1.中断方式获取按键值单片机：
1)按键按下
2)cup发生中断,跳转到异常向量入口执行
3)b 函数a.保存被中断的现场b.执行中断处理函数c.恢复
linux:
1)trap_init()函数构造异常向量
2)vector_irq + stubs_offset 跳转,vector_irq用宏来实现a.保存寄存器的值b.asm_do_IRQc.恢复2.linux异常处理结构分析
---------------------------------------------
trap_init()函数构造了异常向量
把__vectors_start代码复制到vectors这个地址中去
---------------------------------------------1)/arch/arm/kernel/traps.ctrap_init(){memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start); ......}vectors    ====>   CONFIG_VECTORS_BASE 异常向量的地址，可配置项 2) /arch/arm/kernel/entry-armv.S__vectors_start分析:-------------------------------------------__vectors_start:        ARM(    swi    SYS_ERROR0    )THUMB(    svc    #0        )THUMB(    nop            )W(b)    vector_und + stubs_offset        @这些都是异常向量W(ldr)    pc, .LCvswi + stubs_offsetW(b)    vector_pabt + stubs_offsetW(b)    vector_dabt + stubs_offsetW(b)    vector_addrexcptn + stubs_offsetW(b)    vector_irq + stubs_offsetW(b)    vector_fiq + stubs_offset......
----------------------------------------------3)分析vector_undvector_und由vector_stub宏定义而来vector_stub und, UND_MODE
---------------------------------------------------------//宏定义.macro    vector_stub, name, mode, correction=0.align    5vector_\name:.if \correctionsub    lr, lr, #\correction.endif
　　......

//替换后    .macro    vector_stub, name, mode, correction=0.align    5vector_und:        @定义了一个标号@@ Save r0, lr_<exception> (parent PC) and spsr_<exception>@ (parent CPSR)@stmia    sp, {r0, lr}        @ save r0, lrmrs    lr, spsrstr    lr, [sp, #8]        @ save spsr@@ Prepare for SVC32 mode.  IRQs remain disabled.@mrs    r0, cpsreor    r0, r0, #(\mode ^ SVC_MODE | PSR_ISETSTATE)msr    spsr_cxsf, r0.......    .endm-------------------------------------------------------------
4).long    __und_usr            @  0 (USR_26 / USR_32) //作用：保存寄存器，做处理，恢复寄存器.long    __und_invalid            @  1 (FIQ_26 / FIQ_32).long    __und_invalid            @  2 (IRQ_26 / IRQ_32).long    __und_svc            @  3 (SVC_26 / SVC_32).long    __und_invalid            @  4.long    __und_invalid            @  5.long    __und_invalid            @  6.long    __und_invalid            @  7.long    __und_invalid            @  8.long    __und_invalid            @  9.long    __und_invalid            @  a.long    __und_invalid            @  b.long    __und_invalid            @  c.long    __und_invalid            @  d.long    __und_invalid            @  e.long    __und_invalid            @  f.align    5
-----------------------------------------------------------------
==========================================================================  分析vector_irq
1)W(b)    vector_irq + stubs_offset
-----------------------------------------------------------------
2)vector_stub    irq, IRQ_MODE, 4
替换后.macro    vector_stub, name, mode, correction=0.align    5vector_irq://计算返回地址
    sub    lr, lr, #\correction@@ Save r0, lr_<exception> (parent PC) and spsr_<exception>@ (parent CPSR)@stmia    sp, {r0, lr}        @ save r0, lrmrs    lr, spsrstr    lr, [sp, #8]        @ save spsr@@ Prepare for SVC32 mode.  IRQs remain disabled.@mrs    r0, cpsreor    r0, r0, #(\mode ^ SVC_MODE | PSR_ISETSTATE)msr    spsr_cxsf, r0@@ the branch table must immediately follow this code@and    lr, lr, #0x0fTHUMB(    adr    r0, 1f            )THUMB(    ldr    lr, [r0, lr, lsl #2]    )mov    r0, spARM(    ldr    lr, [pc, lr, lsl #2]    )movs    pc, lr            @ branch to handler in SVC mode
ENDPROC(vector_\name).align    2@ handler addresses follow this label
1:.endm
-----------------------------------------------------------
3).long    __irq_usr            @  0  (USR_26 / USR_32).long    __irq_invalid            @  1  (FIQ_26 / FIQ_32).long    __irq_invalid            @  2  (IRQ_26 / IRQ_32).long    __irq_svc            @  3  (SVC_26 / SVC_32).long    __irq_invalid            @  4.long    __irq_invalid            @  5.long    __irq_invalid            @  6.long    __irq_invalid            @  7.long    __irq_invalid            @  8.long    __irq_invalid            @  9.long    __irq_invalid            @  a.long    __irq_invalid            @  b.long    __irq_invalid            @  c.long    __irq_invalid            @  d.long    __irq_invalid            @  e.long    __irq_invalid            @  f------------------------------------------------------
4)__irq_usr分析：
__irq_usr: usr_entry                @入口kuser_cmpxchg_checkget_thread_info tsk
#ifdef CONFIG_PREEMPTldr    r8, [tsk, #TI_PREEMPT]        @ get preempt countadd    r7, r8, #1            @ increment itstr    r7, [tsk, #TI_PREEMPT]
#endifirq_handler                @处理函数
#ifdef CONFIG_PREEMPTldr    r0, [tsk, #TI_PREEMPT]str    r8, [tsk, #TI_PREEMPT]teq    r0, r7ARM(    strne    r0, [r0, -r0]    )THUMB(    movne    r0, #0        )THUMB(    strne    r0, [r0]    )
#endif
#ifdef CONFIG_TRACE_IRQFLAGSbl    trace_hardirqs_on
#endifmov    why, #0b    ret_to_userUNWIND(.fnend        )
ENDPROC(__irq_usr).ltorg.align    5
------------------------------------------------------
usr_entry分析：.macro    usr_entryUNWIND(.fnstart    )UNWIND(.cantunwind    )    @ don't unwind the user space
    sub    sp, sp, #S_FRAME_SIZE
 ARM(    stmib    sp, {r1 - r12}    )   @保存寄存器THUMB(    stmia    sp, {r0 - r12}    )ldmia    r0, {r1 - r3}add    r0, sp, #S_PC        @ here for interlock avoidancemov    r4, #-1            @  ""  ""     ""        ""str    r1, [sp]        @ save the "real" r0 copied@ from the exception stack.......endm
------------------------------------------------------------
irq_handler分析：.macro    irq_handlerget_irqnr_preamble r5, lr
1:    get_irqnr_and_base r0, r6, r5, lrmovne    r1, sp@@ routine called with r0 = irq number, r1 = struct pt_regs *@adrne    lr, BSYM(1b)bne    asm_do_IRQ            @跳转到C程序里面处理.......endm5) 调用asm_do_IRQ C处理程序