uboot启动第二阶段1

uboot启动第二阶段。在这个阶段中，uboot完成一些复杂的初始化，最终读取内核文件并启动内核。

主要流程：1、为gd   gb全局变量分配空间，并初始化

2、初始化列表

3、

4、

一、gd   bd全局变量分配空间、初始化

/* Pointer is writable since we allocated a register for it */gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));/* compiler optimization barrier needed for GCC >= 3.4 */__asm__ __volatile__("": : :"memory");memset ((void*)gd, 0, sizeof (gd_t));gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));memset (gd->bd, 0, sizeof (bd_t));monitor_flash_len = _bss_start - _armboot_start;

在内存的映射空间中保留了128B的字节给全局变量，gd     bd为全局变量数据，存放一些重要的数据。具体可以查找相关结构体。对分配的空间进行初始化，赋值0.

__asm__ __volatile__("": : :"memory");这一条指令告诉编译器，寄存器当前数值发生变化，存放的值无效。

monitor_flash_len存放代码大小

二、初始化列表

其中typedef int (init_fnc_t) (void);表示init_fnc_t 表示返回值为空、参数为空的函数指针。初始化列表对这种类型的函数进行初始化。

init_fnc_t **init_fnc_ptr;for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {if ((*init_fnc_ptr)() != 0) {hang ();}}

typedef int (init_fnc_t) (void);

init_fnc_t *init_sequence[] = {cpu_init,/* basic cpu dependent setup */board_init,/* basic board dependent setup */interrupt_init,/* set up exceptions */env_init,/* initialize environment */init_baudrate,/* initialze baudrate settings */serial_init,/* serial communications setup */console_init_f,/* stage 1 init of console */display_banner,/* say that we are here */#if defined(CONFIG_DISPLAY_CPUINFO)print_cpuinfo,/* display cpu info (and speed) */#endif#if defined(CONFIG_DISPLAY_BOARDINFO)checkboard,/* display board info */#endifdram_init,/* configure available RAM banks */display_dram_config,NULL,};

1、int cpu_init (void)

在uboot的第一阶段已经对cpu进行初始化，这里只是一个空函数

int cpu_init (void){/* * setup up stacks if necessary */#ifdef CONFIG_USE_IRQIRQ_STACK_START = _armboot_start - CFG_MALLOC_LEN - CFG_GBL_DATA_SIZE - 4;FIQ_STACK_START = IRQ_STACK_START - CONFIG_STACKSIZE_IRQ;#endifreturn 0;}

2、int board_init (void)

board初始化，主要完成GPIO初始化、时钟初始化、并对全局变量中gd中的启动参数与机器类型初始化、开启数据与代码cache。

int board_init (void){    S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER();    S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO();    /* set up the I/O ports */    gpio->GPACON = 0x007FFFFF;    gpio->GPBCON = 0x00044555;    gpio->GPBUP = 0x000007FF;    gpio->GPCCON = 0xAAAAAAAA;    gpio->GPCUP = 0x0000FFFF;    gpio->GPDCON = 0xAAAAAAAA;    gpio->GPDUP = 0x0000FFFF;    gpio->GPECON = 0xAAAAAAAA;    gpio->GPEUP = 0x0000FFFF;    gpio->GPFCON = 0x000055AA;    gpio->GPFUP = 0x000000FF;    gpio->GPGCON = 0xFF95FFBA;    gpio->GPGUP = 0x0000FFFF;    gpio->GPHCON = 0x002AFAAA;    gpio->GPHUP = 0x000007FF;    /* support both of S3C2410 and S3C2440, by www.100ask.net */    if ((gpio->GSTATUS1 == 0x32410000) || (gpio->GSTATUS1 == 0x32410002))    {        /* FCLK:HCLK:PCLK = 1:2:4 */        clk_power->CLKDIVN = S3C2410_CLKDIV;        /* change to asynchronous bus mod */        __asm__(    "mrc    p15, 0, r1, c1, c0, 0\n"    /* read ctrl register   */                      "orr    r1, r1, #0xc0000000\n"      /* Asynchronous         */                      "mcr    p15, 0, r1, c1, c0, 0\n"    /* write ctrl register  */                      :::"r1"                    );                /* to reduce PLL lock time, adjust the LOCKTIME register */        clk_power->LOCKTIME = 0xFFFFFF;        /* configure MPLL */        clk_power->MPLLCON = S3C2410_MPLL_200MHZ;        /* some delay between MPLL and UPLL */        delay (4000);        /* configure UPLL */        clk_power->UPLLCON = S3C2410_UPLL_48MHZ;        /* some delay between MPLL and UPLL */        delay (8000);                /* arch number of SMDK2410-Board */        gd->bd->bi_arch_number = MACH_TYPE_SMDK2410;    }    else    {        /* FCLK:HCLK:PCLK = 1:4:8 */        clk_power->CLKDIVN = S3C2440_CLKDIV;        /* change to asynchronous bus mod */        __asm__(    "mrc    p15, 0, r1, c1, c0, 0\n"    /* read ctrl register   */                      "orr    r1, r1, #0xc0000000\n"      /* Asynchronous         */                      "mcr    p15, 0, r1, c1, c0, 0\n"    /* write ctrl register  */                      :::"r1"                    );        /* to reduce PLL lock time, adjust the LOCKTIME register */        clk_power->LOCKTIME = 0xFFFFFF;        /* configure MPLL */        clk_power->MPLLCON = S3C2440_MPLL_400MHZ;        /* some delay between MPLL and UPLL */        delay (4000);        /* configure UPLL */        clk_power->UPLLCON = S3C2440_UPLL_48MHZ;        /* some delay between MPLL and UPLL */        delay (8000);                /* arch number of SMDK2440-Board */        gd->bd->bi_arch_number = MACH_TYPE_S3C2440;    }    /* adress of boot parameters */    gd->bd->bi_boot_params = 0x30000100;    icache_enable();    dcache_enable();    return 0;}

3、中断初始化，其实没有采用中断。让定时器采用10ms循环计数的方法，对时间进行标记。代码如下，实现过程可以参考datasheet。

int interrupt_init (void){S3C24X0_TIMERS * const timers = S3C24X0_GetBase_TIMERS();/* use PWM Timer 4 because it has no output *//* prescaler for Timer 4 is 16 */timers->TCFG0 = 0x0f00;if (timer_load_val == 0){/* * for 10 ms clock period @ PCLK with 4 bit divider = 1/2 * (default) and prescaler = 16. Should be 10390 * @33.25MHz and 15625 @ 50 MHz */timer_load_val = get_PCLK()/(2 * 16 * 100);}/* load value for 10 ms timeout */lastdec = timers->TCNTB4 = timer_load_val;/* auto load, manual update of Timer 4 */timers->TCON = (timers->TCON & ~0x0700000) | 0x600000;/* auto load, start Timer 4 */timers->TCON = (timers->TCON & ~0x0700000) | 0x500000;timestamp = 0;return (0);}

4、环境变量初始化

在环境变量的文章中有介绍，让gd的环境地址指向有效的环境地址。

int  env_init(void){#ifdef CONFIG_OMAP2420H4int flash_probe(void);if(flash_probe() == 0)goto bad_flash;#endifif (crc32(0, env_ptr->data, ENV_SIZE) == env_ptr->crc) {gd->env_addr  = (ulong)&(env_ptr->data);gd->env_valid = 1;return(0);}#ifdef CONFIG_OMAP2420H4bad_flash:#endifgd->env_addr  = (ulong)&default_environment[0];gd->env_valid = 0;return (0);}#ifdef CMD_SAVEENV

5、波特率初始化，就是查找波特率的值

如果环境变量中的参数没有波特率参数，采用程序的默认值

static int init_baudrate (void){char tmp[64];/* long enough for environment variables */int i = getenv_r ("baudrate", tmp, sizeof (tmp));gd->bd->bi_baudrate = gd->baudrate = (i > 0)? (int) simple_strtoul (tmp, NULL, 10): CONFIG_BAUDRATE;return (0);}

6串口初始化，串口初始化调用系统的时钟与波特率完成串口的初始化。

在完成串口初始化后，可以调用putc  puts getc等相关函数进行输入输出

int serial_init (void){serial_setbrg ();return (0);}

void serial_setbrg (void){S3C24X0_UART * const uart = S3C24X0_GetBase_UART(UART_NR);int i;unsigned int reg = 0;/* value is calculated so : (int)(PCLK/16./baudrate) -1 */reg = get_PCLK() / (16 * gd->baudrate) - 1;/* FIFO enable, Tx/Rx FIFO clear */uart->UFCON = 0x07;uart->UMCON = 0x0;/* Normal,No parity,1 stop,8 bit */uart->ULCON = 0x3;/* * tx=level,rx=edge,disable timeout int.,enable rx error int., * normal,interrupt or polling */uart->UCON = 0x245;uart->UBRDIV = reg;#ifdef CONFIG_HWFLOWuart->UMCON = 0x1; /* RTS up */#endiffor (i = 0; i < 100; i++);}

7控制台初始化（第一阶段），设置控制台的标志位

int console_init_f (void){gd->have_console = 1;#ifdef CONFIG_SILENT_CONSOLEif (getenv("silent") != NULL)gd->flags |= GD_FLG_SILENT;#endifreturn (0);}

8、 display_banner函数显示uboot的版本信息，在make文件中自动调用编译时间，好方便不用设置

9、 dram_init,display_dram_config。dram初始化，其实已经在uboot的第一阶段进行初始化了。在这里对bd变量中内存存储容量与存储地址进行初始化。显示出来。