Abstract
Qsys其中之一的卖点就是允许你建立hierarchical的subsystem。在SOC设计中，通常我们会将慢速的周边使用较慢的clock而自成一个系统，在Qsys中允许我们将这些较慢的周边包成一个peripheral subsystem，而不是像SOPC Builder一样只能有一个system。当我们使用subsystem的架构时，该如何让subsystem内IP使用interrupt的方式与Nios II沟通呢?

Introduction
使用环境：Windows XP SP3 + VirtualBox 4.1.2 + Quartus II 11.0

本文将讨论以下主题：

1.如何使用IRQ Bridge连接subsystem的IRQ export到Nios II Processor?

2.如何避开Nios II SBT目前无法自动产生IRQ number常数在system.h的bug?

3.如何在App project使用Interrupt?

1.如何使用IRQ Bridge连接subsystem的IRQ export到Nios II Processor?

根据[1] Qsys Interconnect p.7-27 IRQ Bridge章节的建议，若要在subsystem使用interrupt，必须在包含Nios II的CPU subsystem使用IRQ Bridge接收Peripheral subsystem所export出来的IRQ，然后才连到Nios II Processor。至于下图中的Merlin IRQ Mapper则并不是必需的，若你在CPU subsystem中也有IP要使用interrupt，这必须再包一层Merlin IRQ Mapper；若你在CPU subsystem没有IP要使用interrupt，只有Peripheral subsystem使用interrupt，可以直接只使用IRQ Bridge连接到Nios II Processor。

常见的错误(也是我第一次的错误)是直接将Peripheral subsystem所export的IRQ直接连到Nios II Processor，这样Qsys与Quartus II编译都没有任何错误，Nios II也没有错误，不过Nios II的C code将收不到来自Peripheral subsystem的interrupt。

2.如何避开Nios II SBT目前无法自动产生IRQ number常数在system.h的bug?

除此之外，在[2] Quartus II 11.0 Release Notes的p.15已经承认在Quartus II 11.0有以下的bug。

简单的说，就是若你在subsystem中使用interrupt，当你使用Generate BSP时，Nios II SBT根据*.sopcinfo在system.h所产生相对应的IRQ number常数，永远都是-1，并无法反应出目前硬件架构中真正的IRQ number。且经过实测，这个问题在Quartus II 11.1也依然存在。

如图所示，我们对push button使用interrupt，但在system.h的PERIPHERAL_SYSTEM_BUTTON_PIO_IRQ常数却是-1，与在Qsys上的IRQ number不同。

这会造成什么影响呢?只要你的App project使用到有使用interrupt的IP，编译就会产生错误，如下图我们在system timer有使用interrupt，所以一编译就产生错误无法继续。

详细错误讯息如下：

Error: Interrupt not connected for peripheral_system_timer_0. The system clock driver requires an interrupt to be connected. Please select an IRQ for this device in SOPC builder.

root cause就是system.h的IRQ number都是-1，所以App project找不到该IP的IRQ number而无法编译。

Solution
既然在system.h的IRQ number都是-1，我们只好重新自己在system.h手动定义IRQ number。根据[3] Altera Wiki : New Qsys Issues for Interrupts的建议

当然你可以直接去修改system.h，但别忘了BSP project的所有档案最好不要手动修改，应该交由Nios II SBT或者command line script去修改才对，因为每当你执行Generate BSP或者BSP Editor时，Nios II SBT都会重新产生system.h，也就是你做的所有修改都会被覆盖掉。所以[3] Altera Wiki : New Qsys Issues for Interrupts 的解法虽然可行，但并不完美。

根据 [2] Quartus II 11.0 Release Notes的建议

看起来是要我们自己另开一个my_system.h，然后将system.h所有内容复制到system.h，自己在my_system.h加上IRQ number常数，并且App project也使用my_system.h，这样Generate BSP与BSP Editor就不会改到我的my_system.h了。

这样看似理想，但却衍生另外一个问题：BSP project有大量的档案都include "system.h"，你必须手动一一的改成include "my_system.h"，这也是个大工程。所以[2] Quartus II 11.0 Release Notes 看似也不尽理想。

我在此提供一个小技巧对付Nios II SBT目前这个bug。

在system.h的尾部自己加上IP IRQ number的定义如下图，先执行#undef取消这个常数的定义，再用#define重新这个常数，因为若同一个常数在system.h重复#define，会产生warning，若使用#undef就完全没有warning。

然后将这些#undef与#define另存一个文本文件，每当你执行Generate BSP或者BSP Editor时，system.h就会被Nios II SBT重新产生盖掉你原先的设定，再将这些#undef与#define贴到system.h的最下方。如此就只需修改system.h，其他BSP档案都不用做任何修改。

如此修改重新编译后，就可顺利Build Project，没有任何错误。

3.如何在App project使用Interrupt?

根据[4] Exception Handling p.8-16与p.8-17的建议，我们将App project写成如下的code使用interrupt。

nios2_onchip_leg_push_button.c / C

1 /*
2 (C) OOMusou 2011 http://oomusou.cnblogs.com
3
4 Filename : nios2_onchip_led_push_button.c
5 Compiler : Nios II SBT 11.0
6 Description : test led, push_button & interrupt in subsystem
7 Release : Jan.06,2012 1.0
8 */
9
10 #include <stdio.h>
11 #include "system.h"
12 #include "alt_types.h"
13 #include "sys/alt_irq.h"
14 #include "altera_avalon_pio_regs.h"
15
16 volatile int edge_capture;
17
18 #ifdef ALT_ENHANCED_INTERRUPT_API_PRESENT
19 void handle_key_interrupts(void *context) {
20 #else
21 void handle_key_interrupts(void *context, alt_u32 id) {
22 #endif
23
24 volatile int *edge_capture_ptr = (volatile int*)context;
25 *edge_capture_ptr = IORD_ALTERA_AVALON_PIO_EDGE_CAP(PERIPHERAL_SYSTEM_BUTTON_PIO_BASE);
26 IOWR_ALTERA_AVALON_PIO_EDGE_CAP(PERIPHERAL_SYSTEM_BUTTON_PIO_BASE, 0);
27
28 if (edge_capture == 0x01) {
29 printf("key 1 pressed!\n");
30 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0xFE);
31 edge_capture = 0x00;
32 }
33 else if (edge_capture == 0x02) {
34 printf("key 2 pressed\n");
35 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0xFD);
36 edge_capture = 0x00;
37 }
38 else if (edge_capture == 0x04) {
39 printf("key 3 pressed\n");
40 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0xFB);
41 edge_capture = 0x00;
42 }
43 else if (edge_capture == 0x08) {
44 printf("key 4 pressed\n");
45 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0xF7);
46 edge_capture = 0x00;
47 }
48 else if (edge_capture == 0x10) {
49 printf("key 5 pressed\n");
50 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0xEF);
51 edge_capture = 0x00;
52 }
53 else if (edge_capture == 0x20) {
54 printf("key 6 pressed\n");
55 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0xDF);
56 edge_capture = 0x00;
57 }
58 else if (edge_capture == 0x40) {
59 printf("key 7 pressed\n");
60 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0xBF);
61 edge_capture = 0x00;
62 }
63 else if (edge_capture == 0x80) {
64 printf("key 8 pressed\n");
65 IOWR(PERIPHERAL_SYSTEM_LED_PIO_BASE, 0x00, 0x7F);
66 edge_capture = 0x00;
67 }
68 }
69
70
71 void init_key() {
72 void *edge_capture_ptr = (void *)&edge_capture;
73 IOWR_ALTERA_AVALON_PIO_IRQ_MASK(PERIPHERAL_SYSTEM_BUTTON_PIO_BASE, 0xFF);
74 IOWR_ALTERA_AVALON_PIO_EDGE_CAP(PERIPHERAL_SYSTEM_BUTTON_PIO_BASE, 0x0);
75
76 #ifdef ALT_ENHANCED_INTERRUPT_API_PRESENT
77 alt_ic_isr_register(PERIPHERAL_SYSTEM_BUTTON_PIO_IRQ_INTERRUPT_CONTROLLER_ID,
78 PERIPHERAL_SYSTEM_BUTTON_PIO_IRQ,
79 handle_key_interrupts,
80 edge_capture_ptr,
81 0x0);
82 #else
83
84 alt_irq_register(PERIPHERAL_SYSTEM_BUTTON_PIO_IRQ,
85 edge_capture_ptr,
86 handle_key_interrupts);
87 #endif
88 }
89
90
91 int main() {
92 printf("Nios II + Onchip + LED + Push Button Test!\n");
93
94 init_key();
95
96 while(1);
97
98 return 0;
99 }

以上的code我不打算一行一行讲解，详细请参考[4] Exception Handling p.8-16与p.8-17，我要强调的是，一般在使用interrupt时，Altera都会建议你使用新的alt_ic_isr_register()，而不要使用旧的alt_irq_register()，并且说未来Nios II SBT版本将只支持alt_ic_isr_register()，若在只有一层Qsys的system下，可以使用alt_ic_isr_register()没有问题，但在具有Qsys subsystem下使用interrupt时，若使用alt_ic_isr_register()将会造成编译错误，会说找不到alt_ic_isr_register()，为什么会这样呢?

在一般只有一层Qsys system，在system.h可以看到#define ALT_ENHANCED_INTERRUPT_API_PRESENT，如下图所示：

但在使用Qsys subsystem的system.h下，看不到#define ALT_ENHANCED_INTERRUPT_API_PRESENT

在BSP的

sys/alt_irq.h / C

1 #ifndef __ALT_IRQ_H__
2 #define __ALT_IRQ_H__
3
4 /******************************************************************************
5 * *
6 * License Agreement *
7 * *
8 * Copyright (c) 2009 Altera Corporation, San Jose, California, USA. *
9 * All rights reserved. *
10 * *
11 * Permission is hereby granted, free of charge, to any person obtaining a *
12 * copy of this software and associated documentation files (the "Software"), *
13 * to deal in the Software without restriction, including without limitation *
14 * the rights to use, copy, modify, merge, publish, distribute, sublicense, *
15 * and/or sell copies of the Software, and to permit persons to whom the *
16 * Software is furnished to do so, subject to the following conditions: *
17 * *
18 * The above copyright notice and this permission notice shall be included in *
19 * all copies or substantial portions of the Software. *
20 * *
21 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
22 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, *
23 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE *
24 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER *
25 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING *
26 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER *
27 * DEALINGS IN THE SOFTWARE. *
28 * *
29 * This agreement shall be governed in all respects by the laws of the State *
30 * of California and by the laws of the United States of America. *
31 * *
32 ******************************************************************************/
33
34 /*
35 * alt_irq.h is the Nios II specific implementation of the interrupt controller
36 * interface.
37 *
38 * Nios II includes optional support for an external interrupt controller.
39 * When an external controller is present, the "Enhanced" interrupt API
40 * must be used to manage individual interrupts. The enhanced API also
41 * supports the processor's internal interrupt controller. Certain API
42 * members are accessible from either the "legacy" or "enhanced" interrpt
43 * API.
44 *
45 * Regardless of which API is in use, this file should be included by
46 * application code and device drivers that register ISRs or manage interrpts.
47 */
48 #include <errno.h>
49
50 #include "nios2.h"
51 #include "alt_types.h"
52 #include "system.h"
53
54 #ifdef __cplusplus
55 extern "C"
56 {
57 #endif /* __cplusplus */
58
59 /*
60 * Macros used by alt_irq_enabled
61 */
62 #define ALT_IRQ_ENABLED 1
63 #define ALT_IRQ_DISABLED 0
64
65 /*
66 * Number of available interrupts in internal interrupt controller.
67 */
68 #define ALT_NIRQ NIOS2_NIRQ
69
70 /*
71 * Used by alt_irq_disable_all() and alt_irq_enable_all().
72 */
73 typedef int alt_irq_context;
74
75 /* ISR Prototype */
76 #ifdef ALT_ENHANCED_INTERRUPT_API_PRESENT
77 typedef void (*alt_isr_func)(void* isr_context);
78 #else
79 typedef void (*alt_isr_func)(void* isr_context, alt_u32 id);
80 #endif
81
82 /*
83 * The following protypes and routines are supported by both
84 * the enhanced and legacy interrupt APIs
85 */
86
87 /*
88 * alt_irq_enabled can be called to determine if the processor's global
89 * interrupt enable is asserted. The return value is zero if interrupts
90 * are disabled, and non-zero otherwise.
91 *
92 * Whether the internal or external interrupt controller is present,
93 * individual interrupts may still be disabled. Use the other API to query
94 * a specific interrupt.
95 */
96 static ALT_INLINE int ALT_ALWAYS_INLINE alt_irq_enabled (void)
97 {
98 int status;
99
100 NIOS2_READ_STATUS (status);
101
102 return status & NIOS2_STATUS_PIE_MSK;
103 }
104
105 /*
106 * alt_irq_disable_all()
107 *
108 * This routine inhibits all interrupts by negating the status register PIE
109 * bit. It returns the previous contents of the CPU status register (IRQ
110 * context) which can be used to restore the status register PIE bit to its
111 * state before this routine was called.
112 */
113 static ALT_INLINE alt_irq_context ALT_ALWAYS_INLINE
114 alt_irq_disable_all (void)
115 {
116 alt_irq_context context;
117
118 NIOS2_READ_STATUS (context);
119
120 NIOS2_WRITE_STATUS (context & ~NIOS2_STATUS_PIE_MSK);
121
122 return context;
123 }
124
125 /*
126 * alt_irq_enable_all()
127 *
128 * Enable all interrupts that were previously disabled by alt_irq_disable_all()
129 *
130 * This routine accepts a context to restore the CPU status register PIE bit
131 * to the state prior to a call to alt_irq_disable_all().
132
133 * In the case of nested calls to alt_irq_disable_all()/alt_irq_enable_all(),
134 * this means that alt_irq_enable_all() does not necessarily re-enable
135 * interrupts.
136 *
137 * This routine will perform a read-modify-write sequence to restore only
138 * status.PIE if the processor is configured with options that add additional
139 * writeable status register bits. These include the MMU, MPU, the enhanced
140 * interrupt controller port, and shadow registers. Otherwise, as a performance
141 * enhancement, status is overwritten with the prior context.
142 */
143 static ALT_INLINE void ALT_ALWAYS_INLINE
144 alt_irq_enable_all (alt_irq_context context)
145 {
146 #if (NIOS2_NUM_OF_SHADOW_REG_SETS > 0) || (defined NIOS2_EIC_PRESENT) || \
147 (defined NIOS2_MMU_PRESENT) || (defined NIOS2_MPU_PRESENT)
148 alt_irq_context status;
149
150 NIOS2_READ_STATUS (status);
151
152 status &= ~NIOS2_STATUS_PIE_MSK;
153 status |= (context & NIOS2_STATUS_PIE_MSK);
154
155 NIOS2_WRITE_STATUS (status);
156 #else
157 NIOS2_WRITE_STATUS (context);
158 #endif
159 }
160
161 /*
162 * The function alt_irq_init() is defined within the auto-generated file
163 * alt_sys_init.c. This function calls the initilization macros for all
164 * interrupt controllers in the system at config time, before any other
165 * non-interrupt controller driver is initialized.
166 *
167 * The "base" parameter is ignored and only present for backwards-compatibility.
168 * It is recommended that NULL is passed in for the "base" parameter.
169 */
170 extern void alt_irq_init (const void* base);
171
172 /*
173 * alt_irq_cpu_enable_interrupts() enables the CPU to start taking interrupts.
174 */
175 static ALT_INLINE void ALT_ALWAYS_INLINE
176 alt_irq_cpu_enable_interrupts ()
177 {
178 NIOS2_WRITE_STATUS(NIOS2_STATUS_PIE_MSK
179 #if defined(NIOS2_EIC_PRESENT) && (NIOS2_NUM_OF_SHADOW_REG_SETS > 0)
180 | NIOS2_STATUS_RSIE_MSK
181 #endif
182 );
183 }
184
185
186 /*
187 * Prototypes for the enhanced interrupt API.
188 */
189 #ifdef ALT_ENHANCED_INTERRUPT_API_PRESENT
190 /*
191 * alt_ic_isr_register() can be used to register an interrupt handler. If the
192 * function is succesful, then the requested interrupt will be enabled upon
193 * return.
194 */
195 extern int alt_ic_isr_register(alt_u32 ic_id,
196 alt_u32 irq,
197 alt_isr_func isr,
198 void *isr_context,
199 void *flags);
200
201 /*
202 * alt_ic_irq_enable() and alt_ic_irq_disable() enable/disable a specific
203 * interrupt by using IRQ port and interrupt controller instance.
204 */
205 int alt_ic_irq_enable (alt_u32 ic_id, alt_u32 irq);
206 int alt_ic_irq_disable(alt_u32 ic_id, alt_u32 irq);
207
208 /*
209 * alt_ic_irq_enabled() indicates whether a specific interrupt, as
210 * specified by IRQ port and interrupt controller instance is enabled.
211 */
212 alt_u32 alt_ic_irq_enabled(alt_u32 ic_id, alt_u32 irq);
213
214 #else
215 /*
216 * Prototypes for the legacy interrupt API.
217 */
218 #include "priv/alt_legacy_irq.h"
219 #endif
220
221
222 /*
223 * alt_irq_pending() returns a bit list of the current pending interrupts.
224 * This is used by alt_irq_handler() to determine which registered interrupt
225 * handlers should be called.
226 *
227 * This routine is only available for the Nios II internal interrupt
228 * controller.
229 */
230 #ifndef NIOS2_EIC_PRESENT
231 static ALT_INLINE alt_u32 ALT_ALWAYS_INLINE alt_irq_pending (void)
232 {
233 alt_u32 active;
234
235 NIOS2_READ_IPENDING (active);
236
237 return active;
238 }
239 #endif
240
241 #ifdef __cplusplus
242 }
243 #endif /* __cplusplus */
244
245 #endif /* __ALT_IRQ_H__ */

186行

1 /*
2 * Prototypes for the enhanced interrupt API.
3 */
4 #ifdef ALT_ENHANCED_INTERRUPT_API_PRESENT
5 /*
6 * alt_ic_isr_register() can be used to register an interrupt handler. If the
7 * function is succesful, then the requested interrupt will be enabled upon
8 * return.
9 */
10 extern int alt_ic_isr_register(alt_u32 ic_id,
11 alt_u32 irq,
12 alt_isr_func isr,
13 void *isr_context,
14 void *flags);
15
16 /*
17 * alt_ic_irq_enable() and alt_ic_irq_disable() enable/disable a specific
18 * interrupt by using IRQ port and interrupt controller instance.
19 */
20 int alt_ic_irq_enable (alt_u32 ic_id, alt_u32 irq);
21 int alt_ic_irq_disable(alt_u32 ic_id, alt_u32 irq);
22
23 /*
24 * alt_ic_irq_enabled() indicates whether a specific interrupt, as
25 * specified by IRQ port and interrupt controller instance is enabled.
26 */
27 alt_u32 alt_ic_irq_enabled(alt_u32 ic_id, alt_u32 irq);
28
29 #else
30 /*
31 * Prototypes for the legacy interrupt API.
32 */
33 #include "priv/alt_legacy_irq.h"
34 #endif

我们可以发现，当system.h有定义ALT_ENHANCED_INTERRUPT_API_PRESENT常数时，就有alt_ic_isr_register()可用，若没定义，则#inlclude priv/alt_legacy_irq.h。

alt_legacy_irq.h / C

1 #ifndef __ALT_LEGACY_IRQ_H__
2 #define __ALT_LEGACY_IRQ_H__
3
4 /******************************************************************************
5 * *
6 * License Agreement *
7 * *
8 * Copyright (c) 2009 Altera Corporation, San Jose, California, USA. *
9 * All rights reserved. *
10 * *
11 * Permission is hereby granted, free of charge, to any person obtaining a *
12 * copy of this software and associated documentation files (the "Software"), *
13 * to deal in the Software without restriction, including without limitation *
14 * the rights to use, copy, modify, merge, publish, distribute, sublicense, *
15 * and/or sell copies of the Software, and to permit persons to whom the *
16 * Software is furnished to do so, subject to the following conditions: *
17 * *
18 * The above copyright notice and this permission notice shall be included in *
19 * all copies or substantial portions of the Software. *
20 * *
21 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR *
22 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, *
23 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE *
24 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER *
25 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING *
26 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER *
27 * DEALINGS IN THE SOFTWARE. *
28 * *
29 * This agreement shall be governed in all respects by the laws of the State *
30 * of California and by the laws of the United States of America. *
31 * *
32 ******************************************************************************/
33
34 /*
35 * This file provides prototypes and inline implementations of certain routines
36 * used by the legacy interrupt API. Do not include this in your driver or
37 * application source files, use "sys/alt_irq.h" instead to access the proper
38 * public API.
39 */
40
41 #include <errno.h>
42 #include "system.h"
43
44 #ifndef NIOS2_EIC_PRESENT
45
46 #include "nios2.h"
47 #include "alt_types.h"
48
49 #include "sys/alt_irq.h"
50
51 #ifdef __cplusplus
52 extern "C"
53 {
54 #endif /* __cplusplus */
55
56 /*
57 * alt_irq_register() can be used to register an interrupt handler. If the
58 * function is succesful, then the requested interrupt will be enabled upon
59 * return.
60 */
61 extern int alt_irq_register (alt_u32 id,
62 void* context,
63 alt_isr_func handler);
64
65 /*
66 * alt_irq_disable() disables the individual interrupt indicated by "id".
67 */
68 static ALT_INLINE int ALT_ALWAYS_INLINE alt_irq_disable (alt_u32 id)
69 {
70 alt_irq_context status;
71 extern volatile alt_u32 alt_irq_active;
72
73 status = alt_irq_disable_all ();
74
75 alt_irq_active &= ~(1 << id);
76 NIOS2_WRITE_IENABLE (alt_irq_active);
77
78 alt_irq_enable_all(status);
79
80 return 0;
81 }
82
83 /*
84 * alt_irq_enable() enables the individual interrupt indicated by "id".
85 */
86 static ALT_INLINE int ALT_ALWAYS_INLINE alt_irq_enable (alt_u32 id)
87 {
88 alt_irq_context status;
89 extern volatile alt_u32 alt_irq_active;
90
91 status = alt_irq_disable_all ();
92
93 alt_irq_active |= (1 << id);
94 NIOS2_WRITE_IENABLE (alt_irq_active);
95
96 alt_irq_enable_all(status);
97
98 return 0;
99 }
100
101 #ifndef ALT_EXCEPTION_STACK
102 /*
103 * alt_irq_initerruptable() should only be called from within an ISR. It is used
104 * to allow higer priority interrupts to interrupt the current ISR. The input
105 * argument, "priority", is the priority, i.e. interrupt number of the current
106 * interrupt.
107 *
108 * If this function is called, then the ISR is required to make a call to
109 * alt_irq_non_interruptible() before returning. The input argument to
110 * alt_irq_non_interruptible() is the return value from alt_irq_interruptible().
111 *
112 * Care should be taken when using this pair of functions, since they increasing
113 * the system overhead associated with interrupt handling.
114 *
115 * If you are using an exception stack then nested interrupts won't work, so
116 * these functions are not available in that case.
117 */
118 static ALT_INLINE alt_u32 ALT_ALWAYS_INLINE alt_irq_interruptible (alt_u32 priority)
119 {
120 extern volatile alt_u32 alt_priority_mask;
121 extern volatile alt_u32 alt_irq_active;
122
123 alt_u32 old_priority;
124
125 old_priority = alt_priority_mask;
126 alt_priority_mask = (1 << priority) - 1;
127
128 NIOS2_WRITE_IENABLE (alt_irq_active & alt_priority_mask);
129
130 NIOS2_WRITE_STATUS (1);
131
132 return old_priority;
133 }
134
135 /*
136 * See Comments above for alt_irq_interruptible() for an explanation of the use of this
137 * function.
138 */
139 static ALT_INLINE void ALT_ALWAYS_INLINE alt_irq_non_interruptible (alt_u32 mask)
140 {
141 extern volatile alt_u32 alt_priority_mask;
142 extern volatile alt_u32 alt_irq_active;
143
144 NIOS2_WRITE_STATUS (0);
145
146 alt_priority_mask = mask;
147
148 NIOS2_WRITE_IENABLE (mask & alt_irq_active);
149 }
150 #endif /* ALT_EXCEPTION_STACK */
151
152 #ifdef __cplusplus
153 }
154 #endif /* __cplusplus */
155
156 #endif /* NIOS2_EIC_PRESENT */
157
158 #endif /* __ALT_LEGACY_IRQ_H__ */

61行

extern int alt_irq_register (alt_u32 id,
void* context,
alt_isr_func handler);

则是我们所用旧的alt_irq_register()。

至于ISR的prototype新旧不一样，trace的方式也一样，就不再赘述。

至于为什么目前在subsystem的interrupt只能使用旧的ISR register方式，我并不清楚，或许Quartus II未来版本会有所改变。

使用以上方法后，就可正确的在App project收到subsystem的interrupt了。

Conclusion
我们在本文看到了Qsys与SOPC Builder在subsystem与interrupt的处理有很大的差异，也看到了目前Qsys与Nios II SBT尚有些bug待修正。目前Quartus II 11.0与Quartus II 11.1都还有system.h的bug，相信未来的版本一定会修正这个问题。假如你现在要在subsystem使用interrupt，可暂时使用本文的方式当作short term solution。

Reference
[1] Qsys Interconnect
[2] Quartus II 11.0 Release Notes
[3] Altera Wiki : New Qsys Issues for Interrupts
[4] Exception Handling

全文完。