U-Boot-1.2.0源码学习（2）

书接上回，执行流进入到 lib_arm/board.c 中的 start_armboot 函数：

 

1.为 gd, bd 分配空间：

gd = (gd_t *)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));

 

gd_t 在 include/asm-arm/global_data.h 中有如下定义：

 

typedef struct global_data { .....} gd_t;

 

gd->bd = (bd_t *)((char *)gd - sizeof(bd_t));

 

bd_t 在 include/asm-arm/u-boot.h 中有下列定义：

 

typedef struct bd_info { ... } bd_t;

 

2. 执行初始化函数列表：

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

 其中 init_fnc_ptr 的类型为 init_fnc_t，其定义为 typedef int (init_fnc_t)(void);

init_sequence 是一个函数指针数组，成员有 cpu_init, board_init, interrupt_init, env_init, init_baudrate,serial_init .....

 

其中 cpu_init 在 cpu/arm920t 中的 cpu.c 中定义，由于没有定义 CONFIG_USE_IRQ 宏，故该函数直接返回：

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

board_init 函数定义在 board/smdk2410/smdk2410.c 中,完成板子时钟设置，IO口设置，打开数据与指令缓存的操作：

int board_init (void) { S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER(); S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO(); /* to reduce PLL lock time, adjust the LOCKTIME register */ clk_power->LOCKTIME = 0xFFFFFF; /* configure MPLL */ clk_power->MPLLCON = ((M_MDIV << 12) + (M_PDIV << 4) + M_SDIV); /* some delay between MPLL and UPLL */ delay (4000); /* configure UPLL */ clk_power->UPLLCON = ((U_M_MDIV << 12) + (U_M_PDIV << 4) + U_M_SDIV); /* some delay between MPLL and UPLL */ delay (8000); /* 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; /* arch number of SMDK2410-Board */ gd->bd->bi_arch_number = MACH_TYPE_SMDK2410; /* adress of boot parameters */ gd->bd->bi_boot_params = 0x30000100; icache_enable(); dcache_enable(); return 0; }

 interrupt_init 函数设置并启动定时器，其定义在 cpu/arm920t/s3c24x0 下的 interrupts.c 中：

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); }

env_init 函数有多个版本，在common目录下的 env_dataflash.c env_flash.c env_nand.c env_nowhere.c env_nvram.c env_eeprom.c 中均有定义，具体使用哪个则根据这些C文件开头的宏来决定，比如如果定义了 CFG_ENV_IS_IN_NAND 则使用 env_nand.c中的版本：

int env_init(void) { #if defined(ENV_IS_EMBEDDED) ulong total; int crc1_ok = 0, crc2_ok = 0; env_t *tmp_env1, *tmp_env2; total = CFG_ENV_SIZE; tmp_env1 = env_ptr; tmp_env2 = (env_t *)((ulong)env_ptr + CFG_ENV_SIZE); crc1_ok = (crc32(0, tmp_env1->data, ENV_SIZE) == tmp_env1->crc); crc2_ok = (crc32(0, tmp_env2->data, ENV_SIZE) == tmp_env2->crc); if (!crc1_ok && !crc2_ok) gd->env_valid = 0; else if(crc1_ok && !crc2_ok) gd->env_valid = 1; else if(!crc1_ok && crc2_ok) gd->env_valid = 2; else { /* both ok - check serial */ if(tmp_env1->flags == 255 && tmp_env2->flags == 0) gd->env_valid = 2; else if(tmp_env2->flags == 255 && tmp_env1->flags == 0) gd->env_valid = 1; else if(tmp_env1->flags > tmp_env2->flags) gd->env_valid = 1; else if(tmp_env2->flags > tmp_env1->flags) gd->env_valid = 2; else /* flags are equal - almost impossible */ gd->env_valid = 1; } if (gd->env_valid == 1) env_ptr = tmp_env1; else if (gd->env_valid == 2) env_ptr = tmp_env2; #else /* ENV_IS_EMBEDDED */ gd->env_addr = (ulong)&default_environment[0]; gd->env_valid = 1; #endif /* ENV_IS_EMBEDDED */ return (0); }