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这篇文章是lk启动流程分析(以高通为例),将会详细介绍下面的内容:
1).正常开机引导流程
2).recovery引导流程
3).fastboot引导流程
4).ffbm引导流程
5).lk向kernel传参
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在bootable/bootloader/lk/arch/arm/crt0.S文件中有下面代码,所以从kmain()开始介绍
bl kmain
kmain函数位于bootable/bootloader/lk/kernel/main.c
/* called from crt0.S */ void kmain(void) __NO_RETURN __EXTERNALLY_VISIBLE; void kmain(void) { // get us into some sort of thread context thread_init_early(); //初始化线程上下文 #ifdef FEATURE_AFTER_SALE_LOG_LK // do console early init console_init_early(); //初始化控制台 #endif // early arch stuff arch_early_init(); //架构初始化,如关闭cache,使能mmu // do any super early platform initialization platform_early_init(); //平台早期初始化 // do any super early target initialization target_early_init(); //目标设备早期初始化,初始化串口 dprintf(INFO, "welcome to lk "); bs_set_timestamp(BS_BL_START); // deal with any static constructors dprintf(SPEW, "calling constructors "); call_constructors(); // bring up the kernel heap dprintf(SPEW, "initializing heap "); heap_init(); //堆初始化 __stack_chk_guard_setup(); // initialize the threading system dprintf(SPEW, "initializing threads "); thread_init(); //线程初始化 #ifdef FEATURE_AFTER_SALE_LOG_LK // initialize the console layer dprintf(SPEW, "initializing console layer "); console_init(); //初始化控制台 #endif // initialize the dpc system dprintf(SPEW, "initializing dpc "); dpc_init(); //lk系统控制器初始化 // initialize kernel timers dprintf(SPEW, "initializing timers "); timer_init(); //kernel时钟初始化 #if (!ENABLE_NANDWRITE) // create a thread to complete system initialization dprintf(SPEW, "creating bootstrap completion thread "); thread_resume(thread_create("bootstrap2", &bootstrap2, NULL, DEFAULT_PRIORITY, DEFAULT_STACK_SIZE)); //创建一个线程初始化系统 // enable interrupts exit_critical_section(); //使能中断 // become the idle thread thread_become_idle(); //本线程切换成idle线程,idle为空闲线程,当没有更高优先级的线程时才执行 #else bootstrap_nandwrite(); #endif }
arch_early_init()负责使能内存管理单元mmu
bootable/bootloader/lk/arch/arm/arch.c void arch_early_init(void) { /* turn off the cache */ arch_disable_cache(UCACHE); //关闭cache /* set the vector base to our exception vectors so we dont need to double map at 0 */ #if ARM_CPU_CORTEX_A8 set_vector_base(MEMBASE); //设置异常向量基地址 #endif #if ARM_WITH_MMU arm_mmu_init(); //使能mmu #endif /* turn the cache back on */ arch_enable_cache(UCACHE); //打开cache #if ARM_WITH_NEON /* enable cp10 and cp11 */ uint32_t val; __asm__ volatile("mrc p15, 0, %0, c1, c0, 2" : "=r" (val)); val |= (3<<22)|(3<<20); __asm__ volatile("mcr p15, 0, %0, c1, c0, 2" :: "r" (val)); isb(); /* set enable bit in fpexc */ __asm__ volatile("mrc p10, 7, %0, c8, c0, 0" : "=r" (val)); val |= (1<<30); __asm__ volatile("mcr p10, 7, %0, c8, c0, 0" :: "r" (val)); #endif #if ARM_CPU_CORTEX_A8 /* enable the cycle count register */ uint32_t en; __asm__ volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (en)); en &= ~(1<<3); /* cycle count every cycle */ en |= 1; /* enable all performance counters */ __asm__ volatile("mcr p15, 0, %0, c9, c12, 0" :: "r" (en)); /* enable cycle counter */ en = (1<<31); __asm__ volatile("mcr p15, 0, %0, c9, c12, 1" :: "r" (en)); #endif }
platform_early_init()平台早期初始化,初始化平台的时钟和主板
bootableootloaderlkplatformmsm8952platform.c
void platform_early_init(void) { board_init(); //主板初始化 platform_clock_init(); //时钟初始化 qgic_init(); qtimer_init(); }
从代码可知,会创建一个bootstrap2线程,并使能中断
static int bootstrap2(void *arg) { dprintf(SPEW, "top of bootstrap2() "); arch_init(); //架构初始化,此函数为空,什么都没做 // XXX put this somewhere else #if WITH_LIB_BIO bio_init(); #endif #if WITH_LIB_FS fs_init(); #endif // initialize the rest of the platform dprintf(SPEW, "initializing platform "); platform_init(); // 平台初始化,不同的平台要做的事情不一样,可以是初始化系统时钟,超频等 // initialize the target dprintf(SPEW, "initializing target "); target_init(); //目标设备初始化,主要初始化Flash,整合分区表等 dprintf(SPEW, "calling apps_init() "); apps_init(); //应用功能初始化,主要调用boot_init,启动kernel,加载boot/recovery镜像等 return 0; }
apps_init()通过下面方式进入aboot_init()函数
APP_START(aboot)
.init = aboot_init,
APP_END
bootable/bootloader/lk/app/app.cvoid apps_init(void) { const struct app_descriptor *app; /* call all the init routines */ for (app = &__apps_start; app != &__apps_end; app++) { if (app->init) app->init(app); } /* start any that want to start on boot */ for (app = &__apps_start; app != &__apps_end; app++) { if (app->entry && (app->flags & APP_FLAG_DONT_START_ON_BOOT) == 0) { start_app(app); } } }
从这里开始是这篇文章的重点,分析aboot.c文件。每个项目的文件可能会有不同,但是差别会很小。
bootable/bootloader/lk/app/aboot/aboot.c void aboot_init(const struct app_descriptor *app) { unsigned reboot_mode = 0; unsigned restart_reason = 0; unsigned hard_reboot_mode = 0; bool boot_into_fastboot = false; uint8_t pon_reason = pm8950_get_pon_reason(); //pm8950_get_pon_reason() 获取开机原因 /* Setup page size information for nv storage */ if (target_is_emmc_boot()) //检测是emmc还是flash存储,并设置页大小,一般是2048 { page_size = mmc_page_size(); page_mask = page_size - 1; } else { page_size = flash_page_size(); page_mask = page_size - 1; } ASSERT((MEMBASE + MEMSIZE) > MEMBASE); //断言,如果内存基地址+内存大小小于内存基地址,则直接终止错误 read_device_info(&device); //从devinfo分区表read data到device结构体 read_allow_oem_unlock(&device); //devinfo分区里记录了unlock状态,从device中读取此信息 /* Display splash screen if enabled */ if (!check_alarm_boot()) { dprintf(SPEW, "Display Init: Start "); target_display_init(device.display_panel); //显示splash,Splash也就是应用程序启动之前先启动一个画面,上面简单的介绍应用程序的厂商,厂商的LOGO,名称和版本等信息,多为一张图片 dprintf(SPEW, "Display Init: Done "); } #ifdef FEATURE_LOW_POWER_DISP_LK if(is_low_voltage) { //如果电量低,则显示关机动画,并关闭设备 mdelay(2000); //target_uninit(); target_display_shutdown(); shutdown_device(); } #endif is_alarm_boot = check_alarm_boot(); //检测开机原因是否是由于关机闹钟导致 target_serialno((unsigned char *) sn_buf); dprintf(SPEW,"serial number: %s ",sn_buf); memset(display_panel_buf, '