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这里单独分析中断分发函数，大部分是基于汇编，初始化过程在另一个博客单独分析。
首先当中断来了之后硬件会自动跳转到函数：
(这里进行了部分删减，方便进行查看过程。)
.ent excNormVmVec.set noat
FUNC_LABEL(excNormVmVec).set noreorder
#ifdef _WRS_MIPS_VR4131_ERRATAnop /* 延时作用 */
#endif /* _WRS_MIPS_VR4131_ERRATA */mfc0 k0, C0_CAUSE /*取cause寄存器的值 */HAZARD_CP_READand k0, CAUSE_EXCMASK /*取cause code码 */bne k0, zero, 1f /*如果code码==0说明是中断 */nopla k0, excIntVmStubj k0 /*中断跳转到excIntVmStub函数，进行具体的分发 */nop
excNormVmVecEnd:.set at.set reorderFUNC_END(excNormVmVec).end excNormVmVec.sdata
.align 4
excNormVmVecSize:
.word excNormVmVecEnd-excNormVmVec
.text
这是excIntVmStub函数：
.globl excIntVmStub.ent excIntVmStub
FUNC_LABEL(excIntVmStub)
//保存相关的寄存器值SW AT, EXCPAGE_EXCSTUB_AT(zero)SW t7, EXCPAGE_EXCSTUB_T7(zero)SW t8, EXCPAGE_EXCSTUB_T8(zero)SW t9, EXCPAGE_EXCSTUB_T9(zero).set noreordermfc0 t7, C0_EPC /*读取epc的值*/mfc0 t8, C0_SR /*读取SR寄存器*/mfc0 t9, C0_CAUSE /*读取cause寄存器*/HAZARD_CP_READ.set reordersw t7, EXCPAGE_EXCSTUB_PC(zero) /*保存epc*/sw t8, EXCPAGE_EXCSTUB_SR(zero) /*保存SR*/sw t9, EXCPAGE_EXCSTUB_CR(zero) /*保存cause*//*关中断，并清楚exl*注意：在清中断前清楚exl，interrupts could be re-enabled here* for one or more cycles。所以在做完其他操作后，在去清楚exl位*/and t9, t8, ~(SR_KSUMASK|SR_IE) /*关中断，并清除用户权限位进入特权级 */.set noreordermtc0 t9, C0_SR HAZARD_INTERRUPT.set reorderand t9, ~SR_EXL /*清除exl */.set noreordermtc0 t9, C0_SRHAZARD_CP_WRITE.set reorder/*检查是否在中断栈中，增加areWeNested的值并保存*/_MIPS_PER_CPU_ARCH_VALUE_AND_ADRS_GET(t7,t8,areWeNested).set noreorderbnez t7, nestedVm /* if in isr don't reset sp */move t9, sp.set reorder/*如果没有在中断栈上，获取中断栈的值 */_MIPS_PER_CPU_VALUE_GET(t9,vxIntStackBase)
nestedVm:subu t9, ESTKSIZE /* make room for frame */SW sp, E_STK_SP(t9) /* save sp on int stack */move sp, t9 /* init new int stack ptr *//* save areWeNested */add t9, t7, 1sw t9, 0(t8)SW gp, E_STK_GP(sp)la gp, _gp#ifdef _WRS_CONFIG_SMP_MIPS_PER_CPU_VALUE_GET(t8,errno)
#else /* _WRS_CONFIG_SMP */lw t8, _WRS_MIPS_SDA_OFFSET(errno)
#endif /* _WRS_CONFIG_SMP */sw t8, E_ERRNO(sp)/*保存必要的值*/LW t9, EXCPAGE_EXCSTUB_AT(zero)SW t9, E_STK_AT(sp)LW t7, EXCPAGE_EXCSTUB_T7(zero)LW t8, EXCPAGE_EXCSTUB_T8(zero)LW t9, EXCPAGE_EXCSTUB_T9(zero)SW t7, E_STK_T7(sp)SW t8, E_STK_T8(sp)SW t9, E_STK_T9(sp)SW t0, E_STK_T0(sp) /* t0 saved here so a sputious int* won't lead it possibly getting* corrupted*/SW zero, E_STK_K0(sp) /* dummy value to k0 */SW zero, E_STK_K1(sp) /* dummy value to k1 */SW v0, E_STK_V0(sp) /* save func return 0, used *//* to hold cause */lw t9, EXCPAGE_EXCSTUB_PC(zero)lw t8, EXCPAGE_EXCSTUB_SR(zero)lw v0, EXCPAGE_EXCSTUB_CR(zero)sw t9, E_STK_EPC(sp) /* save EPC on stack */sw t8, E_STK_SR(sp) /* save status on stack */sw v0, E_STK_CAUSE(sp) /* save cause on stack */b commonExcIntStubCode /*跳转到正常中断处理函数中*/FUNC_END(excIntVmStub).end excIntVmStub
commonExcIntStubCode:SW ra, E_STK_RA(sp) /* save RA on stack */SW t0, E_STK_T0(sp) /* save temp reg 0 (early) */SW t1, E_STK_T1(sp) /* save temp reg 1 (early) */SW t2, E_STK_T2(sp) /* save temp reg 2 (early) */SW t3, E_STK_T3(sp) /* save temp reg 3 (early) */_MIPS_PER_CPU_VALUE_AND_ADRS_GET(t2,t1,intCnt)addu t2, 1 /* increment intCnt */sw t2, 0(t1)
excIntStubNormal:/* now t8 has STATUS and v0 has CAUSE */and t2, v0, SR_IMASK /* check for spurious interrupt */and v0, t8, t2 /* v0 = ints enabled and pending */.set noreorderbeqz v0, restoreVolatile /* return if no interrupt */move t1, zero /* flag only volatile restore* if branch is taken */
/* vxbus interrupt handler processing */sll t1, 4 /* mult by Prio table size */lw t2, intPrioTable+8(t1) /* get user mask */or v0, v0, t2 /* add user mask */not v0 /* invert interrupt mask */and t8, v0, t8 /* apply interrupt mask to t8 */
excIntStubCommonExit:and v0, t8, ~(SR_KSUMASK|SR_EXL|SR_IE).set noreordermtc0 v0, C0_SRHAZARD_INTERRUPT.set reorderand t8, ~(SR_KSUMASK|SR_EXL)mtc0 t8, C0_SR /* enable interrupts w/ new mask */HAZARD_CP_WRITE
/** Begin state save*/
intStateSave:SW zero,E_STK_ZERO(sp) /* init zero reg storage */SW v1,E_STK_V1(sp) /* save func return 1 */SW a0,E_STK_A0(sp) /* save passed param 0 */SW a1,E_STK_A1(sp) /* save passed param 1 */SW a2,E_STK_A2(sp) /* save passed param 2 */SW a3,E_STK_A3(sp) /* save passed param 3 */SW t0,E_STK_T0(sp) /* save temp reg 0 *//* save temp reg 1 (above) *//* save temp reg 2 (above) *//* save temp reg 3 (above) */SW t4,E_STK_T4(sp) /* save temp reg 4 */SW t5,E_STK_T5(sp) /* save temp reg 5 */SW t6,E_STK_T6(sp) /* save temp reg 6 *//* save temp reg 7 (above) *//* save temp reg 8 (above) *//* save temp reg 9 (above) *//* save return address (above) */mflo t2 /* read int mult lo reg */SW t2,E_STK_LO(sp) /* save int mult lo reg */mfhi t2 /* read int mult hi reg */SW t2,E_STK_HI(sp) /* save int mult hi reg *//* flag full context is being saved */sw zero, E_STK_ULEXTRA1(sp)MFC0 t2,C0_TLBHI /* read tlb entryHi reg */HAZARD_CP_READSW t2,E_STK_TLBHI(sp) /* save tlb entryHi reg */
/*进入C函数，进行中断的分发*/lw t2, _WRS_MIPS_SDA_OFFSET(_func_vxBusIntHdlr)beq t2, zero, 1fmove a0, t9 /* pass pin number of interrupt */.set noreorderjal t2 /* call registered vxBus ISR */move a1, sp /* pass exc stack frame */b Restore
在vxbMipsIntCtlrInstInit函数中对_func_vxBusIntHdlr进行了赋值操作：_func_vxBusIntHdlr = vxbMipsIntCtlrISR。也就是说真正的分发函数是：vxbMipsIntCtlrISR
void vxbMipsIntCtlrISR (int pinNum,ESFMIPS * pEsf){
#ifdef _WRS_CONFIG_SMPint cpunum = vxCpuIndexGet ();
#elseint cpunum = 0; /* UP and AMP always use zero cpu number */
#endif /* _WRS_CONFIG_SMP */struct vxbIntCtlrPin * pPin = vxbIntCtlrPinEntryGet(&(pVxbMipsIntCtlrDrvCtrl [cpunum]->isrHandle), pinNum);(*pPin->isr) ((void *)(pPin->pArg), (int)pEsf);}
在对中断进行初始化时，每个引脚对初始化为一个结构体，这个结构体包含了中断处理函数，所有最后分发时，只需要得到对应引脚的机构体，也就找到了具体的中断函数。
当然了每个中断函数的挂接，都是在中断初始化时所做的工作。后面对中断初始化分析时，会详细说明中断的挂接，以及相关结构体的初始化。
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