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）

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_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    #0        )

 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=0

    .align    5



vector_\name:

    .if \correction

    sub    lr, lr, #\correction

    .endif

　　......

//替换后    

     .macro    vector_stub, name, mode, correction=0

    .align    5 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, #8]        @ 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            @  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    5



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, #8]        @ 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 #2]    )

    mov    r0, sp

 ARM(    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_check



    get_thread_info tsk

#ifdef CONFIG_PREEMPT

    ldr    r8, [tsk, #TI_PREEMPT]        @ get preempt count

    add    r7, r8, #1            @ 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, #0        )

 THUMB(    strne    r0, [r0]    )

#endif

#ifdef CONFIG_TRACE_IRQFLAGS

    bl    trace_hardirqs_on

#endif



    mov    why, #0

    b    ret_to_user

 UNWIND(.fnend        )

ENDPROC(__irq_usr)



    .ltorg



    .align    5

------------------------------------------------------ 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, #-1            @  ""  ""     ""        ""



    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

1:    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