AM335x启动流程（BootRom->MLO->Uboot）

kenson · 发表于 2017-3-21 22:26

本帖最后由 kenson 于 2017-3-21 22:36 编辑

http://blog.csdn.net/psvoldemort/article/details/41861959

kenson · 发表于 2017-3-22 08:39

本帖最后由 kenson 于 2017-3-22 09:26 编辑

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。

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。

第三级 bootloader：uboot.img，C代码的入口。

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。

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：

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< 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
}

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#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 */

@1@ 保存启动参数 bl save_boot_params

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/*
* the actual reset code
*/

reset:
bl save_boot_params

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.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]

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/*《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：

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

@a2@ 设置 CPU 为 SVC32 模式

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      /*
   * 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

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《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

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.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
3 s1 H" u) i% a. J: _5 w

问题：这个堆栈在什么位置，其内存大小是多少？

答

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《PATH ：/arch/arm/include/asm/arch-ti81xx/omap.h》
#define LOW_LEVEL_SRAM_STACK 0x4030B7FC

& S- G4 U6 C0 Y

@b2@ 执行 s_init() 函数，实现 CPU 的初始化

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/*
* 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("location /board/ti/am335x");       //@@
/*@@*/
//  led();
/*@@*/

config_am335x_ddr();

#endif
}

@c1@ 使能第二级缓冲区

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/* Can be removed as A8 comes up with L2 enabled */
l2_cache_enable();

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}

@c2@ 关闭看门狗（WDT）* y `4 g8 V' m) U2 F6 h

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/* 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);

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#define WDT_WSPR (WDT_BASE + 0x048)

/* Watchdog Timer */
#ifdef CONFIG_AM335X
#define WDT_BASE 0x44E35000
#else
#define WDT_BASE 0x480C2000
#endif

9 V% r" p& x; }+ s6 O4 h

@c3@ 给外设设置好 PLL 和时钟频率等

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/* Setup the PLLs and the clocks for the peripherals */
pll_init();

/*
* 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();
}

$ D' K' `1 K& ~$ U

@c4@ 使能 32-KHz 频率的实时时钟

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/* 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));
}

/* RTC base address */
#define AM335X_RTC_BASE          0x44E3E000

#define RTC_KICK0_REG       0x6c
#define RTC_KICK1_REG       0x70
#define RTC_OSC_REG       0x54

@c5@ 使能UART0

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/* 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));

#ifdef CONFIG_AM335X
#define DEFAULT_UART_BASE    UART0_BASE
#endif

#ifdef CONFIG_AM335X
#define UART0_BASE       0x44E09000
#else
#define UART0_BASE       0x48020000
#endif

@c6@ 初始化定时器

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/* Initialize the Timer */
init_timer();

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));
}

/* 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

@c7@ 初始化控制台，通过UART可以查看相关信息

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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("U-Boot SPL %s (%s - %s)", u_boot_rev, U_BOOT_DATE,
U_BOOT_TIME);
omap_rev_string(rev_string_buffer);
printf("Texas Instruments %s", rev_string_buffer);
}

@c8@ 配置 DDR

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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

@c DONE@

@b DONE@

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

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/* 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

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#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

#ifdef CONFIG_AM335X
#define SRAM0_START       0x402F0400
#else
#define SRAM0_START       0x40300000
#endif

#if defined(CONFIG_AM335X) || defined(CONFIG_TI814X)
#define SRAM0_SIZE       (0x1B400) /* 109 KB */
#define SRAM_GPMC_STACK_SIZE       (0x40)
#endif

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

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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()");
relocate_code(CONFIG_SPL_STACK, &gdata, CONFIG_SPL_TEXT_BASE);
}

#define CONFIG_SPL_TEXT_BASE       0x402F0400
#define CONFIG_SPL_MAX_SIZE    (46 * 1024)
#define CONFIG_SPL_STACK       LOW_LEVEL_SRAM_STACK

#define LOW_LEVEL_SRAM_STACK 0x4030B7FC

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/*
* 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" C* ]$ p1 x6 p- x0 e7 [
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3 f* ^! V! t& [5 {1 x: M
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# Z; S- n0 Q2 H: e" ~( w7 X5 }9 r E
了清零，拷贝过去再清零重复操作。0 A* ^' [5 @4 j! B* t

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/* 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

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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

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/*
* 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

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《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()");

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", 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!!!", boot_device);
      hang();
      break;
}

switch (spl_image.os) {
case IH_OS_U_BOOT:
      debug("Jumping to U-Boot");
      jump_to_image_no_args();
      break;
default:
      puts("Unsupported OS image.. Jumping nevertheless..");
      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：

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。

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/*
* 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")

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：

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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));

...
}

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#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)

#define SRAM0_START       0x402F0400

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

#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

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

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/*
* 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;

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/*
* 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

zhixiaoyuhong · 发表于 2017-3-23 08:27

ti的这款片子确实不错，国外特别火，楼主，我们搞底层的搞这么细有用吗？我总感觉我们这碗饭越来越难吃了。。。

kenson · 发表于 2017-3-23 09:45

zhixiaoyuhong 发表于 2017-3-23 08:27
* i q) w' X& R1 n8 iti的这款片子确实不错，国外特别火，楼主，我们搞底层的搞这么细有用吗？我总感觉我们这碗饭越来越难吃了。 ...

其实我也不想搞那么深入的，但不搞深入心里也不踏实，现在市面上好多相当便宜的芯片，虽然好多帮你移植好的如uboot linux但个别也有半成品，有时候想修改它的uboot参数这就没办法了，手上也有单子要用到这TI芯片，虽然买回来人家帮你搞好了底层，但公司名字都在里面都要改的，
如果只搞应用层那就不必要去搞这么底层，如果想搞明白来龙去脉那只能这样子了。

zhixiaoyuhong · 发表于 2017-3-24 08:20

kenson 发表于 2017-3-23 09:45
: ^+ a' N* j0 o/ n7 e其实我也不想搞那么深入的，但不搞深入心里也不踏实，现在市面上好多相当便宜的芯片，虽然好多帮你移植好 ...

现在板子这么便宜，配置也不错，好羡慕人家搞应用的，随便花百八十块钱，买块板子，就可以搞应用，玩的很转。。。

kenson · 发表于 2017-3-24 08:31

zhixiaoyuhong 发表于 2017-3-24 08:20
- p5 f: w) a# d( y现在板子这么便宜，配置也不错，好羡慕人家搞应用的，随便花百八十块钱，买块板子，就可以搞应用，玩的很 ...

没必要羡慕人家的,别人也是要经过这个阶段的,当然你也可以。

zhixiaoyuhong · 发表于 2017-3-24 08:57

kenson 发表于 2017-3-24 08:31
, _) s" B& K/ A% P! M2 `没必要羡慕人家的,别人也是要经过这个阶段的,当然你也可以。

嗯嗯嗯，楼主加油！

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AM335x启动流程（BootRom->MLO->Uboot）

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