GNU ARM汇编--(四)中断汇编之非嵌套中断处理

在写这篇blog之前,不得不感慨一句:纸上得来终觉浅,绝知此事要躬行.作为EE出身的,虽然好久好久没用汇编写单片机的中断了,但自我感觉对中断的理解还是比较深入的,本以为在GNU ARM汇编下搞个中断会很容易,谁知道断断续续花了我几周.完全用汇编写中断和用c中的_irq写中断还是有区别的,谁用谁知道.还是那句话:深入细节是必须的,也是值得的.

这一篇blog的理论知识主要来源于:《ARM System Developers Guide》.

ARM的异常和相应的模式之间的对应关系见下表:

当一个异常导致模式的改变时,内核自动地:

1、把cpsr保存到相应模式下的spsr

2、把pc保存到相应模式下的lr

3、设置cpsr为相应异常模式

4、设置pc为相应异常处理程序的入口地址

从异常中断处理程序返回包含下面两个操作:

1、从spsr_mode中恢复内容到cpsr中

2、从lr_mode中恢复内容到pc中,返回到异常中断的指令的下一条政令处执行.

上面刚提到了异常发生时内核的一些动作,那对与IRQ或者FIQ而言,还多一项变化:禁用相关的中断IRQ或FIQ,禁止同类型的其他中断被触发.

对于最简单的非嵌套中断处理的处理流程如下:

下面给出汇编代码:

[cpp]view plaincopy

1. /*
2. simpleinterruption
3. copyleft@dndxhej@gmail.com
4. */
6. .equNOINT,0xc0
7. .equWTCON,0x53000000
8. .equGPBCON,0x56000010@led
9. .equGPBDAT,0x56000014@led
10. .equGPBUP,0x56000018@led
11. .equGPFCON,0x56000050@interruptconfig
12. .equEINTMASK,0x560000a4
13. .equEXTINT0,0x56000088
14. .equEXTINT1,0x5600008c
15. .equEXTINT2,0x56000090
16. .equINTMSK,0x4A000008
17. .equEINTPEND,0x560000a8
19. .equINTSUBMSK,0X4A00001C
21. .equSRCPND,0X4A000000
22. .equINTPND,0X4A000010
24. .global_start
25. _start:breset
26. ldrpc,_undefined_instruction
27. ldrpc,_software_interrupt
28. ldrpc,_prefetch_abort
29. ldrpc,_data_abort
30. ldrpc,_not_used
31. @birq
32. ldrpc,_irq
33. ldrpc,_fiq
37. _undefined_instruction:.wordundefined_instruction
38. _software_interrupt:.wordsoftware_interrupt
39. _prefetch_abort:.wordprefetch_abort
40. _data_abort:.worddata_abort
41. _not_used:.wordnot_used
42. _irq:.wordirq
43. _fiq:.wordfiq
45. .balignl16,0xdeadbeef
47. reset:
50. ldrr3,=WTCON
51. movr4,#0x0
52. strr4,[r3]@disablewatchdog
54. ldrr0,=GPBCON
55. ldrr1,=0x15400
56. strr1,[r0]
58. ldrr2,=GPBDAT
59. ldrr1,=0x160
60. strr1,[r2]
62. bldelay
65. msrcpsr_c,#0xd2@进入中断模式
66. ldrsp,=3072@中断模式的栈指针定义
68. msrcpsr_c,#0xdf@进入系统模式
69. ldrsp,=4096@设置系统模式的栈指针
74. @--------------------------------------------
76. ldrr0,=GPBUP
77. ldrr1,=0x03f0
78. strr1,[r0]
82. ldrr0,=GPFCON
83. ldrr1,=0x2ea@0x2
84. strr1,[r0]
86. ldrr0,=EXTINT0
87. ldrr1,=0x8f888@0x0@0x8f888@~(7|(7<4)|(7<8)|(7<16))
88. strr1,[r0]
90. ldrr0,=EINTPEND
91. ldrr1,=0xf0@0b10000
92. strr1,[r0]
94. ldrr0,=EINTMASK
95. ldrr1,=0x00@0b00000
96. strr1,[r0]
100. ldrr0,=SRCPND
101. ldrr1,=0xff@0x1@0b11111
102. strr1,[r0]
104. ldrr0,=INTPND
105. ldrr1,=0xff@0x1@0b11111
106. strr1,[r0]
108. ldrr0,=INTMSK
109. ldrr1,=0xffffff00@0b00000
110. strr1,[r0]
112. MRSr1,cpsr
113. BICr1,r1,#0x80
114. MSRcpsr_c,r1
117. blmain
119. irq:
120. sublr,lr,#4
121. stmfdsp!,{r0-r12,lr}
122. blirq_isr
123. ldmfdsp!,{r0-r12,pc}^
127. irq_isr:
131. ldrr2,=GPBDAT
132. ldrr1,=0x0e0
133. strr1,[r2]
136. ldrr0,=EINTPEND
137. ldrr1,=0xf0
138. strr1,[r0]
140. ldrr0,=SRCPND
141. ldrr1,=0x3f@0b11111
142. strr1,[r0]
146. ldrr0,=INTPND
147. ldrr1,=0x3f@0b11111
148. strr1,[r0]
152. movpc,lr
155. delay:
157. ldrr3,=0xffff
159. delay1:
160. subr3,r3,#1
162. cmpr3,#0x0
164. bnedelay1
166. movpc,lr
171. main:
172. ledloop:
174. ldrr1,=0x1c0
175. strr1,[r2]
176. bldelay
178. ldrr1,=0x1a0
179. strr1,[r2]
180. bldelay
182. ldrr1,=0x160
183. strr1,[r2]
184. bldelay
186. ldrr1,=0x0e0
187. strr1,[r2]
188. bldelay
191. bledloop
196. undefined_instruction:
197. nop
198. software_interrupt:
199. nop
200. prefetch_abort:
201. nop
202. data_abort:
203. nop
204. not_used:
205. nop
206. fiq:
207. nop

[cpp]view plaincopy

1. OUTPUT_FORMAT("elf32-littlearm","elf32-littlearm","elf32-littlearm")
2. OUTPUT_ARCH(arm)
3. ENTRY(_start)
5. SECTIONS{
6. .=0x00000000;
7. .text:{
8. *(.text)
9. *(.rodata)
10. }
12. .dataALIGN(4):{
13. *(.data)
14. }
16. .bssALIGN(4):{
17. *(.bss)
18. }
19. }

[cpp]view plaincopy

1. CROSS=arm-linux-
2. CFLAGS=-nostdlib
4. int.bin:start.S
5. ${CROSS}gcc$(CFLAGS)-c-ostart.ostart.S
6. ${CROSS}ld-Tint.ldsstart.o-oint.elf
7. #${CROSS}ld-Ttext-segment0x30000000start.o-oint.elf
8. ${CROSS}objcopy-Obinary-Sint.elfint.bin
9. #rm-f*.o
12. clean:
13. rm-f*.elf*.o
14. rm-fint.bin

该程序实现的流水灯,然后四个按键可以实现外部中断.

代码中值得注意的地方有几点:

1、lds文件中的地址配为0x00000000,因为程序是download到nandflash中运行的.最开始这里写的是0x300