GNU ARM汇编--(五)中断汇编之嵌套中断处理
在上篇《GNU ARM汇编--(四)中断汇编之非嵌套中断处理》中分析了最简单的中断处理的写法,再看TQ2440启动代码中的中断向量表的写法就一目了然了.今天抽时间对嵌套中断处理的学习做下整理.
嵌套中断处理的核心代码如下:
;/* ; * ____________________________________________________________________ ; * ; * Copyright (c) 2004, Andrew N. Sloss, Chris Wright and Dominic Symes ; * All rights reserved. ; * ____________________________________________________________________ ; * ; * NON-COMMERCIAL USE License ; * ; * Redistribution and use in source and binary forms, with or without ; * modification, are permitted provided that the following conditions ; * are met: ; * ; * 1. For NON-COMMERCIAL USE only. ; * ; * 2. Redistributions of source code must retain the above copyright ; * notice, this list of conditions and the following disclaimer. ; * ; * 3. Redistributions in binary form must reproduce the above ; * copyright notice, this list of conditions and the following ; * disclaimer in the documentation and/or other materials provided ; * with the distribution. ; * ; * 4. All advertising materials mentioning features or use of this ; * software must display the following acknowledgement: ; * ; * This product includes software developed by Andrew N. Sloss, ; * Chris Wright and Dominic Symes. ; * ; * THIS SOFTWARE IS PROVIDED BY THE CONTRIBUTORS ``AS IS'' AND ANY ; * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE ; * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR ; * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE ; * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, ; * OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, ; * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, ; * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY ; * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR ; * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT ; * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY ; * OF SUCH DAMAGE. ; * ; * If you have questions about this license or would like a different ; * license please email : ; * ; * [email protected] ; * ; * ; */ ;/*********************************************************************** ; * ; * Module : nih9_9.s ; * Descriptions : Nested Interrupt Handler ; * Example : 9.9 ; * OS : generic ; * Platform : generic ; * History : ; * ; * 31th December 2003 ; * - added header ; * ; ***********************************************************************/ EXPORT nestedInterruptHandler Maskmd EQU 0x1f ; processor mode mask SVC32md EQU 0x13 ; SVC mode I_Bit EQU 0x80 ; IRQ bit FRAME_R0 EQU 0x00 FRAME_R1 EQU FRAME_R0+4 FRAME_R2 EQU FRAME_R1+4 FRAME_R3 EQU FRAME_R2+4 FRAME_R4 EQU FRAME_R3+4 FRAME_R5 EQU FRAME_R4+4 FRAME_R6 EQU FRAME_R5+4 FRAME_R7 EQU FRAME_R6+4 FRAME_R8 EQU FRAME_R7+4 FRAME_R9 EQU FRAME_R8+4 FRAME_R10 EQU FRAME_R9+4 FRAME_R11 EQU FRAME_R10+4 FRAME_R12 EQU FRAME_R11+4 FRAME_PSR EQU FRAME_R12+4 FRAME_LR EQU FRAME_PSR+4 FRAME_PC EQU FRAME_LR+4 FRAME_SIZE EQU FRAME_PC+4 AREA nih9_9,CODE,readonly nestedInterruptHandler ; instruction state : comment SUB r14,r14,#4 ; 2 : STMDB r13!,{r0-r3,r12,r14} ; 2 : save context ; <insert code here> BL read_RescheduleFlag ; 3 : more processing CMP r0,#0 ; 3 : if processing? LDMNEIA r13!,{r0-r3,r12,pc}^ ; 4 : then return MRS r2,SPSR ; 5 : copy SPSR_irq MOV r0,r13 ; 5 : copy r13_irq ADD r13,r13,#6*4 ; 5 : reset stack MRS r1,CPSR ; 6 : copy CPSR BIC r1,r1,#Maskmd ; 6 : ORR r1,r1,#SVC32md ; 6 : MSR CPSR_c,r1 ; 6 : change SVC mode SUB r13,r13,#FRAME_SIZE-FRAME_R4 ; 7 : make stack space STMIA r13,{r4-r11} ; 7 : save r4-r11 LDMIA r0,{r4-r9} ; 7 : r4-r9 IRQ stack BIC r1,r1,#I_Bit ; 8 : MSR CPSR_c,r1 ; 8 : enable int STMDB r13!,{r4-r7} ; 9 : save r4-r7 SVC STR r2,[r13,#FRAME_PSR] ; 9 : save PSR STR r8,[r13,#FRAME_R12] ; 9 : save r12 STR r9,[r13,#FRAME_PC] ; 9 : save pc STR r14,[r13,#FRAME_LR] ; 9 : save lr ; <insert code here> LDMIA r13!,{r0-r12,r14} ; 11 : restore context MSR SPSR_cxsf,r14 ; 11 : restore SPSR LDMIA r13!,{r14,pc}^ ; 11 : return read_RescheduleFlag ; <implement your own reschedule flag code here> MOV r0,#0 ; more processing MOV pc,r14 ; return END
代码的关键就是在中断后切换到SVC模式下,利用svc mode的stack来实现中断嵌套过程的备份以及恢复操作.从代码中可以看到,从R0到PC都在栈中有备份,这里我们叫栈帧.记得《深入理解计算机系统》一书在讲x86汇编的函数调用时也是栈帧的概念.这点上中断嵌套和函数调用有相似之处.有了这个栈帧,利用压栈出栈操作就一切ok了.
刚看这个代码,对有个地方有疑问,就是觉得中断开早了:
BIC r1,r1,#I_Bit ; 8 :
MSR CPSR_c,r1 ; 8 : enable int
STMDB r13!,{r4-r7} ; 9 : save r4-r7 SVC
STR r2,[r13,#FRAME_PSR] ; 9 : save PSR
STR r8,[r13,#FRAME_R12] ; 9 : save r12
STR r9,[r13,#FRAME_PC] ; 9 : save pc
STR r14,[r13,#FRAME_LR] ; 9 : save lr
觉得开中断的代码应该放在后面,这样才能保证svc mode下的stack frame不会被破坏.但在草稿纸上画一下irq和svc下的stack图,就发现堆栈操作并没有问题.可以假设刚开中断立马就有新的中断了,r4-r7 r8 r9都有在STMIA r13,{r4-r11} 中保存到svc的stack中,LDMIA r0,{r4-r9} 和STMDB r13!,{r4-r7} 保证了最初的r0-r3在栈中,而LDMIA r0,{r4-r9}和STR r8,[r13,#FRAME_R12] 以及STR r9,[r13,#FRAME_PC] 保证了R12和PC,保证正确返回.(这里的r9装的是r14_irq,所以pc就是r14_irq,这样就保证了从中断服务例程中返回).至于STR r14,[r13,#FRAME_LR]中的r14是r14_svc,将其压入svc的stack中,中断例程用bl就不会出现错误了,在最后LDMIA r13!,{r14,pc}^ 中r14得到恢复.而r2保存的是spsr,也就是svc模式的状态,一直不变,不用担心会被覆盖.
最后,再看了一遍图,觉得r10和r11的帧可以省去,因为r4-r9是用来存atpcs的r0-r3,r12,r14,而r10和r11用不到.貌似可以省点空间和时间,具体的待会实验一下.
下面给出实际的嵌套中断处理,利用r10来保存INTOFFSET的值,根据该值来判定是什么中断,从而做不同的处理.具体的效果是:代码会做流水灯的动作,Key1代表INT1,中断处理动作是4个灯全全亮然后全灭,Key4代表代表INT0,中断处理动作是第一个灯和第三个灯亮,然后第二个灯和第四个灯亮.
/* simple interruption copyleft@[email protected] */ .equ Maskmd, 0x1f @ processor mode mask .equ SVC32md, 0x13 @ SVC mode .equ I_Bit, 0x80 @ IRQ bit .equ FRAME_R0, 0x00 .equ FRAME_R1, FRAME_R0+4 .equ FRAME_R2, FRAME_R1+4 .equ FRAME_R3, FRAME_R2+4 .equ FRAME_R4, FRAME_R3+4 .equ FRAME_R5, FRAME_R4+4 .equ FRAME_R6, FRAME_R5+4 .equ FRAME_R7, FRAME_R6+4 .equ FRAME_R8, FRAME_R7+4 .equ FRAME_R9, FRAME_R8+4 .equ FRAME_R10, FRAME_R9+4 .equ FRAME_R11, FRAME_R10+4 .equ FRAME_R12, FRAME_R11+4 .equ FRAME_PSR, FRAME_R12+4 .equ FRAME_LR, FRAME_PSR+4 .equ FRAME_PC, FRAME_LR+4 .equ FRAME_SIZE, FRAME_PC+4 .equ NOINT, 0xc0 .equ WTCON, 0x53000000 .equ GPBCON, 0x56000010 @led .equ GPBDAT, 0x56000014 @led .equ GPBUP, 0x56000018 @led .equ GPFCON, 0x56000050 @interrupt config .equ EINTMASK, 0x560000a4 .equ EXTINT0, 0x56000088 .equ EXTINT1, 0x5600008c .equ EXTINT2, 0x56000090 .equ INTMSK, 0x4A000008 .equ EINTPEND, 0x560000a8 .equ INTSUBMSK, 0X4A00001C .equ SRCPND, 0X4A000000 .equ INTPND, 0X4A000010 .equ INTOFFSET, 0x4A000014 .global _start _start: b reset ldr pc, _undefined_instruction ldr pc, _software_interrupt ldr pc, _prefetch_abort ldr pc, _data_abort ldr pc, _not_used @b irq ldr pc, _irq ldr pc, _fiq _undefined_instruction: .word undefined_instruction _software_interrupt: .word software_interrupt _prefetch_abort: .word prefetch_abort _data_abort: .word data_abort _not_used: .word not_used _irq: .word irq _fiq: .word fiq .balignl 16,0xdeadbeef reset: ldr r3, =WTCON mov r4, #0x0 str r4, [r3] @ disable watchdog ldr r0, =GPBCON ldr r1, =0x15400 str r1, [r0] ldr r2, =GPBDAT ldr r1, =0x160 str r1, [r2] bl delay msr cpsr_c, #0xd2 @进入中断模式 ldr sp, =0xc00 @中断模式的栈指针定义 msr cpsr_c, #0xd3 @进入svc模式 ldr sp, =0xfff @设置svc模式的栈指针 @-------------------------------------------- ldr r0, =GPBUP ldr r1, =0x03f0 str r1, [r0] ldr r0, =GPFCON ldr r1, =0x2ea@0x2 str r1, [r0] ldr r0, =EXTINT0 @ldr r1, =0x8f888@0x0@0x8f888 @~(7|(7<<4)|(7<<8)|(7<<16)) ldr r1, =0xafaaa str r1, [r0] ldr r0, =EINTPEND ldr r1, =0xf0@0b10000 str r1, [r0] ldr r0, =EINTMASK ldr r1, =0x00@0b00000 str r1, [r0] ldr r0, =SRCPND ldr r1, =0xff@0x1@0b11111 str r1, [r0] ldr r0, =INTPND ldr r1, =0xff@0x1@0b11111 str r1, [r0] ldr r0, =INTMSK ldr r1, =0xffffff00@0b00000 str r1, [r0] MRS r1, cpsr BIC r1, r1, #0x80 MSR cpsr_c, r1 bl main irq: sub r14,r14,#4 @ 2 : stmdb sp!,{r0-r3,r12,r14} @ 2 : save context @ <insert code here> @BL read_RescheduleFlag @ 3 : more processing @CMP r0,#0 @ 3 : if processing? @LDMNEIA sp!,{r0-r3,r12,pc}^ @ 4 : then return @@@@@@@@@@@@@@@@ ldr r10,=INTOFFSET @用r10保存中断的offset ldr r10,[r10] ldr r0,=EINTPEND ldr r1,=0xf0 str r1,[r0] ldr r0, =SRCPND ldr r1, =0x3f@0b11111 str r1, [r0] ldr r0, =INTPND ldr r1, =0x3f@0b11111 str r1, [r0] @@@@@@@@@@@@@@ mrs r2,SPSR @ 5 : copy SPSR_irq mov r0,sp @ 5 : copy sp_irq add sp,sp,#6*4 @ 5 : reset stack mrs r1,CPSR @ 6 : copy CPSR bic r1,r1,#Maskmd @ 6 : orr r1,r1,#SVC32md @ 6 : msr CPSR_c,r1 @ 6 : change SVC mode sub sp,sp,#FRAME_SIZE-FRAME_R4 @ 7 : make stack space stmia sp,{r4-r11} @ 7 : save r4-r11 ldmia r0,{r4-r9} @ 7 : r4-r9 IRQ stack bic r1,r1,#I_Bit @ 8 : msr CPSR_c,r1 @ 8 : enable int stmdb sp!,{r4-r7} @ 9 : save r4-r7 SVC str r2,[sp,#FRAME_PSR] @ 9 : save PSR str r8,[sp,#FRAME_R12] @ 9 : save r12 str r9,[sp,#FRAME_PC] @ 9 : save pc str r14,[sp,#FRAME_LR] @ 9 : save lr @ <insert code here> @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ cmp r10,#0x0 bleq blink1 cmp r10,#0x1 bleq blink3 @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ LDMIA sp!,{r0-r12,r14} @ 11 : restore context MSR SPSR_cxsf,r14 @ 11 : restore SPSR LDMIA sp!,{r14,pc}^ @ 11 : return delay: ldr r3,=0xffff delay1: sub r3,r3,#1 cmp r3,#0x0 bne delay1 mov pc,lr blink1: ldr r0, =GPBDAT ldr r1, =0x000 str r1, [r0] ldr r3,=0xffff delay2: sub r3,r3,#1 cmp r3,#0x0 bne delay2 ldr r0, =GPBDAT ldr r1, =0x1f0 str r1, [r0] ldr r3,=0xffff delay3: sub r3,r3,#1 cmp r3,#0x0 bne delay3 mov pc,lr blink2: ldr r0, =GPBDAT ldr r1, =0x140 str r1, [r0] ldr r3,=0xffff delay12: sub r3,r3,#1 cmp r3,#0x0 bne delay12 ldr r0, =GPBDAT ldr r1, =0xa0 str r1, [r0] ldr r3,=0xffff delay13: sub r3,r3,#1 cmp r3,#0x0 bne delay13 mov pc,lr blink3: ldr r0, =GPBDAT ldr r1, =0x0a0 str r1, [r0] stmfd sp!,{lr} bl delay ldr r0, =GPBDAT ldr r1, =0x140 str r1, [r0] bl delay ldmfd sp!,{lr} mov pc,lr main: ledloop: ldr r1,=0x1c0 str r1,[r2] bl delay ldr r1,=0x1a0 str r1,[r2] bl delay ldr r1,=0x160 str r1,[r2] bl delay ldr r1,=0x0e0 str r1,[r2] bl delay b ledloop undefined_instruction: nop software_interrupt: nop prefetch_abort: nop data_abort: nop not_used: nop fiq: nop
代码比较繁琐,有几点值得注意:在嵌套中断处理中,压栈后先保存INTOFFSET的值,再清中断(SRCPND和INTPND).因为SRCPND和INTPND清除后INTOFFSET就自动清除了,所以要先保存.在中断服务程序中,是可以用bl跳转到各自的中断服务程序的,比如blne blink1和blne blink3,值得对比的blink1和blink3,他们的不同在于blink1自己用代码做了延时,而blink3是调用bl delay做的延时,那么这个时候要注意的就是lr的push和pop操作,不然lr就被覆盖了,程序不能正确返回了.
注意了以上两点,程序上达到了嵌套处理的效果.因为采用的是下降边沿触发,而按键没有防抖处理,有时候单按一个键就有嵌套中断了.最后总结一下这种处理的优缺点:优点是在为一个中断处理服务完成前允许其它中断,以缩短中断延迟;而缺点是不处理中断的优先级,因此低优先级的中断会阻塞高优先级的中断.