Chinaunix首页 | 论坛 | 博客
  • 博客访问: 1426245
  • 博文数量: 487
  • 博客积分: 161
  • 博客等级: 入伍新兵
  • 技术积分: 5064
  • 用 户 组: 普通用户
  • 注册时间: 2011-07-01 07:37
个人简介

只有偏执狂才能生存

文章分类

全部博文(487)

文章存档

2016年(10)

2015年(111)

2014年(66)

2013年(272)

2012年(28)

分类: LINUX

2013-05-28 09:30:06

硬件中断发生(qemu模拟设备)
1.硬件产生中断的接口
void qemu_set_irq(qemu_irq irq, int level);

2.中断过程
void qemu_set_irq(qemu_irq irq, int level)
{
    if (!irq)
        return;

    irq->handler(irq->opaque, irq->n, level);
}
设置中断控制器hander,大致分为三种情况
1.cpu_irq的hander===> pic_irq_request
2.内核模拟中断控制器的hander===>kvm_i8259_set_irq
3.用户模拟中断控制器的hander===>i8259_set_irq

/* PC hardware initialisation */
static void pc_init1()
{
   cpu_irq = qemu_allocate_irqs(pic_irq_request, NULL, 1);
#ifdef KVM_CAP_IRQCHIP
    if (kvm_enabled() && kvm_irqchip_in_kernel()) {
        isa_irq_state = qemu_mallocz(sizeof(*isa_irq_state));
        isa_irq = i8259 = kvm_i8259_init(cpu_irq[0]);
    } else
#endif
    {
        i8259 = i8259_init(cpu_irq[0]);
        isa_irq_state = qemu_mallocz(sizeof(*isa_irq_state));
        isa_irq_state->i8259 = i8259;
        isa_irq = qemu_allocate_irqs(isa_irq_handler, isa_irq_state, 24);
    }
先研究用户空间中断控制器的中断发生过程
static void i8259_set_irq(void *opaque, int irq, int level)
{
    PicState2 *s = opaque;
    pic_set_irq1(&s->pics[irq >> 3], irq & 7, level);
    pic_update_irq(s);
}
中断触发方式分为电平触发和边沿触发,isa设备大多数采用边沿触发,pci设备采用电平触发。
假如采用边沿触发,如果leveld等于1,并且没有等待的中断请求(没有pending中断请求),设置中断请求寄存器为1,另外设置pending中断请求为1.
如果有pending中断请求,并不设置中断请求寄存器,可见允许中断丢失。
/* set irq level. If an edge is detected, then the IRR is set to 1 */
static inline void pic_set_irq1(PicState *s, int irq, int level)
{
    int mask;
    mask = 1 << irq;
    if (s->elcr & mask) {
        /* level triggered */
        if (level) {
            s->irr |= mask;
            s->last_irr |= mask;
        } else {
            s->irr &= ~mask;
            s->last_irr &= ~mask;
        }
    } else {
        /* edge triggered */
        if (level) {
            if ((s->last_irr & mask) == 0)
                s->irr |= mask;
            s->last_irr |= mask;
        } else {
            s->last_irr &= ~mask;
        }
    }
}
每次有中断请求,必须调用该函数。该函数调用造成中断嵌套。另外必须话必须注入中断。什么情况下是必须呢?具体可参照pic_get_irq()函数。
这个函数对产生中断优先级和正在处理中断优先级进行比较,如果大于话,注入请求中断。注入中断时机由qemu_irq_raise触发的,下面列出该函数。
/* raise irq to CPU if necessary. must be called every time the active
   irq may change */
void pic_update_irq(PicState2 *s)
{
    /* look at requested irq */
    irq = pic_get_irq(&s->pics[0]);
    if (irq >= 0) {
        qemu_irq_raise(s->parent_irq);
    }
}
不要认为,好像又循环到中断入口了,实际没有,关键在于参数s->parent_irq,该参数实际调用cpu_irq的hander===> pic_irq_request
static inline void qemu_irq_raise(qemu_irq irq)
{           
    qemu_set_irq(irq, 1);
}  
目前只研究用户态模拟中断控制器i8259(剔除KVM模拟和apic中断控制器), cpu_interrupt函数实际中断目前虚拟处理器运行,为硬件中断注入做好准备,目前就是中断注入时机。如何中断(暂停)虚拟处理器运行呢,通过该函数pthread_kill(env->kvm_cpu_state.thread, SIG_IPI)中断处理器运行;        
 static void pic_irq_request(void *opaque, int irq, int level)
{
    CPUState *env = first_cpu;
        if (level)
            cpu_interrupt(env, CPU_INTERRUPT_HARD);
        else
            cpu_reset_interrupt(env, CPU_INTERRUPT_HARD);
    }
}
 
中断注入
中断注入负责将虚拟中断控制器采集的中断请求注入到虚拟处理器。需要处理两个问题,什么时候注入,如何注入?
static int kvm_main_loop_cpu(CPUState *env)
{
    while (1) {
        int run_cpu = !is_cpu_stopped(env);
        if (run_cpu && !kvm_irqchip_in_kernel()) {
            process_irqchip_events(env);
            run_cpu = !env->halted;
        }
        if (run_cpu) {
            kvm_cpu_exec(env);
            kvm_main_loop_wait(env, 0);
        } else {
            kvm_main_loop_wait(env, 1000);
        }
    }
    pthread_mutex_unlock(&qemu_mutex);
    return 0;
}
如果中断控制器不是内核空间模拟(用户空间模拟),进行中断注入。
kvm_main_loop_cpu-->kvm_cpu_exec-->kvm_run
int kvm_run(CPUState *env)
{

#if !defined(__s390__)
    if (!kvm->irqchip_in_kernel)
        run->request_interrupt_window = kvm_arch_try_push_interrupts(env);
#endif
}
1.首先满足三个条件
1)内核kvm准备好了接受中断注入
2)有中断请求并且为硬件中断请求
3)虚拟处理器运行中断(开中断)
2.获取中断请求号
3.kvm注入中断请求
int kvm_arch_try_push_interrupts(void *opaque)
{
    CPUState *env = cpu_single_env;
    int r, irq;

    if (kvm_is_ready_for_interrupt_injection(env) && 
        (env->interrupt_request & CPU_INTERRUPT_HARD) &&
        (env->eflags & IF_MASK)) { 
            env->interrupt_request &= ~CPU_INTERRUPT_HARD;
            irq = cpu_get_pic_interrupt(env);
            if (irq >= 0) { 
                r = kvm_inject_irq(env, irq);
                if (r < 0)
                    printf("cpu %d fail inject %x\n", env->cpu_index, irq);
            }
    }
        
    return (env->interrupt_request & CPU_INTERRUPT_HARD) != 0;
}
//////////////////////////////////////////////////////////////////

内核空间中断采集
中断控制器由两种8259和apic,这两个设备在用户空间模拟过程,在上面已分析。接下来看一下在内核态模拟,我们暂且称之为内核空间中断采集。
static void kvm_i8259_set_irq(void *opaque, int irq, int level)
{
    int pic_ret;
    if (kvm_set_irq(irq, level, &pic_ret)) {
        if (pic_ret != 0)
            apic_set_irq_delivered();
        return;
    }
}
进入通过/dev/kvm接口,进入内核。
long kvm_arch_vm_ioctl(struct file *filp,
                       unsigned int ioctl, unsigned long arg)
{
      case KVM_IRQ_LINE_STATUS:
        case KVM_IRQ_LINE: {
                struct kvm_irq_level irq_event;

                r = -EFAULT;
                if (copy_from_user(&irq_event, argp, sizeof irq_event))
                        goto out;
                if (irqchip_in_kernel(kvm)) {
                        __s32 status;
                        status = kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID,
                                        irq_event.irq, irq_event.level);
                        if (ioctl == KVM_IRQ_LINE_STATUS) {
                                irq_event.status = status;
                                if (copy_to_user(argp, &irq_event,
                                                        sizeof irq_event))
                                        goto out;
                        }
                        r = 0;
                }
                break;
        }
}
硬件中断进入8259和apic中断控制器
int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level)
{                               
        struct kvm_kernel_irq_routing_entry *e, irq_set[KVM_NR_IRQCHIPS];
        int ret = -1, i = 0;                            
        struct kvm_irq_routing_table *irq_rt;
        struct hlist_node *n;
                        
        trace_kvm_set_irq(irq, level, irq_source_id);
  
        /* Not possible to detect if the guest uses the PIC or the 
         * IOAPIC.  So set the bit in both. The guest will ignore
         * writes to the unused one.
         */ 
        rcu_read_lock();
        irq_rt = rcu_dereference(kvm->irq_routing);
        if (irq < irq_rt->nr_rt_entries)
                hlist_for_each_entry(e, n, &irq_rt->map[irq], link)
                        irq_set[i++] = *e;
        rcu_read_unlock();

        while(i--) {
                int r;
                r = irq_set[i].set(&irq_set[i], kvm, irq_source_id, level);
                if (r < 0)
                        continue;
    
                ret = r + ((ret < 0) ? 0 : ret);
        } 
    
        return ret;

为了简单化,我们只分析8259中断控制器
static int kvm_set_pic_irq(struct kvm_kernel_irq_routing_entry *e,
                           struct kvm *kvm, int irq_source_id, int level)
{
#ifdef CONFIG_X86
        struct kvm_pic *pic = pic_irqchip(kvm);
        level = kvm_irq_line_state(&pic->irq_states[e->irqchip.pin],
                                   irq_source_id, level);
        return kvm_pic_set_irq(pic, e->irqchip.pin, level);
#else
        return -1;
#endif
}
这里8259中断控制器代码,如用户态过程类似,可参考上面分析
int kvm_pic_set_irq(void *opaque, int irq, int level)
{
        struct kvm_pic *s = opaque;
        int ret = -1;

        pic_lock(s);
        if (irq >= 0 && irq < PIC_NUM_PINS) {
                ret = pic_set_irq1(&s->pics[irq >> 3], irq & 7, level);
                pic_update_irq(s);
                trace_kvm_pic_set_irq(irq >> 3, irq & 7, s->pics[irq >> 3].elcr,
                                      s->pics[irq >> 3].imr, ret == 0);
        } 
        pic_unlock(s);
    
        return ret; 

如果收到中断响应
/*
 * callback when PIC0 irq status changed
 */
static void pic_irq_request(void *opaque, int level)
{
        struct kvm *kvm = opaque;
        struct kvm_vcpu *vcpu = kvm->bsp_vcpu;
        struct kvm_pic *s = pic_irqchip(kvm);
        int irq = pic_get_irq(&s->pics[0]);

        s->output = level;
        if (vcpu && level && (s->pics[0].isr_ack & (1 << irq))) {
                s->pics[0].isr_ack &= ~(1 << irq);
                s->wakeup_needed = true;
        }
}

中断注入
中断注入实际是向客户机CPU注入一个事件,这个事件包括异常和外部中断和NMI。异常我们一般看作为同步,中断被认为异步。
硬件具体实现就中断注入实际就是设置VMCS中字段VM-Entry interruption-infomation字段。中断注入实际在VM运行前完成的,具体代码如下:
static int vcpu_enter_guest(struct kvm_vcpu *vcpu) {
     inject_pending_event(vcpu);
}
vcpu_enter_guest函数运行虚拟机,运行虚拟机代码已省掉。中断注入实际在VM运行前,接下来看看具体如何注入。
static void inject_pending_event(struct kvm_vcpu *vcpu)
{
   if (vcpu->arch.nmi_injected) {
                kvm_x86_ops->set_nmi(vcpu);
                return;
        }

   if (vcpu->arch.interrupt.pending) {
                kvm_x86_ops->set_irq(vcpu);
                return;
        }
     /* try to inject new event if pending */
        if (vcpu->arch.nmi_pending) {
                if (kvm_x86_ops->nmi_allowed(vcpu)) {
                        vcpu->arch.nmi_pending = false;
                        vcpu->arch.nmi_injected = true;
                        kvm_x86_ops->set_nmi(vcpu);
                }
        } else if (kvm_cpu_has_interrupt(vcpu)) {
                if (kvm_x86_ops->interrupt_allowed(vcpu)) {
                        kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu),
                                            false);
                        kvm_x86_ops->set_irq(vcpu);
                }
        }

}
首先用户态实现中断控制器,不可屏蔽中断和其他中断注入过程。用户态中断采集在qemu代码中实现
判断是否有等待注入中断,存在话立即注入
接下来内核态模拟的中断控制器,中断注入过程,不可屏蔽中断和其他中断注入过程。
判断KVM内核态是否有不可屏蔽中断,有并且客户机cpu允许中断话,注入中断到客户机cpu中。
判断KVM内核态是否有中断,有中断并且客户机cpu允许中断话,获取优先级高中断进行排队,注入中断到客户机cpu中。
另外一个情况,如果有中断但是客户机不允许中断,只能等待下一下中断注入。如果下一次有更高级别中断发生,该中断还是不能注入而选择更高级别中断注入。

/*      
 * check if there is pending interrupt without
 * intack.
 */     
int kvm_cpu_has_interrupt(struct kvm_vcpu *v)
{       
        struct kvm_pic *s;

        if (!irqchip_in_kernel(v->kvm))
                return v->arch.interrupt.pending;

        if (kvm_apic_has_interrupt(v) == -1) {  /* LAPIC */
                if (kvm_apic_accept_pic_intr(v)) {
                        s = pic_irqchip(v->kvm);        /* PIC */
                        return s->output;
                } else
                        return 0;
        }
        return 1; 
}

int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
{               
        int vector = kvm_apic_has_interrupt(vcpu);
        struct kvm_lapic *apic = vcpu->arch.apic;
        
        if (vector == -1)
                return -1;
                        
        apic_set_vector(vector, apic->regs + APIC_ISR);
        apic_update_ppr(apic);
        apic_clear_irr(vector, apic);
        return vector;
}
找到中断向量,设置ISR,清除中断请求寄存器。



static void apic_update_ppr(struct kvm_lapic *apic)
{
        u32 tpr, isrv, ppr;
        int isr;

        tpr = apic_get_reg(apic, APIC_TASKPRI);
        isr = apic_find_highest_isr(apic);
        isrv = (isr != -1) ? isr : 0;

        if ((tpr & 0xf0) >= (isrv & 0xf0))
                ppr = tpr & 0xff;
        else
                ppr = isrv & 0xf0;

        apic_debug("vlapic %p, ppr 0x%x, isr 0x%x, isrv 0x%x",
                   apic, ppr, isr, isrv);

        apic_set_reg(apic, APIC_PROCPRI, ppr);
}
获取tpr寄存器内容,查询当前待处理请求向量,TPR 寄存器接收 0~15 共 16 个值,对应 16 个 CPU 规定的中断优先级级别,值越大优
先级越高。CPU 只处理比 TPR 中值优先级别更高的中断。将Pending 在 IRR 上的中断是否发送给 CPU

TPR,task priority register,任务优先级寄存器,它确定当前 CPU 可处理什么优先级别
范围内的中断。CPU 只处理比 TPR 中值优先级别更高的中断.
PPR,Processor priority register,处理器优先级寄存器。该寄存器决定当前 CPU 正在处
理的中断的优先级级别,以确定一个 Pending 在 IRR 上的中断是否发送给 CPU。与 TPR 不
同,它的值由 CPU 写而不是软件写。

static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu)
{
        return (vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF) &&
                !(vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) &
                        (GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS));
}
判断客户机中断标志寄存器和判断中断能力信息
static inline void kvm_queue_interrupt(struct kvm_vcpu *vcpu, u8 vector,
        bool soft)
{               
        vcpu->arch.interrupt.pending = true;
        vcpu->arch.interrupt.soft = soft;
        vcpu->arch.interrupt.nr = vector;
}

static void vmx_inject_irq(struct kvm_vcpu *vcpu)
{
        struct vcpu_vmx *vmx = to_vmx(vcpu);
        uint32_t intr;
        int irq = vcpu->arch.interrupt.nr;

        trace_kvm_inj_virq(irq);

        ++vcpu->stat.irq_injections;
    intr = irq | INTR_INFO_VALID_MASK;
        if (vcpu->arch.interrupt.soft) {
                intr |= INTR_TYPE_SOFT_INTR;
                vmcs_write32(VM_ENTRY_INSTRUCTION_LEN,
                             vmx->vcpu.arch.event_exit_inst_len);
        } else
                intr |= INTR_TYPE_EXT_INTR;
        vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr);
}
由结构体成员vcpu,获取包含该成员结构体vmx, 这个转换由container_of(ptr, type, member) 实现的,由兴趣可以自己分析一下。
接下来设置VM-Entry interruption-infomation字段,字段格式如下:
0-7为中断向量
8-10位为中断类型
11错误代码
12-30为保留
31为有效
设置中断信息字段的中断向量,并将中断信息字段最高位(31)为置1,1表明中断有效。
根据中断向量类型为软中断或者硬件中断,设置中断信息字段。
最后把写入中断信息字段到VMCS的数据域,从而完成中断注入。

int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level)
{
        u32 old_irr;
        u32 mask = 1 << irq;
        union kvm_ioapic_redirect_entry entry;
        int ret = 1;

        spin_lock(&ioapic->lock);
        old_irr = ioapic->irr;
        if (irq >= 0 && irq < IOAPIC_NUM_PINS) {
                entry = ioapic->redirtbl[irq];
                level ^= entry.fields.polarity;
                if (!level)
                        ioapic->irr &= ~mask;
                else {
                        int edge = (entry.fields.trig_mode == IOAPIC_EDGE_TRIG);
                        ioapic->irr |= mask;
                        if ((edge && old_irr != ioapic->irr) ||
                            (!edge && !entry.fields.remote_irr))
                                ret = ioapic_service(ioapic, irq);
                        else
                                ret = 0; /* report coalesced interrupt */
                }
                trace_kvm_ioapic_set_irq(entry.bits, irq, ret == 0);
        }
        spin_unlock(&ioapic->lock);

        return ret;
}
注意:中断请求寄存器表示已接受的中断,但是尚未提交
获取中断请求寄存器内容。
判断irq引脚线是否小于24
获取相应引脚重定向表内容,触发电平异或中断管脚的极性,主要因为entry.fields.polarity为0表示高电平有效,level为1将表示产生中断
获取触发模式,设置中断请求寄存器,如果为边沿触发并且没有排队中断,当中断是 level 触发时,LAPIC 接收了该中断,remote_irr内容为1,LAPIC 写 EOI 时,remote_irr内容为0


static int ioapic_service(struct kvm_ioapic *ioapic, unsigned int idx)
{       
        union kvm_ioapic_redirect_entry *pent; 
        int injected = -1;
                
        pent = &ioapic->redirtbl[idx];
                        
        if (!pent->fields.mask) {
                injected = ioapic_deliver(ioapic, idx);
                if (injected && pent->fields.trig_mode == IOAPIC_LEVEL_TRIG)
                        pent->fields.remote_irr = 1;
        }                   
                                
        return injected;
}  
如果中断屏蔽位没有设置,允许中断。

static int ioapic_deliver(struct kvm_ioapic *ioapic, int irq)
{
        union kvm_ioapic_redirect_entry *entry = &ioapic->redirtbl[irq];
        struct kvm_lapic_irq irqe;

        ioapic_debug("dest=%x dest_mode=%x delivery_mode=%x "
                     "vector=%x trig_mode=%x\n",
                     entry->fields.dest, entry->fields.dest_mode,
                     entry->fields.delivery_mode, entry->fields.vector,
                     entry->fields.trig_mode);

        irqe.dest_id = entry->fields.dest_id;
        irqe.vector = entry->fields.vector;
        irqe.dest_mode = entry->fields.dest_mode;
        irqe.trig_mode = entry->fields.trig_mode;
        irqe.delivery_mode = entry->fields.delivery_mode << 8;
        irqe.level = 1;
        irqe.shorthand = 0;

#ifdef CONFIG_X86
        /* Always delivery PIT interrupt to vcpu 0 */
        if (irq == 0) {
                irqe.dest_mode = 0; /* Physical mode. */
                /* need to read apic_id from apic regiest since
                 * it can be rewritten */
                irqe.dest_id = ioapic->kvm->bsp_vcpu->vcpu_id;
        }
#endif
        return kvm_irq_delivery_to_apic(ioapic->kvm, NULL, &irqe);
}
获取中断目的地,中断向量,中断目的模式,中断触发模式,中断触发方式,中断触发电平。如果中断中断,重新设置中断目的地。将中断发往目的地local apic
int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
                struct kvm_lapic_irq *irq)
{
        int i, r = -1;
        struct kvm_vcpu *vcpu, *lowest = NULL;

        if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
                        kvm_is_dm_lowest_prio(irq)) 
                printk(KERN_INFO "kvm: apic: phys broadcast and lowest prio\n");
    
        kvm_for_each_vcpu(i, vcpu, kvm) {
                if (!kvm_apic_present(vcpu))
                        continue;  
    
                if (!kvm_apic_match_dest(vcpu, src, irq->shorthand,
                                        irq->dest_id, irq->dest_mode))
                        continue;

                if (!kvm_is_dm_lowest_prio(irq)) {
                        if (r < 0)
                                r = 0;
                        r += kvm_apic_set_irq(vcpu, irq);
                } else if (kvm_lapic_enabled(vcpu)) {
                        if (!lowest)
                                lowest = vcpu;
                        else if (kvm_apic_compare_prio(vcpu, lowest) < 0)
                                lowest = vcpu;
                }
        }

        if (lowest)
                r = kvm_apic_set_irq(lowest, irq);
}
如果为Physical Mode,并且dest_id=0xff目的地为广播,是lowest priority,打印警告信息。
寻找匹配vpic,找到话,是Delivery mode 为 lowest priority,这样 IOAPIC 的中断消息由优先级最低的 CPU 接收。不是话,触发中断。

static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
                             int vector, int level, int trig_mode)
{
        int result = 0;
        struct kvm_vcpu *vcpu = apic->vcpu;

        switch (delivery_mode) {
        case APIC_DM_LOWEST:
                vcpu->arch.apic_arb_prio++;
        case APIC_DM_FIXED:
                /* FIXME add logic for vcpu on reset */
                if (unlikely(!apic_enabled(apic)))
                        break;

                if (trig_mode) {
                        apic_debug("level trig mode for vector %d", vector);
                        apic_set_vector(vector, apic->regs + APIC_TMR);
                } else
                        apic_clear_vector(vector, apic->regs + APIC_TMR);

                result = !apic_test_and_set_irr(vector, apic);
                trace_kvm_apic_accept_irq(vcpu->vcpu_id, delivery_mode,
                                          trig_mode, vector, !result);
                if (!result) {
                        if (trig_mode)
                                apic_debug("level trig mode repeatedly for "
                                                "vector %d", vector);
                        break;
                }

                kvm_vcpu_kick(vcpu);
                break;

设置TSR 即 Trigger Mode Register,用于表示当前正在处理中断的触发模式。1 为 level,0 为 edge,置中断请求寄存器。

kvm_vcpu_kick 产生处理器中断ipi ,重新调度,为中断注入做准备。

Destination Field,目的字段,R/W(可读写)。根据Destination Filed(见下)值的不同,该字段值的意义不同,它有两个意义:
Physical Mode(Destination Mode为0时): 其值为APIC ID,用于标识一个唯一的APIC。
Logical Mode(Destination Mode为1时):其值根据LAPIC的不同配置,代表一组CPU(具体见LAPIC相关内容)

Interrupt Vector,中断向量,R/W。指定该中断对应的vector,范围从10h到FEh(x86架构前16个vector被系统预留,见后面相关内容)
表1-1 RTE格式
当IOAPIC某个管脚接收到中断信号后,会根据该管脚对应的RTE,格式化出一条中断消息,发送给某个CPU的LAPIC。从上表我们可以看出,该消息包含了一个中断的所有信息。

Destination Mode,目的地模式,R/W。
0:Physical Mode,解释见Destination Field
1:Logical Mode,同上

Delivery Mode,传送模式,R/W。用于指定该中断以何种方式发送给目的APIC,各种模式需要和相应的触发方式配合。可选的模式如下,字段相应的值以二进制表示:
Fixed: 000b,发送给Destination Filed列出的所有CPU,level、edge触发均可。
Lowest Priority:001b,发送给Destination Filed列出的CPU中,优先级最低的CPU(CPU的优先级见LAPIC相关内容)。Level、edge均可
SMI:010b,System Management Interrupt,系统管理中断。只能为edge触发,并且vector字段写0
NMI:100b,None Mask Interrupt,不可屏蔽中断。发送给Destination Field列出的所有CPU,Vector字段值被忽略。NMI是edge触发,Trigger Mode字段中的值对NMI无影响,但建议配置成edge。
INIT:101b,发送给Destination Filed列出的所有CPU,LAPIC收到后执行INIT中断(详细信息参考相关CPU spec中INIT中断一节)。触发模式同NMI。
ExtINT:111b,发送给Destination Filed列出的所有CPU。CPU收到该中断后,认为这是一个PIC发送的中断请求,并回应INTA信号(该INTA脚连接到的是与该管脚相连的PIC上,而非IOAPIC上)
笔者:ExtINT用于PIC接在APIC上的情况,见后面的Virtual Wire Mode

15
Trigger Mode,触发模式,R/W。指明该管脚的的中断由什么方式触发。
1:Level,电平触发
2:Edge,边沿触发

阅读(10787) | 评论(0) | 转发(4) |
给主人留下些什么吧!~~