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_
ame:
.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_
ame)
.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