l28n和开发版_*** am335x开发板的疑问以及解答
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:
< 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
}
#define CONFIG_SPL_TEXT_BASE0x402F0400
#define CONFIG_SPL_MAX_SIZE(46 * 1024)
#define CONFIG_SPL_STACKLOW_LEVEL_SRAM_STACK
#define CONFIG_SPL_BSS_START_ADDR0x80000000
#define CONFIG_SPL_BSS_MAX_SIZE0x80000/* 512 KB */
@1@ 保存启动参数bl save_boot_params
/*
* the actual reset code
*/
reset:
blsave_boot_params
.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
cmpr2, r0
bgt1f
ldrr2, =NON_SECURE_SRAM_END
cmpr2, r0
blt1f
/*
* store the boot params passed from rom code or saved
* and passed by SPL
*/
cmpr0, #0
beq1f
ldrr1, =boot_params
strr0, [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_START0x40304000
#define NON_SECURE_SRAM_END0x4030E000
#define LOW_LEVEL_SRAM_STACK0x4030B7FC
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
/*
* set the cpu to SVC32 mode
*/
mrsr0, cpsr
bicr0, r0, #0x1f
orrr0, r0, #0xd3
msrcpsr,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 status
register),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
@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
blcpu_init_crit
#endif
.globl lowlevel_init
lowlevel_init:
/*
* Setup a temporary stack
*/
ldrsp, =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
*/
bls_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
《PATH :/arch/arm/include/asm/arch-ti81xx/omap.h》
#define LOW_LEVEL_SRAM_STACK0x4030B7FC
@b2@ 执行 s_init() 函数,实现 CPU 的初始化
/*
* 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();
l2_cache_enable:
push{r0, r1, r2, lr}
mrc15, 0, r3, cr1, cr0, 1
orrr3, r3, #2
mcr15, 0, r3, cr1, cr0, 1
pop{r1, r2, r3, pc}
@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);
#define WDT_WSPR(WDT_BASE + 0x048)
/* Watchdog Timer */
#ifdef CONFIG_AM335X
#define WDT_BASE0x44E35000
#else
#define WDT_BASE0x480C2000
#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();
/*
* 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));
}
/* 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
/* 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_BASEUART0_BASE
#endif
#ifdef CONFIG_AM335X
#define UART0_BASE0x44E09000
#else
#define UART0_BASE0x48020000
#endif
@c6@ 初始化 定时器
/* 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_BASE0x4802C000
#define DM_TIMER1_BASE0x4802E000
#define DM_TIMER2_BASE0x48040000
#define DM_TIMER3_BASE0x48042000
#define DM_TIMER4_BASE0x48044000
#define DM_TIMER5_BASE0x48046000
#define DM_TIMER6_BASE0x48048000
#define DM_TIMER7_BASE0x4804A000
@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);
}
@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)
#defineDATA1_RANK0_DELAYS_0(DDR_PHY_BASE_ADDR + 0x1D8)
/* DDR offsets */
#defineDDR_PHY_BASE_ADDR0x44E12000
#defineDDR_IO_CTRL0x44E10E04
#defineDDR_CKE_CTRL0x44E1131C
#defineCONTROL_BASE_ADDR0x44E10000
@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:
ldrsp, =(CONFIG_SYS_INIT_SP_ADDR)
bicsp, sp, #7 /* 8-byte alignment for ABI compliance */
ldrr0,=0x00000000
blboard_init_f
#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_ADDRSRAM0_START
#define CONFIG_SYS_INIT_RAM_SIZESRAM0_SIZE
#ifdef CONFIG_AM335X
#define SRAM0_START0x402F0400
#else
#define SRAM0_START0x40300000
#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 */
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);
}
#define CONFIG_SPL_TEXT_BASE0x402F0400
#define CONFIG_SPL_MAX_SIZE(46 * 1024)
#define CONFIG_SPL_STACKLOW_LEVEL_SRAM_STACK
#define LOW_LEVEL_SRAM_STACK0x4030B7FC
/*
* void relocate_code (addr_sp, gd, addr_moni)
*
* This "function" does not return, instead it continues in RAM
* after relocating the monitor code.
*
*/
.globlrelocate_code
relocate_code:
movr4, r0/* save addr_sp */
movr5, r1/* save addr of gd */
movr6, 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:
movsp, r4
adrr0, _start
cmpr0, r6
moveqr9, #0/* no relocation. relocation offset(r9) = 0 */
beqclear_bss/* skip relocation */
movr1, r6/* r1
@a6@ 清空 bss 段
clear_bss:
ldrr0, _bss_start_ofs
ldrr1, _bss_end_ofs
movr4, r6/* reloc addr */
addr0, r0, r4
addr1, r1, r4
movr2, #0x00000000/* clear */
clbss_l:strr2, [r0]/* clear loop... */
addr0, r0, #4
cmpr0, r1
bneclbss_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
mcrp15, 0, r0, c7, c5, 0@ invalidate icache
mcr p15, 0, r0, c7, c10, 4@ DSB
mcr p15, 0, r0, c7, c5, 4@ ISB
#endif
ldrr0, _board_init_r_ofs
adrr1, _start
addlr, r0, r1
addlr, lr, r9
/* setup parameters for board_init_r */
movr0, r5/* gd_t */
movr1, r6/* dest_addr */
/* jump to it ... */
movpc, 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:
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。
/*
* 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)
*/
typedefstructglobal_data {
bd_t*bd;
unsigned longflags;
unsigned longbaudrate;
unsigned longhave_console;/* serial_init() was called */
unsigned longenv_addr;/* Address of Environment struct */
unsigned longenv_valid;/* Checksum of Environment valid? */
unsigned longfb_base;/* base address of frame buffer */
#ifdef CONFIG_FSL_ESDHC
unsigned longsdhc_clk;
#endif
#ifdef CONFIG_AT91FAMILY
/* "static data" needed by at91's clock.c */
unsigned longcpu_clk_rate_hz;
unsigned longmain_clk_rate_hz;
unsigned longmck_rate_hz;
unsigned longplla_rate_hz;
unsigned longpllb_rate_hz;
unsigned longat91_pllb_usb_init;
#endif
#ifdef CONFIG_ARM
/* "static data" needed by most of timer.c on ARM platforms */
unsigned longtimer_rate_hz;
unsigned longtbl;
unsigned longtbu;
unsigned long longtimer_reset_value;
unsigned longlastinc;
#endif
#ifdef CONFIG_IXP425
unsigned longtimestamp;
#endif
unsigned longrelocaddr;/* Start address of U-Boot in RAM */
phys_size_tram_size;/* RAM size */
unsigned longmon_len;/* monitor len */
unsigned longirq_sp;/* irq stack pointer */
unsigned longstart_addr_sp;/* start_addr_stackpointer */
unsigned longreloc_off;
#if !(defined(CONFIG_SYS_ICACHE_OFF) && defined(CONFIG_SYS_DCACHE_OFF))
unsigned longtlb_addr;
#endif
void**jt;/* jump table */
charenv_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 {
intbi_baudrate;/* serial console baudrate */
unsigned longbi_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:
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));
...
}
#define CONFIG_SYS_INIT_RAM_ADDRSRAM0_START
#define CONFIG_SYS_INIT_RAM_SIZESRAM0_SIZE
#define CONFIG_SYS_INIT_SP_ADDR(CONFIG_SYS_INIT_RAM_ADDR + \
CONFIG_SYS_INIT_RAM_SIZE - \
GENERATED_GBL_DATA_SIZE)
#define SRAM0_START0x402F0400
#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
/*
* Legacy format image header,
* all data in network byte order (aka natural aka bigendian).
*/
typedef struct image_header {
uint32_tih_magic;/* Image Header Magic Number*/
uint32_tih_hcrc;/* Image Header CRC Checksum*/
uint32_tih_time;/* Image Creation Timestamp*/
uint32_tih_size;/* Image Data Size*/
uint32_tih_load;/* Data Load Address*/
uint32_tih_ep;/* Entry Point Address*/
uint32_tih_dcrc;/* Image Data CRC Checksum*/
uint8_tih_os;/* Operating System*/
uint8_tih_arch;/* CPU architecture*/
uint8_tih_type;/* Image Type*/
uint8_tih_comp;/* Compression Type*/
uint8_tih_name[IH_NMLEN];/* Image Name*/
} image_header_t;
/*
* 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_BASE0x80800000
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