linux-2.6.26内核中ARM中断实现详解(2)

际上等于72

stmib sp, {r1 - 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

@

@ We are now ready to fill in the remaining blanks on the stack:

@

@ r2 - lr_, already fixed up for correct return/restart

@ r3 - spsr_

@ r4 - orig_r0 (see pt_regs definition in ptrace.h)

@

@ Also, separately save sp_usr and lr_usr

@

stmia r0, {r2 - r4}

stmdb r0, {sp, lr}^

@

@ Enable the alignment trap while in kernel mode

@

alignment_trap r0

@

@ Clear FP to mark the first stack frame

@

zero_fp

.endm

上面的这段代码主要在填充结构体pt_regs ，这里提到的struct pt_regs，在include/asm/ptrace.h中定义。此时sp指向struct pt_regs。

struct pt_regs {

long uregs[18];

};

#define ARM_cpsr uregs[16]

#define ARM_pc uregs[15]

#define ARM_lr uregs[14]

#define ARM_sp uregs[13]

#define ARM_ip uregs[12]

#define ARM_fp uregs[11]

#define ARM_r10 uregs[10]

#define ARM_r9 uregs[9]

#define ARM_r8 uregs[8]

#define ARM_r7 uregs[7]

#define ARM_r6 uregs[6]

#define ARM_r5 uregs[5]

#define ARM_r4 uregs[4]

#define ARM_r3 uregs[3]

#define ARM_r2 uregs[2]

#define ARM_r1 uregs[1]

#define ARM_r0 uregs[0]

#define ARM_ORIG_r0 uregs[17]

3.4 irq_handler的实现过程，archarmkernelentry-armv.S

.macro irq_handler

get_irqnr_preamble r5, lr

@在include/asm/arch-s3c2410/entry-macro.s中定义了宏get_irqnr_preamble为空操作，什么都不做

1: get_irqnr_and_base r0, r6, r5, lr @判断中断号，通过R0返回，3.5节有实现过程

movne r1, sp

@

@ routine called with r0 = irq number, r1 = struct pt_regs *

@

adrne lr, 1b

bne asm_do_IRQ @进入中断处理。

……

.endm

3.5 get_irqnr_and_base中断号判断过程，include/asm/arch-s3c2410/entry-macro.s

.macro get_irqnr_and_base, irqnr, irqstat, base, tmp

mov base, #S3C24XX_VA_IRQ

@@ try the interrupt offset register, since it is there

ldr irqstat, [ base, #INTPND ]

teq irqstat, #0

beq 1002f

ldr irqnr, [ base, #INTOFFSET ] @通过判断INTOFFSET寄存器得到中断位置

mov tmp, #1

tst irqstat, tmp, lsl irqnr

bne 1001f

@@ the number specified is not a valid irq, so try

@@ and work it out for ourselves

mov irqnr, #0 @@ start here

@@ work out which irq (if any) we got

movs tmp, irqstat, lsl#16

addeq irqnr, irqnr, #16

moveq irqstat, irqstat, lsr#16

tst irqstat, #0xff

addeq irqnr, irqnr, #8

moveq irqstat, irqstat, lsr#8

tst irqstat, #0xf

addeq irqnr, irqnr, #4

moveq irqstat, irqstat, lsr#4

tst irqstat, #0x3

addeq irqnr, irqnr, #2

moveq irqstat, irqstat, lsr#2

tst irqstat, #0x1

addeq irqnr, irqnr, #1

@@ we have the value

1001:

adds irqnr, irqnr, #IRQ_EINT0 @加上中断号的基准数值，得到最终的中断号，注意：此时没有考虑子中断的具体情况，(子中断的问题后面会有讲解)。IRQ_EINT0在include/asm/arch-s3c2410/irqs.h中定义.从这里可以看出，中断号的具体值是有平台相关的代码决定的，和硬件中断挂起寄存器中的中断号是不等的。

1002:

@@ exit here, Z flag unset if IRQ

.endm

3.6 asm_do_IRQ实现过程，arch/arm/kernel/irq.c

asmlinkage void __exception asm_do_IRQ(unsigned int irq, struct pt_regs *regs)

{

struct pt_regs *old_regs = set_irq_regs(regs);

struct irq_desc *desc = irq_desc + irq;//根据中断号找到对应的irq_desc

/*

* Some hardware gives randomly wrong interrupts. Rather

* than crashing, do something sensible.

*/

if (irq >= NR_IRQS)

desc = bad_irq_desc;

irq_enter();//没做什么特别的工作，可以跳过不看

desc_handle_irq(irq, desc);// 根据中断号和desc进入中断处理

/* AT91 specific workaround */

irq_finish(irq);

irq_exit();

set_irq_regs(old_regs);

}

static inline void desc_handle_irq(unsigned int irq, struct irq_desc *desc)

{

desc->handle_irq(irq, desc);//中断处理

}

上述asmlinkage void __exception asm_do_IRQ(unsigned int irq, struct pt_regs *regs)使用了asmlinkage标识。那么这个标识的含义如何理解呢?

该符号定义在kernel/include/linux/linkage.h中