ARM移植之BootLoader(4)

4. BootLoader第二阶段

　　vivi Bootloader的第二阶段又分成了八个小阶段，在main函数中分别调用这几个小阶段的相关函数：

int main(int argc, char *argv[]) { int ret; /* * Step 1: */ putstr("\r\n"); putstr(vivi_banner); reset_handler(); /* * Step 2: */ ret = board_init(); if (ret) { putstr("Failed a board_init() procedure\r\n"); error(); } /* * Step 3: */ mem_map_init(); mmu_init(); putstr("Succeed memory mapping.\r\n"); /* * Now, vivi is running on the ram. MMU is enabled. */ /* * Step 4: */ /* initialize the heap area*/ ret = heap_init(); if (ret) { putstr("Failed initailizing heap region\r\n"); error(); } /* Step 5: */ ret = mtd_dev_init(); /* Step 6: */ init_priv_data(); /* Step 7: */ misc(); init_builtin_cmds(); /* Step 8: */ boot_or_vivi(); return 0; }

　　STEP1的putstr(vivi_banner)语句在串口输出一段字符说明vivi的版本、作者等信息，vivi_banner定义为：

const char *vivi_banner = "VIVI version " VIVI_RELEASE " (" VIVI_COMPILE_BY "@" VIVI_COMPILE_HOST ") (" VIVI_COMPILER ") " UTS_VERSION "\r\n";

　　reset_handler进行相应的复位处理：

void reset_handler(void) { 　int pressed; 　pressed = is_pressed_pw_btn(); 　if (pressed == PWBT_PRESS_LEVEL) { 　　DPRINTK("HARD RESET\r\n"); 　　hard_reset_handle(); 　} else { 　　DPRINTK("SOFT RESET\r\n"); 　　soft_reset_handle(); 　} }

　　hard_reset_handle会clear内存，而软件复位处理则什么都不做：

static void hard_reset_handle(void) { 　clear_mem((unsigned long)USER_RAM_BASE, (unsigned long)USER_RAM_SIZE); }

　　STEP2进行板初始化，设置时间和可编程I/O口：

int board_init(void) { 　init_time(); 　set_gpios(); 　return 0; }

　　STEP3进行内存映射及MMU初始化：

void mem_map_init(void) { 　#ifdef CONFIG_S3C2410_NAND_BOOT 　　mem_map_nand_boot(); 　#else 　　mem_map_nor(); 　#endif 　cache_clean_invalidate(); 　tlb_invalidate(); }

　　S3C2410A的MMU初始化只需要调用通用的arm920 MMU初始化函数：

static inline void arm920_setup(void) { unsigned long ttb = MMU_TABLE_BASE; __asm__( /* Invalidate caches */ "mov r0, #0\n" "mcr p15, 0, r0, c7, c7, 0\n" /* invalidate I,D caches on v4 */ "mcr p15, 0, r0, c7, c10, 4\n" /* drain write buffer on v4 */ "mcr p15, 0, r0, c8, c7, 0\n" /* invalidate I,D TLBs on v4 */ /* Load page table pointer */ "mov r4, %0\n" "mcr p15, 0, r4, c2, c0, 0\n" /* load page table pointer */ /* Write domain id (cp15_r3) */ "mvn r0, #0\n" /* Domains 0, 1 = client */ "mcr p15, 0, r0, c3, c0, 0\n" /* load domain access register */ /* Set control register v4 */ "mrc p15, 0, r0, c1, c0, 0\n" /* get control register v4 */ /* Clear out unwanted bits (then put them in if we need them) */ /* .RVI ..RS B... .CAM */ "bic r0, r0, #0x3000\n" /* ..11 .... .... .... */ "bic r0, r0, #0x0300\n" /* .... ..11 .... .... */ "bic r0, r0, #0x0087\n" /* .... .... 1... .111 */ /* Turn on what we want */ /* Fault checking enabled */ "orr r0, r0, #0x0002\n" /* .... .... .... ..1. */ #ifdef CONFIG_CPU_D_CACHE_ON "orr r0, r0, #0x0004\n" /* .... .... .... .1.. */ #endif #ifdef CONFIG_CPU_I_CACHE_ON "orr r0, r0, #0x1000\n" /* ...1 .... .... .... */ #endif /* MMU enabled */ "orr r0, r0, #0x0001\n" /* .... .... .... ...1 */ "mcr p15, 0, r0, c1, c0, 0\n" /* write control register */ : /* no outputs */ : "r" (ttb) ); }

　　STEP4设置堆栈；STEP5进行mtd设备的初始化，记录MTD分区信息；STEP6设置私有数据；STEP7初始化内建命令。

　　STEP8启动一个SHELL，等待用户输出命令并进行相应处理。在SHELL退出的情况下，启动操作系统：

#define DEFAULT_BOOT_DELAY 0x30000000 void boot_or_vivi(void) { char c; int ret; ulong boot_delay; boot_delay = get_param_value("boot_delay", &ret); if (ret) boot_delay = DEFAULT_BOOT_DELAY; /* If a value of boot_delay is zero, * unconditionally call vivi shell */ if (boot_delay == 0) vivi_shell(); /* * wait for a keystroke (or a button press if you want.) */ printk("Press Return to start the LINUX now, any other key for vivi\n"); c = awaitkey(boot_delay, NULL); if (((c != \r) && (c != \n) && (c != \0))) { printk("type \"help\" for help.\n"); vivi_shell(); } run_autoboot(); return; }