字符设备驱动笔记——中断方式按键驱动之linux异常处理结构（四）

.中断方式获取按键值

单片机：
)按键按下
)cup发生中断,跳转到异常向量入口执行
)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:
)trap_init()函数构造异常向量
)vector_irq + stubs_offset 跳转,vector_irq用宏来实现
    a.保存寄存器的值
    b.asm_do_IRQ
    c.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.c
 trap_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    #        )
 THUMB(    nop            )
    W(b)    vector_und + stubs_offset        @这些都是异常向量
    W(ldr)    pc, .LCvswi + stubs_offset
    W(b)    vector_pabt + stubs_offset
    W(b)    vector_dabt + stubs_offset
    W(b)    vector_addrexcptn + stubs_offset
    W(b)    vector_irq + stubs_offset
    W(b)    vector_fiq + stubs_offset
　　......
----------------------------------------------
 3)分析vector_und
 vector_und由vector_stub宏定义而来
 vector_stub und, UND_MODE
---------------------------------------------------------
 //宏定义
     .macro    vector_stub, name, mode, correction=
    .align    

vector_\name:
    .if \correction
    sub    lr, lr, #\correction
    .endif
　　......

//替换后
     .macro    vector_stub, name, mode, correction=
    .align    

vector_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, lr
    mrs    lr, spsr
    str    lr, [sp, #]        @ save spsr

    @
    @ Prepare for SVC32 mode.  IRQs remain disabled.
    @
    mrs    r0, cpsr
    eor    r0, r0, #(\mode ^ SVC_MODE | PSR_ISETSTATE)
    msr    spsr_cxsf, r0

    .......    

    .endm

-------------------------------------------------------------
4)
    .long    __und_usr            @   (USR_26 / USR_32) //作用：保存寄存器，做处理，恢复寄存器
    .long    __und_invalid            @   (FIQ_26 / FIQ_32)
    .long    __und_invalid            @   (IRQ_26 / IRQ_32)
    .long    __und_svc            @   (SVC_26 / SVC_32)
    .long    __und_invalid            @
    .long    __und_invalid            @
    .long    __und_invalid            @
    .long    __und_invalid            @
    .long    __und_invalid            @
    .long    __und_invalid            @
    .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
-----------------------------------------------------------------
==========================================================================  
 
分析vector_irq
1)W(b)    vector_irq + stubs_offset
-----------------------------------------------------------------
2)vector_stub    irq, IRQ_MODE,
替换后
    .macro    vector_stub, name, mode, correction=
    .align    

vector_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, lr
    mrs    lr, spsr
    str    lr, [sp, #]        @ save spsr

    @
    @ Prepare for SVC32 mode.  IRQs remain disabled.
    @
    mrs    r0, cpsr
    eor    r0, r0, #(\mode ^ SVC_MODE | PSR_ISETSTATE)
    msr    spsr_cxsf, r0

    @
    @ the branch table must immediately follow this code
    @
    and    lr, lr, #0x0f
 THUMB(    adr    r0, 1f            )
 THUMB(    ldr    lr, [r0, lr, lsl #]    )
    mov    r0, sp
 ARM(    ldr    lr, [pc, lr, lsl #]    )
    movs    pc, lr            @ branch to handler in SVC mode
ENDPROC(vector_\name)

    .align
    @ handler addresses follow this label
:
    .endm
-----------------------------------------------------------

3)
    .long    __irq_usr            @    (USR_26 / USR_32)
    .long    __irq_invalid            @    (FIQ_26 / FIQ_32)
    .long    __irq_invalid            @    (IRQ_26 / IRQ_32)
    .long    __irq_svc            @    (SVC_26 / SVC_32)
    .long    __irq_invalid            @
    .long    __irq_invalid            @
    .long    __irq_invalid            @
    .long    __irq_invalid            @
    .long    __irq_invalid            @
    .long    __irq_invalid            @
    .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_check

    get_thread_info tsk
#ifdef CONFIG_PREEMPT
    ldr    r8, [tsk, #TI_PREEMPT]        @ get preempt count
    add    r7, r8, #            @ increment it
    str    r7, [tsk, #TI_PREEMPT]
#endif

    irq_handler                @处理函数
#ifdef CONFIG_PREEMPT
    ldr    r0, [tsk, #TI_PREEMPT]
    str    r8, [tsk, #TI_PREEMPT]
    teq    r0, r7
 ARM(    strne    r0, [r0, -r0]    )
 THUMB(    movne    r0, #        )
 THUMB(    strne    r0, [r0]    )
#endif
#ifdef CONFIG_TRACE_IRQFLAGS
    bl    trace_hardirqs_on
#endif

    mov    why, #
    b    ret_to_user
 UNWIND(.fnend        )
ENDPROC(__irq_usr)

    .ltorg

    .align
------------------------------------------------------
usr_entry分析：
    .macro    usr_entry
 UNWIND(.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 avoidance
    mov    r4, #-            @  ""  ""     ""        ""

    str    r1, [sp]        @ save the "real" r0 copied
                    @ from the exception stack

......

    .endm
------------------------------------------------------------
irq_handler分析：
    .macro    irq_handler
    get_irqnr_preamble r5, lr
:    get_irqnr_and_base r0, r6, r5, lr
    movne    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

......

    .endm
5) 调用asm_do_IRQ C处理程序