5.10.4 初始化定時器中斷
回到start_kernel,612行time_init函數:
void __init time_init(void) { late_time_init = x86_late_time_init; } |
函數x86_late_time_init實際上是初始化tsc時鐘源。在time_init中隻是把該函數的位址賦給全局變量late_time_init,以後某個時刻肯定會調用它的,這裡先提前詳細分析一下他:
static __init void x86_late_time_init(void) { x86_init.timers.timer_init(); tsc_init(); } |
x86_init.timers.timer_init實際是函數hpet_time_init,來自檔案kernel/timer.c:
101 void __init hpet_time_init(void) 102 { 103 if (!hpet_enable()) 104 setup_pit_timer(); 105 setup_default_timer_irq(); 106} |
由于我們沒有配置CONFIG_HPET_TIMER,是以103行hpet_enable傳回0,調用104行的函數setup_pit_timer,位于arch/x86/kernel/i8253.c:
104void __init setup_pit_timer(void) 105{ 106 110 pit_ce.cpumask = cpumask_of(smp_processor_id()); 111 pit_ce.mult = div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC, pit_ce.shift); 112 pit_ce.max_delta_ns = clockevent_delta2ns(0x7FFF, &pit_ce); 113 pit_ce.min_delta_ns = clockevent_delta2ns(0xF, &pit_ce); 114 115 clockevents_register_device(&pit_ce); 116 global_clock_event = &pit_ce; 117} |
整個函數的115行之前都是在通過彙編指令初始化全局變量pit_ce,這個clock_event_device類型的變量在編譯的時候已經被初始化成了:
static struct clock_event_device pit_ce = { .name = "pit", .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT, .set_mode = init_pit_timer, .set_next_event = pit_next_event, .shift = 32, .irq = 0, }; |
我們看到它的irq号為0,也就是對應32号中斷描述符表項,即interrupt[0]處理函數。115行把它注冊到通知鍊和clockevent_devices連結清單中:
void clockevents_register_device(struct clock_event_device *dev) { unsigned long flags; ……//一些調試代碼 raw_spin_lock_irqsave(&clockevents_lock, flags); list_add(&dev->list, &clockevent_devices); clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev); clockevents_notify_released(); raw_spin_unlock_irqrestore(&clockevents_lock, flags); } |
最後将全局global_clock_event設定成這個定時器,然後回到hpet_time_init中,105行,調用setup_default_timer_irq():
void __init setup_default_timer_irq(void) { setup_irq(0, &irq0); } static struct irqaction irq0 = { .handler = timer_interrupt, .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_IRQPOLL | IRQF_TIMER, .name = "timer" }; |
很簡單,調用setup_irq把interrupt[0]對應的處理函數設定成timer_interrupt。至于随後如何處理的,請檢視部落格“定時器中斷”
http://blog.csdn.net/yunsongice/archive/2010/03/07/5354137.aspx