image Header Magic Number */

uint32_t ih_hcrc; /* Image Header CRC Checksum */

uint32_t ih_time; /* Image Creation Timestamp */

uint32_t ih_size; /* Image Data Size */

uint32_t ih_load; /* Data Load Address */

uint32_t ih_ep; /* Entry Point Address */

uint32_t ih_dcrc; /* Image Data CRC Checksum */

uint8_t ih_os; /* Operating System */

uint8_t ih_arch; /* CPU architecture */

uint8_t ih_type; /* Image Type */

uint8_t ih_comp; /* Compression Type */

uint8_t ih_name[IH_NMLEN]; /* Image Name */

} image_header_t;

<PATH : /include/configs/am335x_evm.h>

/*

* 8MB into the SDRAM to allow for SPL's bss at the beginning of SDRAM.

* 64 bytes before this address should be set aside for u-boot.img's

* header. That is 0x807FFFC0--0x80800000 should not be used for any

* other needs.

*/

#define CONFIG_SYS_TEXT_BASE 0x80800000

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转：AM335x启动流程（BootRom->MLO->Uboot）

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