Zephyr启动过程与中断响应

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1. 启动过程

一般嵌入式处理器启动方式分为两种：
1. XIP 模式 (eXecute In Place)，在该模式下CPU直接从Nor Flash上读代码执行，执行速度慢；
2. 非XIP模式，在该模式下硬件先将代码从Flash上搬移到RAM上后，CPU才能从RAM上访问数据，执行速度快；

对于非XIP模式，启动前需要先借助boot把代码段从FLASH拷贝到RAM；

对于XIP模式，如果FLASH基地址映射到0地址，复位后可以直接启动；

如果FLASH基地址非0地址，启动之前需要先借助boot在映射的0地址（笔者项目的使用SOC通过bootlink将0地址映射到了0x20110000 ：IRAM_AON）中写入MSP的初始值+Reset入口地址（针对CortexM处理器）。

下文以CortexM + Zephyr1.9.2 +XIP模式为例进行相关阐述。

__reset

根据向量表找到的reset入口，位于(zephyr\arch\arm\core\cortex_m\reset.S)

reset入口完成工作：

初始化watchdog: _WdogInit
将中断栈_interrupt_stack内容初始化为0xaa
复位后CortexM处理器默认处于线程模式+特权访问+使用MSP主栈指针，这里切换为PSP指针并将PSP设为_interrupt_stack中断栈
进入C语言准备_PrepC

SECTION_SUBSEC_FUNC(TEXT,_reset_section,__reset)/** The entry point is located at the __reset symbol, which* is fetched by a XIP image playing the role of a bootloader, which jumps to* it, not through the reset vector mechanism. Such bootloaders might want to* search for a __start symbol instead, so create that alias here.*/
SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)/* lock interrupts: will get unlocked when switch to main task */cpsid i#ifdef CONFIG_WDOG_INIT/* board-specific watchdog initialization is necessary */bl _WdogInit
#endif#ifdef CONFIG_INIT_STACKSldr r0, =_interrupt_stackldr r1, =0xaaldr r2, =CONFIG_ISR_STACK_SIZEbl memset
#endif/** Set PSP and use it to boot without using MSP, so that it* gets set to _interrupt_stack during nanoInit().*/ldr r0, =_interrupt_stackldr r1, =CONFIG_ISR_STACK_SIZEadds r0, r0, r1msr PSP, r0movs.n r0, #2   /* switch to using PSP (bit1 of CONTROL reg) */msr CONTROL, r0b _PrepC

_PrepC

完成进入C语言环境后的准备工作，位于(zephyr\arch\arm\core\cortex_m\Prep_c.c)

_PrepC完成工作：

重定位向量表
使能浮点计算（如果有相关特性）
清零BSS段
从ROM拷贝数据段到RAM(针对XIP模式)
正式进入C环境执行

void _PrepC(void)
{relocate_vector_table();enable_floating_point();_bss_zero();_data_copy();
#ifdef CONFIG_BOOT_TIME_MEASUREMENT__start_time_stamp = 0;
#endif_Cstart();CODE_UNREACHABLE;
}

relocate_vector_table

根据CortexM处理器的特性，向量表固定于0地址，对于（XIP模式并且FLASH基地址非0）或者（非XIP模式并且RAM基地址非0）的情况，需要重新将向量表拷贝到0地址。

#define VECTOR_ADDRESS 0static inline void relocate_vector_table(void)
{
#if defined(CONFIG_XIP) && (CONFIG_FLASH_BASE_ADDRESS != 0) || \!defined(CONFIG_XIP) && (CONFIG_SRAM_BASE_ADDRESS != 0)size_t vector_size = (size_t)_vector_end - (size_t)_vector_start;memcpy(VECTOR_ADDRESS, _vector_start, vector_size);
#endif
}

_vector_end/_vector_start两个符号的地址在linker.ld链接脚本里面有定义，linker文件位于（zephyr\include\arch\arm\cortex_m\scripts）：

SECTION_PROLOGUE(_TEXT_SECTION_NAME,,){. = CONFIG_TEXT_SECTION_OFFSET;KEEP(*(.os.start))_vector_start = .;KEEP(*(.exc_vector_table))KEEP(*(".exc_vector_table.*"))KEEP(*(IRQ_VECTOR_TABLE))KEEP(*(.openocd_dbg))KEEP(*(".openocd_dbg.*"))/* Kinetis has to write 16 bytes at 0x400 */SKIP_TO_KINETIS_FLASH_CONFIGKEEP(*(.kinetis_flash_config))KEEP(*(".kinetis_flash_config.*"))#ifdef CONFIG_GEN_SW_ISR_TABLEKEEP(*(SW_ISR_TABLE))
#endif_vector_end = .;_image_text_start = .;*(.text)*(".text.*")*(.gnu.linkonce.t.*)} GROUP_LINK_IN(ROMABLE_REGION)_image_text_end = .;

_Cstart

正式进入C语言环境，开始操作系统初始化工作，位于(zephyr\kernel\init.c)

_Cstart完成工作：

多线程初始化
PRE_KERNEL_1、PRE_KERNEL_2级别设备初始化
切换到主线程开始运行

FUNC_NORETURN void _Cstart(void)
{
#ifdef CONFIG_TIME_TRACKinsert_pack_time_debug(PACK_AP_CSTART, NULL, -1);
#endif#ifdef CONFIG_ARCH_HAS_CUSTOM_SWAP_TO_MAINstruct k_thread *dummy_thread = NULL;
#elsestruct k_thread dummy_thread_memory;struct k_thread *dummy_thread = &dummy_thread_memory;
#endif/** Initialize kernel data structures. This step includes* initializing the interrupt subsystem, which must be performed* before the hardware initialization phase.*/prepare_multithreading(dummy_thread);/* perform basic hardware initialization */_sys_device_do_config_level(_SYS_INIT_LEVEL_PRE_KERNEL_1);_sys_device_do_config_level(_SYS_INIT_LEVEL_PRE_KERNEL_2);/* initialize stack canaries */
#ifdef CONFIG_STACK_CANARIES__stack_chk_guard = (void *)sys_rand32_get();
#endif/* display boot banner */switch_to_main_thread();/** Compiler can't tell that the above routines won't return and issues* a warning unless we explicitly tell it that control never gets this* far.*/CODE_UNREACHABLE;
}

prepare_multithreading

该函数完成多线程初始化，主要完成

中断（NVIC）初始化
创建了两个线程，分别是_main_thread（使用_main_stack，即系统入口对应的MSP指针）和_idle_thread（使用_idle_stack）
初始化_timeout_q超时队列
架构相关的内核初始化，针对CortexM主要完成MSP主栈设置为_interrupt_stack，以及中断异常相关初始化

static void prepare_multithreading(struct k_thread *dummy_thread)
{
#ifdef CONFIG_ARCH_HAS_CUSTOM_SWAP_TO_MAINARG_UNUSED(dummy_thread);
#else/** Initialize the current execution thread to permit a level of* debugging output if an exception should happen during kernel* initialization.  However, don't waste effort initializing the* fields of the dummy thread beyond those needed to identify it as a* dummy thread.*/_current = dummy_thread;dummy_thread->base.user_options = K_ESSENTIAL;dummy_thread->base.thread_state = _THREAD_DUMMY;
#endif/* _kernel.ready_q is all zeroes *//** The interrupt library needs to be initialized early since a series* of handlers are installed into the interrupt table to catch* spurious interrupts. This must be performed before other kernel* subsystems install bonafide handlers, or before hardware device* drivers are initialized.*/_IntLibInit();/* ready the init/main and idle threads */for (int ii = 0; ii < K_NUM_PRIORITIES; ii++) {sys_dlist_init(&_ready_q.q[ii]);}/** prime the cache with the main thread since:** - the cache can never be NULL* - the main thread will be the one to run first* - no other thread is initialized yet and thus their priority fields*   contain garbage, which would prevent the cache loading algorithm*   to work as intended*/_ready_q.cache = _main_thread;_new_thread(_main_thread, _main_stack,MAIN_STACK_SIZE, _main, NULL, NULL, NULL,CONFIG_MAIN_THREAD_PRIORITY, K_ESSENTIAL);_mark_thread_as_started(_main_thread);_add_thread_to_ready_q(_main_thread);#ifdef CONFIG_MULTITHREADING_new_thread(_idle_thread, _idle_stack,IDLE_STACK_SIZE, idle, NULL, NULL, NULL,K_LOWEST_THREAD_PRIO, K_ESSENTIAL);_mark_thread_as_started(_idle_thread);_add_thread_to_ready_q(_idle_thread);
#endifinitialize_timeouts();/* perform any architecture-specific initialization */kernel_arch_init();
}

_sys_device_do_config_level

设备初始化，Zephyr定义了四个级别的初始化，分别为：

#define _SYS_INIT_LEVEL_PRE_KERNEL_1 0
#define _SYS_INIT_LEVEL_PRE_KERNEL_2 1
#define _SYS_INIT_LEVEL_POST_KERNEL 2
#define _SYS_INIT_LEVEL_APPLICATION 3

_sys_device_do_config_level函数实现：

void _sys_device_do_config_level(int level)
{struct device *info;for (info = config_levels[level]; info < config_levels[level+1];info++) {struct device_config *device = info->config;device->init(info);
#ifdef CONFIG_TIME_TRACKinsert_pack_time_debug(ap_init_counter, device->init, level);ap_init_counter++;
#endif}
}

设备初始化接口定义：

SYS_INIT(netdog_work_q_init, APPLICATION, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT);#define SYS_INIT(init_fn, level, prio) \DEVICE_INIT(_SYS_NAME(init_fn), "", init_fn, NULL, NULL, level, prio)#define DEVICE_INIT(dev_name, drv_name, init_fn, data, cfg_info, level, prio) \DEVICE_AND_API_INIT(dev_name, drv_name, init_fn, data, cfg_info, \level, prio, NULL)#define DEVICE_AND_API_INIT(dev_name, drv_name, init_fn, data, cfg_info, \level, prio, api) \DEVICE_DEFINE(dev_name, drv_name, init_fn, \device_pm_control_nop, data, cfg_info, level, \prio, api)#define DEVICE_DEFINE(dev_name, drv_name, init_fn, pm_control_fn, \data, cfg_info, level, prio, api) \\static struct device_config _CONCAT(__config_, dev_name) __used \__attribute__((__section__(".devconfig.init"))) = { \.name = drv_name, .init = (init_fn), \.device_pm_control = (pm_control_fn), \.config_info = (cfg_info) \}; \static struct device _CONCAT(__device_, dev_name) __used \__attribute__((__section__(".init_" #level STRINGIFY(prio)))) = { \.config = &_CONCAT(__config_, dev_name), \.driver_api = api, \.driver_data = data \}

switch_to_main_thread

切换到_main_thread开始运行：

static void switch_to_main_thread(void)
{
#ifdef CONFIG_ARCH_HAS_CUSTOM_SWAP_TO_MAIN_arch_switch_to_main_thread(_main_thread, _main_stack, MAIN_STACK_SIZE,_main);
#else/** Context switch to main task (entry function is _main()): the* current fake thread is not on a wait queue or ready queue, so it* will never be rescheduled in.*/_Swap(irq_lock());
#endif
}

_main_thread线程入口为_main，_main函数完成：

平台相关的初始化以及_SYS_INIT_LEVEL_POST_KERNEL、SYS_INIT_LEVEL_APPLICATION级别设备初始化，这些初始化会创建相关的平台与应用线程；
完成后进入main钩子函数(\os\zephyr\samples\xxx\src\main.c)，本平台该函数实现为空；
该线程没有死循环入口，所以完成后自行退出，然后操作系统开始正式调度执行；

static void _main(void *unused1, void *unused2, void *unused3)
{ARG_UNUSED(unused1);ARG_UNUSED(unused2);ARG_UNUSED(unused3);oss_event_init();oss_icp_init();oss_nv_init();_reset_uart_termios();ramdump_init();amt_init();zcat_ap_init();_sys_device_do_config_level(_SYS_INIT_LEVEL_POST_KERNEL);/* Final init level before app starts */_sys_device_do_config_level(_SYS_INIT_LEVEL_APPLICATION);#if defined(CONFIG_BOOT_DELAY) && CONFIG_BOOT_DELAY > 0if (boot_delay > 0) {printk("delaying boot\n");k_sleep(CONFIG_BOOT_DELAY);}PRINT_BOOT_BANNER();
#endif_init_static_threads();#ifdef CONFIG_BOOT_TIME_MEASUREMENT/* record timestamp for kernel's _main() function */extern u64_t __main_time_stamp;__main_time_stamp = (u64_t)k_cycle_get_32();
#endifextern void main(void);k_thread_priority_set(_main_thread, CONFIG_MAIN_THREAD_PRIORITY);main();/* Terminate thread normally since it has no more work to do */_main_thread->base.user_options &= ~K_ESSENTIAL;
}

2. 中断响应

以CortexM0处理器为例，其异常列表如下：

异常类型　　　　　　异常编号　　　　　　  描述Reset　　　　　　　　  1　　　　　　　　　上电复位或系统复位NMI　　　　　　　　　  2　　　　　　　　　不可屏蔽中断Hard fault　　　　　　3　　　　　　　　　用于错误处理，系统检测到错误后被激活SVCall　　　　　　　  11　　　　　　　　 请求管理调用，在执行SVC指令被激活，主要用作操作系统PendSV　　　　　　　  14　　　　　　　　 可挂起服务（系统）调用SysTick　　　　　　　 15　　　　　　　　 系统节拍定时器异常，一般在OS种用作周期系统节拍异常IRQ0-IRQ31　　　　   16-47　　　　　　  中断，可来自于外部，也可来自片上外设

查看linker.ld文件可以看到，Zephyr系统将上述异常对应的向量表分成了几部分，分别为exc_vector_table，IRQ_VECTOR_TABLE和SW_ISR_TABLE；（忽略openocd_dbg、kinetis_flash_config段，未使用）：

        _vector_start = .;KEEP(*(.exc_vector_table))KEEP(*(".exc_vector_table.*"))KEEP(*(IRQ_VECTOR_TABLE))KEEP(*(.openocd_dbg))KEEP(*(".openocd_dbg.*"))/* Kinetis has to write 16 bytes at 0x400 */SKIP_TO_KINETIS_FLASH_CONFIGKEEP(*(.kinetis_flash_config))KEEP(*(".kinetis_flash_config.*"))#ifdef CONFIG_GEN_SW_ISR_TABLEKEEP(*(SW_ISR_TABLE))
#endif_vector_end = .;

第一部分，异常向量表exc_vector_table，位于（zephyr\arch\arm\core\cortex_m\vector_table.S），定义了1-15号异常对应的跳转PC地址:

 SECTION_SUBSEC_FUNC(exc_vector_table,_vector_table_section,_vector_table).word _main_stack + CONFIG_MAIN_STACK_SIZE.word __reset.word __nmi.word __hard_fault.word __reserved.word __reserved.word __reserved.word __reserved.word __reserved.word __reserved.word __reserved.word __svc.word __reserved.word __reserved.word __pendsv#if defined(CONFIG_CORTEX_M_SYSTICK).word _timer_int_handler#else.word __reserved#endif

第二部分，中断向量表IRQ_VECTOR_TABLE，定义了16-47号中断跳转PC地址，位于project\prj_XXX\temp\Isr_tables.c，这是一个正式编译前由gen_isr_tables.py Python脚本生成的文件；该向量表所有项都对应同一个函数即所有中断总入口，函数名为_isr_wrapper：

#define __irq_vector_table _GENERIC_SECTION(IRQ_VECTOR_TABLE)u32_t __irq_vector_table _irq_vector_table[34] = {0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,0xffc88cd,
};

第三部分，具体中断实现结构体SW_ISR_TABLE，同样位于project\prj_XXX\temp\Isr_tables.c，也是由Python脚本生成，该结构体由两项成员，分别为传入参数arg和中断入口isr：

#define __sw_isr_table  _GENERIC_SECTION(SW_ISR_TABLE)struct _isr_table_entry {  void *arg;  void (*isr)(void *); };struct _isr_table_entry __sw_isr_table _sw_isr_table[34] = {{(void *)0x10724, (void *)0xffb8479},{(void *)0x10670, (void *)0xffb4b59},{(void *)0x0, (void *)0xffc8759},{(void *)0x1067c, (void *)0xffb4b59},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffb9661},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},{(void *)0x10730, (void *)0xffb8aa9},{(void *)0x10730, (void *)0xffb8a5d},{(void *)0x106c4, (void *)0xffb52c9},{(void *)0x2, (void *)0xffc6ad1},{(void *)0x0, (void *)0xffc6ad1},{(void *)0x1061c, (void *)0xffb66f5},{(void *)0x10610, (void *)0xffb66f5},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc69e9},{(void *)0x0, (void *)0xffc8759},{(void *)0x10694, (void *)0xffb9b8b},{(void *)0x0, (void *)0xffc72e1},{(void *)0x106e8, (void *)0xffb6af3},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},{(void *)0x10730, (void *)0xffb8959},{(void *)0x0, (void *)0xffc8759},{(void *)0x106b8, (void *)0xffb52c9},{(void *)0x0, (void *)0xffc5e9d},{(void *)0x0, (void *)0xffc8759},{(void *)0x0, (void *)0xffc8759},
};

具体程序如何从_isr_wrapper总入口找到对应中断并进入对应中断入口，可以参考_isr_wrapper函数实现：

SECTION_FUNC(TEXT, _isr_wrapper)push {lr}     /* lr is now the first item on the stack *//** All interrupts are disabled when handling idle wakeup.  For tickless* idle, this ensures that the calculation and programming of the device* for the next timer deadline is not interrupted.  For non-tickless idle,* this ensures that the clearing of the kernel idle state is not* interrupted.  In each case, _sys_power_save_idle_exit is called with* interrupts disabled.*/cpsid i  /* PRIMASK = 1 *//* is this a wakeup from idle ? */ldr r2, =_kernel/* requested idle duration, in ticks */ldr r0, [r2, #_kernel_offset_to_idle]cmp r0, #0beq _idle_state_clearedmovs.n r1, #0/* clear kernel idle state */str r1, [r2, #_kernel_offset_to_idle]blx _sys_power_save_idle_exit
_idle_state_cleared:cpsie i     /* re-enable interrupts (PRIMASK = 0) */mrs r0, IPSR   /* get exception number */ldr r1, =16subs r0, r1   /* get IRQ number */lsls r0, #3 /* table is 8-byte wide */ldr r1, =_sw_isr_tableadd r1, r1, r0 /* table entry: ISRs must have their MSB set to stay* in thumb mode */ldm r1!,{r0,r3}   /* arg in r0, ISR in r3 */blx r3        /* call ISR */pop {r3}mov lr, r3/* exception return is done in _IntExit() */b _IntExit

中断定义与处理

中断定义接口如下：

 IRQ_CONNECT(SI_TIM0_IRQ, CONFIG_TIMER_0_IRQ_PRI,timer_si_isr, DEVICE_GET(timer_si_0), 0);

中断号：SI_TIM0_IRQ

中断处理函数：timer_si_isr

定义完成后通过脚本解析，timer_si_isr的地址会被写入sw_isr_table；下面的中断处理路径，通过timer中断实现了系统tick的处理：

timer_si_isr
timer_systick_callback
_sys_clock_final_tick_announce
_sys_clock_tick_announce
_nano_sys_clock_tick_announce
handle_timeouts
_handle_expired_timeouts
_handle_one_expired_timeout
work_timeout

转载于:https://www.cnblogs.com/DF11G/p/9774437.html

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