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>eCos Reference Manual</TH
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><H1
81 
><A
82 
NAME="KERNEL-INTERRUPTS">Interrupt Handling</H1
83 
><DIV
84 
CLASS="REFNAMEDIV"
85 
><A
86 
NAME="AEN1834"
87 
></A
88 
><H2
89 
>Name</H2
90 
>cyg_interrupt_create, cyg_interrupt_delete, cyg_interrupt_attach, cyg_interrupt_detach, cyg_interrupt_configure, cyg_interrupt_acknowledge, cyg_interrupt_enable, cyg_interrupt_disable, cyg_interrupt_mask, cyg_interrupt_mask_intunsafe, cyg_interrupt_unmask, cyg_interrupt_unmask_intunsafe, cyg_interrupt_set_cpu, cyg_interrupt_get_cpu, cyg_interrupt_get_vsr, cyg_interrupt_set_vsr&nbsp;--&nbsp;Manage interrupt handlers</DIV
91 
><DIV
92 
CLASS="REFSYNOPSISDIV"
93 
><A
94 
NAME="AEN1852"><H2
95 
>Synopsis</H2
96 
><DIV
97 
CLASS="FUNCSYNOPSIS"
98 
><A
99 
NAME="AEN1853"><P
100 
></P
101 
><TABLE
102 
BORDER="5"
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BGCOLOR="#E0E0F0"
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WIDTH="70%"
105 
><TR
106 
><TD
107 
><PRE
108 
CLASS="FUNCSYNOPSISINFO"
109 
>#include &lt;cyg/kernel/kapi.h&gt;
110 
        </PRE
111 
></TD
112 
></TR
113 
></TABLE
114 
><P
115 
><CODE
116 
><CODE
117 
CLASS="FUNCDEF"
118 
>void cyg_interrupt_create</CODE
119 
>(cyg_vector_t vector, cyg_priority_t priority, cyg_addrword_t data, cyg_ISR_t* isr, cyg_DSR_t* dsr, cyg_handle_t* handle, cyg_interrupt* intr);</CODE
120 
></P
121 
><P
122 
><CODE
123 
><CODE
124 
CLASS="FUNCDEF"
125 
>void cyg_interrupt_delete</CODE
126 
>(cyg_handle_t interrupt);</CODE
127 
></P
128 
><P
129 
><CODE
130 
><CODE
131 
CLASS="FUNCDEF"
132 
>void cyg_interrupt_attach</CODE
133 
>(cyg_handle_t interrupt);</CODE
134 
></P
135 
><P
136 
><CODE
137 
><CODE
138 
CLASS="FUNCDEF"
139 
>void cyg_interrupt_detach</CODE
140 
>(cyg_handle_t interrupt);</CODE
141 
></P
142 
><P
143 
><CODE
144 
><CODE
145 
CLASS="FUNCDEF"
146 
>void cyg_interrupt_configure</CODE
147 
>(cyg_vector_t vector, cyg_bool_t level, cyg_bool_t up);</CODE
148 
></P
149 
><P
150 
><CODE
151 
><CODE
152 
CLASS="FUNCDEF"
153 
>void cyg_interrupt_acknowledge</CODE
154 
>(cyg_vector_t vector);</CODE
155 
></P
156 
><P
157 
><CODE
158 
><CODE
159 
CLASS="FUNCDEF"
160 
>void cyg_interrupt_disable</CODE
161 
>(void);</CODE
162 
></P
163 
><P
164 
><CODE
165 
><CODE
166 
CLASS="FUNCDEF"
167 
>void cyg_interrupt_enable</CODE
168 
>(void);</CODE
169 
></P
170 
><P
171 
><CODE
172 
><CODE
173 
CLASS="FUNCDEF"
174 
>void cyg_interrupt_mask</CODE
175 
>(cyg_vector_t vector);</CODE
176 
></P
177 
><P
178 
><CODE
179 
><CODE
180 
CLASS="FUNCDEF"
181 
>void cyg_interrupt_mask_intunsafe</CODE
182 
>(cyg_vector_t vector);</CODE
183 
></P
184 
><P
185 
><CODE
186 
><CODE
187 
CLASS="FUNCDEF"
188 
>void cyg_interrupt_unmask</CODE
189 
>(cyg_vector_t vector);</CODE
190 
></P
191 
><P
192 
><CODE
193 
><CODE
194 
CLASS="FUNCDEF"
195 
>void cyg_interrupt_unmask_intunsafe</CODE
196 
>(cyg_vector_t vector);</CODE
197 
></P
198 
><P
199 
><CODE
200 
><CODE
201 
CLASS="FUNCDEF"
202 
>void cyg_interrupt_set_cpu</CODE
203 
>(cyg_vector_t vector, cyg_cpu_t cpu);</CODE
204 
></P
205 
><P
206 
><CODE
207 
><CODE
208 
CLASS="FUNCDEF"
209 
>cyg_cpu_t cyg_interrupt_get_cpu</CODE
210 
>(cyg_vector_t vector);</CODE
211 
></P
212 
><P
213 
><CODE
214 
><CODE
215 
CLASS="FUNCDEF"
216 
>void cyg_interrupt_get_vsr</CODE
217 
>(cyg_vector_t vector, cyg_VSR_t** vsr);</CODE
218 
></P
219 
><P
220 
><CODE
221 
><CODE
222 
CLASS="FUNCDEF"
223 
>void cyg_interrupt_set_vsr</CODE
224 
>(cyg_vector_t vector, cyg_VSR_t* vsr);</CODE
225 
></P
226 
><P
227 
></P
228 
></DIV
229 
></DIV
230 
><DIV
231 
CLASS="REFSECT1"
232 
><A
233 
NAME="KERNEL-INTERRUPTS-DESCRIPTION"
234 
></A
235 
><H2
236 
>Description</H2
237 
><P
238 
>The kernel provides an interface for installing interrupt handlers and
239 
controlling when interrupts occur. This functionality is used
240 
primarily by eCos device drivers and by any application code that
241 
interacts directly with hardware. However in most cases it is better
242 
to avoid using this kernel functionality directly, and instead the
243 
device driver API provided by the common HAL package should be used.
244 
Use of the kernel package is optional, and some applications such as
245 
RedBoot work with no need for multiple threads or synchronization
246 
primitives. Any code which calls the kernel directly rather than the
247 
device driver API will not function in such a configuration. When the
248 
kernel package is present the device driver API is implemented as
249 
<TT
250 
CLASS="LITERAL"
251 
>#define</TT
252 
>'s to the equivalent kernel calls, otherwise
253 
it is implemented inside the common HAL package. The latter
254 
implementation can be simpler than the kernel one because there is no
255 
need to consider thread preemption and similar issues.
256 
      </P
257 
><P
258 
>The exact details of interrupt handling vary widely between
259 
architectures. The functionality provided by the kernel abstracts away
260 
from many of the details of the underlying hardware, thus simplifying
261 
application development. However this is not always successful. For
262 
example, if some hardware does not provide any support at all for
263 
masking specific interrupts then calling
264 
<TT
265 
CLASS="FUNCTION"
266 
>cyg_interrupt_mask</TT
267 
> may not behave as intended:
268 
instead of masking just the one interrupt source it might disable all
269 
interrupts, because that is as close to the desired behaviour as is
270 
possible given the hardware restrictions. Another possibility is that
271 
masking a given interrupt source also affects all lower-priority
272 
interrupts, but still allows higher-priority ones. The documentation
273 
for the appropriate HAL packages should be consulted for more
274 
information about exactly how interrupts are handled on any given
275 
hardware. The HAL header files will also contain useful information.
276 
      </P
277 
></DIV
278 
><DIV
279 
CLASS="REFSECT1"
280 
><A
281 
NAME="KERNEL-INTERRUPTS-HANDLERS"
282 
></A
283 
><H2
284 
>Interrupt Handlers</H2
285 
><P
286 
>Interrupt handlers are created by a call to
287 
<TT
288 
CLASS="FUNCTION"
289 
>cyg_interrupt_create</TT
290 
>. This takes the following
291 
arguments:
292 
      </P
293 
><P
294 
></P
295 
><DIV
296 
CLASS="VARIABLELIST"
297 
><DL
298 
><DT
299 
>cyg_vector_t <TT
300 
CLASS="PARAMETER"
301 
><I
302 
>vector</I
303 
></TT
304 
></DT
305 
><DD
306 
><P
307 
>The interrupt vector, a small integer, identifies the specific
308 
interrupt source. The appropriate hardware documentation or HAL header
309 
files should be consulted for details of which vector corresponds to
310 
which device.
311 
          </P
312 
></DD
313 
><DT
314 
>cyg_priority_t <TT
315 
CLASS="PARAMETER"
316 
><I
317 
>priority</I
318 
></TT
319 
></DT
320 
><DD
321 
><P
322 
>Some hardware may support interrupt priorities, where a low priority
323 
interrupt handler can in turn be interrupted by a higher priority one.
324 
Again hardware-specific documentation should be consulted for details
325 
about what the valid interrupt priority levels are.
326 
          </P
327 
></DD
328 
><DT
329 
>cyg_addrword_t <TT
330 
CLASS="PARAMETER"
331 
><I
332 
>data</I
333 
></TT
334 
></DT
335 
><DD
336 
><P
337 
>When an interrupt occurs eCos will first call the associated
338 
interrupt service routine or ISR, then optionally a deferred service
339 
routine or DSR. The <TT
340 
CLASS="PARAMETER"
341 
><I
342 
>data</I
343 
></TT
344 
> argument to
345 
<TT
346 
CLASS="FUNCTION"
347 
>cyg_interrupt_create</TT
348 
> will be passed to both these
349 
functions. Typically it will be a pointer to some data structure.
350 
          </P
351 
></DD
352 
><DT
353 
>cyg_ISR_t <TT
354 
CLASS="PARAMETER"
355 
><I
356 
>isr</I
357 
></TT
358 
></DT
359 
><DD
360 
><P
361 
>When an interrupt occurs the hardware will transfer control to the
362 
appropriate vector service routine or VSR, which is usually provided
363 
by eCos. This performs any appropriate processing, for example to work
364 
out exactly which interrupt occurred, and then as quickly as possible
365 
transfers control the installed ISR. An ISR is a C function which
366 
takes the following form:
367 
          </P
368 
><TABLE
369 
BORDER="5"
370 
BGCOLOR="#E0E0F0"
371 
WIDTH="70%"
372 
><TR
373 
><TD
374 
><PRE
375 
CLASS="PROGRAMLISTING"
376 
>cyg_uint32
377 
isr_function(cyg_vector_t vector, cyg_addrword_t data)
378 
{
379 
    cyg_bool_t dsr_required = 0;
380 
 
381 
    &#8230;
382 
 
383 
    return dsr_required ? CYG_ISR_CALL_DSR : CYG_ISR_HANDLED;
384 
}
385 
          </PRE
386 
></TD
387 
></TR
388 
></TABLE
389 
><P
390 
>The first argument identifies the particular interrupt source,
391 
especially useful if there multiple instances of a given device and a
392 
single ISR can be used for several different interrupt vectors. The
393 
second argument is the <TT
394 
CLASS="PARAMETER"
395 
><I
396 
>data</I
397 
></TT
398 
> field passed to
399 
<TT
400 
CLASS="FUNCTION"
401 
>cyg_interrupt_create</TT
402 
>, usually a pointer to some
403 
data structure. The exact conditions under which an ISR runs will
404 
depend partly on the hardware and partly on configuration options.
405 
Interrupts may currently be disabled globally, especially if the
406 
hardware does not support interrupt priorities. Alternatively
407 
interrupts may be enabled such that higher priority interrupts are
408 
allowed through. The ISR may be running on a separate interrupt stack,
409 
or on the stack of whichever thread was running at the time the
410 
interrupt happened.
411 
          </P
412 
><P
413 
>A typical ISR will do as little work as possible, just enough to meet
414 
the needs of the hardware and then acknowledge the interrupt by
415 
calling <TT
416 
CLASS="FUNCTION"
417 
>cyg_interrupt_acknowledge</TT
418 
>. This ensures
419 
that interrupts will be quickly reenabled, so higher priority devices
420 
can be serviced. For some applications there may be one device which
421 
is especially important and whose ISR can take much longer than
422 
normal. However eCos device drivers usually will not assume that they
423 
are especially important, so their ISRs will be as short as possible.
424 
          </P
425 
><P
426 
>The return value of an ISR is normally one of
427 
<TT
428 
CLASS="LITERAL"
429 
>CYG_ISR_CALL_DSR</TT
430 
> or
431 
<TT
432 
CLASS="LITERAL"
433 
>CYG_ISR_HANDLED</TT
434 
>. The former indicates that further
435 
processing is required at DSR level, and the interrupt handler's DSR
436 
will be run as soon as possible. The latter indicates that the
437 
interrupt has been fully handled and no further effort is required.
438 
          </P
439 
><P
440 
>An ISR is allowed to make very few kernel calls. It can manipulate the
441 
interrupt mask, and on SMP systems it can use spinlocks. However an
442 
ISR must not make higher-level kernel calls such as posting to a
443 
semaphore, instead any such calls must be made from the DSR. This
444 
avoids having to disable interrupts throughout the kernel and thus
445 
improves interrupt latency.
446 
          </P
447 
></DD
448 
><DT
449 
>cyg_DSR_t <TT
450 
CLASS="PARAMETER"
451 
><I
452 
>dsr</I
453 
></TT
454 
></DT
455 
><DD
456 
><P
457 
>If an interrupt has occurred and the ISR has returned a value
458 
<TT
459 
CLASS="LITERAL"
460 
>CYG_ISR_CALL_DSR</TT
461 
>, the system will call the
462 
deferred service routine or DSR associated with this interrupt
463 
handler. If the scheduler is not currently locked then the DSR will
464 
run immediately. However if the interrupted thread was in the middle
465 
of a kernel call and had locked the scheduler, then the DSR will be
466 
deferred until the scheduler is again unlocked. This allows the
467 
DSR to make certain kernel calls safely, for example posting to a
468 
semaphore or signalling a condition variable. A DSR is a C function
469 
which takes the following form:
470 
          </P
471 
><TABLE
472 
BORDER="5"
473 
BGCOLOR="#E0E0F0"
474 
WIDTH="70%"
475 
><TR
476 
><TD
477 
><PRE
478 
CLASS="PROGRAMLISTING"
479 
>void
480 
dsr_function(cyg_vector_t vector,
481 
             cyg_ucount32 count,
482 
             cyg_addrword_t data)
483 
{
484 
}
485 
          </PRE
486 
></TD
487 
></TR
488 
></TABLE
489 
><P
490 
>The first argument identifies the specific interrupt that has caused
491 
the DSR to run. The second argument indicates the number of these
492 
interrupts that have occurred and for which the ISR requested a DSR.
493 
Usually this will be <TT
494 
CLASS="LITERAL"
495 
>1</TT
496 
>, unless the system is
497 
suffering from a very heavy load. The third argument is the
498 
<TT
499 
CLASS="PARAMETER"
500 
><I
501 
>data</I
502 
></TT
503 
> field passed to
504 
<TT
505 
CLASS="FUNCTION"
506 
>cyg_interrupt_create</TT
507 
>.
508 
          </P
509 
></DD
510 
><DT
511 
>cyg_handle_t* <TT
512 
CLASS="PARAMETER"
513 
><I
514 
>handle</I
515 
></TT
516 
></DT
517 
><DD
518 
><P
519 
>The kernel will return a handle to the newly created interrupt handler
520 
via this argument. Subsequent operations on the interrupt handler such
521 
as attaching it to the interrupt source will use this handle.
522 
          </P
523 
></DD
524 
><DT
525 
>cyg_interrupt* <TT
526 
CLASS="PARAMETER"
527 
><I
528 
>intr</I
529 
></TT
530 
></DT
531 
><DD
532 
><P
533 
>This provides the kernel with an area of memory for holding this
534 
interrupt handler and associated data.
535 
          </P
536 
></DD
537 
></DL
538 
></DIV
539 
><P
540 
>The call to <TT
541 
CLASS="FUNCTION"
542 
>cyg_interrupt_create</TT
543 
> simply fills in
544 
a kernel data structure. A typical next step is to call
545 
<TT
546 
CLASS="FUNCTION"
547 
>cyg_interrupt_attach</TT
548 
> using the handle returned by
549 
the create operation. This makes it possible to have several different
550 
interrupt handlers for a given vector, attaching whichever one is
551 
currently appropriate. Replacing an interrupt handler requires a call
552 
to <TT
553 
CLASS="FUNCTION"
554 
>cyg_interrupt_detach</TT
555 
>, followed by another call
556 
to <TT
557 
CLASS="FUNCTION"
558 
>cyg_interrupt_attach</TT
559 
> for the replacement
560 
handler. <TT
561 
CLASS="FUNCTION"
562 
>cyg_interrupt_delete</TT
563 
> can be used if an
564 
interrupt handler is no longer required.
565 
      </P
566 
><P
567 
>Some hardware may allow for further control over specific interrupts,
568 
for example whether an interrupt is level or edge triggered. Any such
569 
hardware functionality can be accessed using
570 
<TT
571 
CLASS="FUNCTION"
572 
>cyg_interrupt_configure</TT
573 
>: the
574 
<TT
575 
CLASS="PARAMETER"
576 
><I
577 
>level</I
578 
></TT
579 
> argument selects between level versus
580 
edge triggered; the <TT
581 
CLASS="PARAMETER"
582 
><I
583 
>up</I
584 
></TT
585 
> argument selects between
586 
high and low level, or between rising and falling edges.
587 
      </P
588 
><P
589 
>Usually interrupt handlers are created, attached and configured during
590 
system initialization, while global interrupts are still disabled. On
591 
most hardware it will also be necessary to call
592 
<TT
593 
CLASS="FUNCTION"
594 
>cyg_interrupt_unmask</TT
595 
>, since the sensible default
596 
for interrupt masking is to ignore any interrupts for which no handler
597 
is installed.
598 
      </P
599 
></DIV
600 
><DIV
601 
CLASS="REFSECT1"
602 
><A
603 
NAME="KERNEL-INTERRUPTS-ENABLE"
604 
></A
605 
><H2
606 
>Controlling Interrupts</H2
607 
><P
608 
>eCos provides two ways of controlling whether or not interrupts
609 
happen. It is possible to disable and reenable all interrupts
610 
globally, using <TT
611 
CLASS="FUNCTION"
612 
>cyg_interrupt_disable</TT
613 
> and
614 
<TT
615 
CLASS="FUNCTION"
616 
>cyg_interrupt_enable</TT
617 
>. Typically this works by
618 
manipulating state inside the cpu itself, for example setting a flag
619 
in a status register or executing special instructions. Alternatively
620 
it may be possible to mask a specific interrupt source by writing to
621 
one or to several interrupt mask registers. Hardware-specific
622 
documentation should be consulted for the exact details of how
623 
interrupt masking works, because a full implementation is not possible
624 
on all hardware.
625 
      </P
626 
><P
627 
>The primary use for these functions is to allow data to be shared
628 
between ISRs and other code such as DSRs or threads. If both a thread
629 
and an ISR need to manipulate either a data structure or the hardware
630 
itself, there is a possible conflict if an interrupt happens just when
631 
the thread is doing such manipulation. Problems can be avoided by the
632 
thread either disabling or masking interrupts during the critical
633 
region. If this critical region requires only a few instructions then
634 
usually it is more efficient to disable interrupts. For larger
635 
critical regions it may be more appropriate to use interrupt masking,
636 
allowing other interrupts to occur. There are other uses for interrupt
637 
masking. For example if a device is not currently being used by the
638 
application then it may be desirable to mask all interrupts generated
639 
by that device.
640 
      </P
641 
><P
642 
>There are two functions for masking a specific interrupt source,
643 
<TT
644 
CLASS="FUNCTION"
645 
>cyg_interrupt_mask</TT
646 
> and
647 
<TT
648 
CLASS="FUNCTION"
649 
>cyg_interrupt_mask_intunsafe</TT
650 
>. On typical hardware
651 
masking an interrupt is not an atomic operation, so if two threads
652 
were to perform interrupt masking operations at the same time there
653 
could be problems. <TT
654 
CLASS="FUNCTION"
655 
>cyg_interrupt_mask</TT
656 
> disables
657 
all interrupts while it manipulates the interrupt mask. In situations
658 
where interrupts are already know to be disabled,
659 
<TT
660 
CLASS="FUNCTION"
661 
>cyg_interrupt_mask_intunsafe</TT
662 
> can be used
663 
instead. There are matching functions
664 
<TT
665 
CLASS="FUNCTION"
666 
>cyg_interrupt_unmask</TT
667 
> and
668 
<TT
669 
CLASS="FUNCTION"
670 
>cyg_interrupt_unmask_intsafe</TT
671 
>.
672 
      </P
673 
></DIV
674 
><DIV
675 
CLASS="REFSECT1"
676 
><A
677 
NAME="KERNEL-INTERRUPTS-SMP"
678 
></A
679 
><H2
680 
>SMP Support</H2
681 
><P
682 
>On SMP systems the kernel provides an additional two functions related
683 
to interrupt handling. <TT
684 
CLASS="FUNCTION"
685 
>cyg_interrupt_set_cpu</TT
686 
>
687 
specifies that a particular hardware interrupt should always be
688 
handled on one specific processor in the system. In other words when
689 
the interrupt triggers it is only that processor which detects it, and
690 
it is only on that processor that the VSR and ISR will run. If a DSR
691 
is requested then it will also run on the same CPU. The
692 
function <TT
693 
CLASS="FUNCTION"
694 
>cyg_interrupt_get_cpu</TT
695 
> can be used to
696 
find out which interrupts are handled on which processor.
697 
      </P
698 
></DIV
699 
><DIV
700 
CLASS="REFSECT1"
701 
><A
702 
NAME="KERNEL-INTERRUPTS-VSR"
703 
></A
704 
><H2
705 
>VSR Support</H2
706 
><P
707 
>When an interrupt occurs the hardware will transfer control to a piece
708 
of code known as the VSR, or Vector Service Routine. By default this
709 
code is provided by eCos. Usually it is written in assembler, but on
710 
some architectures it may be possible to implement VSRs in C by
711 
specifying an interrupt attribute. Compiler documentation should be
712 
consulted for more information on this. The default eCos VSR will work
713 
out which ISR function should process the interrupt, and set up a C
714 
environment suitable for this ISR.
715 
      </P
716 
><P
717 
>For some applications it may be desirable to replace the default eCos
718 
VSR and handle some interrupts directly. This minimizes interrupt
719 
latency, but it requires application developers to program at a lower
720 
level. Usually the best way to write a custom VSR is to copy the
721 
existing one supplied by eCos and then make appropriate modifications.
722 
The function <TT
723 
CLASS="FUNCTION"
724 
>cyg_interrupt_get_vsr</TT
725 
> can be used to
726 
get hold of the current VSR for a given interrupt vector, allowing it
727 
to be restored if the custom VSR is no longer required.
728 
<TT
729 
CLASS="FUNCTION"
730 
>cyg_interrupt_set_vsr</TT
731 
> can be used to install a
732 
replacement VSR. Usually the <TT
733 
CLASS="PARAMETER"
734 
><I
735 
>vsr</I
736 
></TT
737 
> argument will
738 
correspond to an exported label in an assembler source file.
739 
      </P
740 
></DIV
741 
><DIV
742 
CLASS="REFSECT1"
743 
><A
744 
NAME="KERNEL-INTERRUPTS-CONTEXT"
745 
></A
746 
><H2
747 
>Valid contexts</H2
748 
><P
749 
>In a typical configuration interrupt handlers are created and attached
750 
during system initialization, and never detached or deleted. However
751 
it is possible to perform these operations at thread level, if
752 
desired. Similarly <TT
753 
CLASS="FUNCTION"
754 
>cyg_interrupt_configure</TT
755 
>,
756 
<TT
757 
CLASS="FUNCTION"
758 
>cyg_interrupt_set_vsr</TT
759 
>, and
760 
<TT
761 
CLASS="FUNCTION"
762 
>cyg_interrupt_set_cpu</TT
763 
> are usually called only
764 
during system initialization, but on typical hardware may be called at
765 
any time. <TT
766 
CLASS="FUNCTION"
767 
>cyg_interrupt_get_vsr</TT
768 
> and
769 
<TT
770 
CLASS="FUNCTION"
771 
>cyg_interrupt_get_cpu</TT
772 
> may be called at any time.
773 
      </P
774 
><P
775 
>The functions for enabling, disabling, masking and unmasking
776 
interrupts can be called in any context, when appropriate. It is the
777 
responsibility of application developers to determine when the use of
778 
these functions is appropriate.
779 
      </P
780 
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