OpenCores
URL https://opencores.org/ocsvn/openrisc/openrisc/trunk

Subversion Repositories openrisc

[/] [openrisc/] [trunk/] [rtos/] [ecos-2.0/] [doc/] [html/] [ref/] [kernel-exceptions.html] - Blame information for rev 765

Go to most recent revision | Details | Compare with Previous | View Log

Line No. Rev Author Line
1 28 unneback 
<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
2 
<!-- This material may be distributed only subject to the terms      -->
3 
<!-- and conditions set forth in the Open Publication License, v1.0  -->
4 
<!-- or later (the latest version is presently available at          -->
5 
<!-- http://www.opencontent.org/openpub/).                           -->
6 
<!-- Distribution of the work or derivative of the work in any       -->
7 
<!-- standard (paper) book form is prohibited unless prior           -->
8 
<!-- permission is obtained from the copyright holder.               -->
9 
<HTML
10 
><HEAD
11 
><TITLE
12 
>Exception handling</TITLE
13 
><meta name="MSSmartTagsPreventParsing" content="TRUE">
14 
<META
15 
NAME="GENERATOR"
16 
CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+
17 
"><LINK
18 
REL="HOME"
19 
TITLE="eCos Reference Manual"
20 
HREF="ecos-ref.html"><LINK
21 
REL="UP"
22 
TITLE="The eCos Kernel"
23 
HREF="kernel.html"><LINK
24 
REL="PREVIOUS"
25 
TITLE="Thread destructors"
26 
HREF="kernel-thread-destructors.html"><LINK
27 
REL="NEXT"
28 
TITLE="Counters"
29 
HREF="kernel-counters.html"></HEAD
30 
><BODY
31 
CLASS="REFENTRY"
32 
BGCOLOR="#FFFFFF"
33 
TEXT="#000000"
34 
LINK="#0000FF"
35 
VLINK="#840084"
36 
ALINK="#0000FF"
37 
><DIV
38 
CLASS="NAVHEADER"
39 
><TABLE
40 
SUMMARY="Header navigation table"
41 
WIDTH="100%"
42 
BORDER="0"
43 
CELLPADDING="0"
44 
CELLSPACING="0"
45 
><TR
46 
><TH
47 
COLSPAN="3"
48 
ALIGN="center"
49 
>eCos Reference Manual</TH
50 
></TR
51 
><TR
52 
><TD
53 
WIDTH="10%"
54 
ALIGN="left"
55 
VALIGN="bottom"
56 
><A
57 
HREF="kernel-thread-destructors.html"
58 
ACCESSKEY="P"
59 
>Prev</A
60 
></TD
61 
><TD
62 
WIDTH="80%"
63 
ALIGN="center"
64 
VALIGN="bottom"
65 
></TD
66 
><TD
67 
WIDTH="10%"
68 
ALIGN="right"
69 
VALIGN="bottom"
70 
><A
71 
HREF="kernel-counters.html"
72 
ACCESSKEY="N"
73 
>Next</A
74 
></TD
75 
></TR
76 
></TABLE
77 
><HR
78 
ALIGN="LEFT"
79 
WIDTH="100%"></DIV
80 
><H1
81 
><A
82 
NAME="KERNEL-EXCEPTIONS">Exception handling</H1
83 
><DIV
84 
CLASS="REFNAMEDIV"
85 
><A
86 
NAME="AEN782"
87 
></A
88 
><H2
89 
>Name</H2
90 
>cyg_exception_set_handler, cyg_exception_clear_handler, cyg_exception_call_handler&nbsp;--&nbsp;Handle processor exceptions</DIV
91 
><DIV
92 
CLASS="REFSYNOPSISDIV"
93 
><A
94 
NAME="AEN787"><H2
95 
>Synopsis</H2
96 
><DIV
97 
CLASS="FUNCSYNOPSIS"
98 
><A
99 
NAME="AEN788"><P
100 
></P
101 
><TABLE
102 
BORDER="5"
103 
BGCOLOR="#E0E0F0"
104 
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_exception_set_handler</CODE
119 
>(cyg_code_t exception_number, cyg_exception_handler_t* new_handler, cyg_addrword_t new_data, cyg_exception_handler_t** old_handler, cyg_addrword_t* old_data);</CODE
120 
></P
121 
><P
122 
><CODE
123 
><CODE
124 
CLASS="FUNCDEF"
125 
>void cyg_exception_clear_handler</CODE
126 
>(cyg_code_t exception_number);</CODE
127 
></P
128 
><P
129 
><CODE
130 
><CODE
131 
CLASS="FUNCDEF"
132 
>void cyg_exception_call_handler</CODE
133 
>(cyg_handle_t thread, cyg_code_t exception_number, cyg_addrword_t exception_info);</CODE
134 
></P
135 
><P
136 
></P
137 
></DIV
138 
></DIV
139 
><DIV
140 
CLASS="REFSECT1"
141 
><A
142 
NAME="AEN817"
143 
></A
144 
><H2
145 
>Description</H2
146 
><P
147 
>Sometimes code attempts operations that are not legal on the current
148 
hardware, for example dividing by zero, or accessing data through a
149 
pointer that is not properly aligned. When this happens the hardware
150 
will raise an exception. This is very similar to an interrupt, but
151 
happens synchronously with code execution rather than asynchronously
152 
and hence can be tied to the thread that is currently running.
153 
      </P
154 
><P
155 
>The exceptions that can be raised depend very much on the hardware,
156 
especially the processor. The corresponding documentation should be
157 
consulted for more details. Alternatively the architectural HAL header
158 
file <TT
159 
CLASS="FILENAME"
160 
>hal_intr.h</TT
161 
>, or one of the
162 
variant or platform header files it includes, will contain appropriate
163 
definitions. The details of how to handle exceptions, including
164 
whether or not it is possible to recover from them, also depend on the
165 
hardware.
166 
      </P
167 
><P
168 
>Exception handling is optional, and can be disabled through the
169 
configuration option <TT
170 
CLASS="VARNAME"
171 
>CYGPKG_KERNEL_EXCEPTIONS</TT
172 
>. If
173 
an application has been exhaustively tested and is trusted never to
174 
raise a hardware exception then this option can be disabled and code
175 
and data sizes will be reduced somewhat. If exceptions are left
176 
enabled then the system will provide default handlers for the various
177 
exceptions, but these do nothing. Even the specific type of exception
178 
is ignored, so there is no point in attempting to decode this and
179 
distinguish between say a divide-by-zero and an unaligned access.
180 
If the application installs its own handlers and wants details of the
181 
specific exception being raised then the configuration option
182 
<TT
183 
CLASS="VARNAME"
184 
>CYGSEM_KERNEL_EXCEPTIONS_DECODE</TT
185 
> has to be enabled.
186 
      </P
187 
><P
188 
>An alternative handler can be installed using
189 
<TT
190 
CLASS="FUNCTION"
191 
>cyg_exception_set_handler</TT
192 
>. This requires a code
193 
for the exception, a function pointer for the new exception handler,
194 
and a parameter to be passed to this handler. Details of the
195 
previously installed exception handler will be returned via the
196 
remaining two arguments, allowing that handler to be reinstated, or
197 
null pointers can be used if this information is of no interest. An
198 
exception handling function should take the following form:
199 
      </P
200 
><TABLE
201 
BORDER="5"
202 
BGCOLOR="#E0E0F0"
203 
WIDTH="70%"
204 
><TR
205 
><TD
206 
><PRE
207 
CLASS="PROGRAMLISTING"
208 
>void
209 
my_exception_handler(cyg_addrword_t data, cyg_code_t exception, cyg_addrword_t info)
210 
{
211 
    &#8230;
212 
}
213 
      </PRE
214 
></TD
215 
></TR
216 
></TABLE
217 
><P
218 
>The data argument corresponds to the <TT
219 
CLASS="PARAMETER"
220 
><I
221 
>new_data</I
222 
></TT
223 
>
224 
parameter supplied to <TT
225 
CLASS="FUNCTION"
226 
>cyg_exception_set_handler</TT
227 
>.
228 
The exception code is provided as well, in case a single handler is
229 
expected to support multiple exceptions. The <TT
230 
CLASS="PARAMETER"
231 
><I
232 
>info</I
233 
></TT
234 
>
235 
argument will depend on the hardware and on the specific exception.
236 
      </P
237 
><P
238 
><TT
239 
CLASS="FUNCTION"
240 
>cyg_exception_clear_handler</TT
241 
> can be used to
242 
restore the default handler, if desired. It is also possible for
243 
software to raise an exception and cause the current handler to be
244 
invoked, but generally this is useful only for testing.
245 
      </P
246 
><P
247 
>By default the system maintains a single set of global exception
248 
handlers. However, since exceptions occur synchronously it is
249 
sometimes useful to handle them on a per-thread basis, and have a
250 
different set of handlers for each thread. This behaviour can be
251 
obtained by disabling the configuration option
252 
<TT
253 
CLASS="VARNAME"
254 
>CYGSEM_KERNEL_EXCEPTIONS_GLOBAL</TT
255 
>. If per-thread
256 
exception handlers are being used then
257 
<TT
258 
CLASS="FUNCTION"
259 
>cyg_exception_set_handler</TT
260 
> and
261 
<TT
262 
CLASS="FUNCTION"
263 
>cyg_exception_clear_handler</TT
264 
> apply to the current
265 
thread. Otherwise they apply to the global set of handlers.
266 
      </P
267 
><DIV
268 
CLASS="CAUTION"
269 
><P
270 
></P
271 
><TABLE
272 
CLASS="CAUTION"
273 
BORDER="1"
274 
WIDTH="100%"
275 
><TR
276 
><TD
277 
ALIGN="CENTER"
278 
><B
279 
>Caution</B
280 
></TD
281 
></TR
282 
><TR
283 
><TD
284 
ALIGN="LEFT"
285 
><P
286 
>In the current implementation
287 
<TT
288 
CLASS="FUNCTION"
289 
>cyg_exception_call_handler</TT
290 
> can only be used on
291 
the current thread. There is no support for delivering an exception to
292 
another thread.
293 
      </P
294 
></TD
295 
></TR
296 
></TABLE
297 
></DIV
298 
><DIV
299 
CLASS="NOTE"
300 
><BLOCKQUOTE
301 
CLASS="NOTE"
302 
><P
303 
><B
304 
>Note: </B
305 
>Exceptions at the eCos kernel level refer specifically to
306 
hardware-related events such as unaligned accesses to memory or
307 
division by zero. There is no relation with other concepts that are
308 
also known as exceptions, for example the <TT
309 
CLASS="LITERAL"
310 
>throw</TT
311 
> and
312 
<TT
313 
CLASS="LITERAL"
314 
>catch</TT
315 
> facilities associated with C++.
316 
      </P
317 
></BLOCKQUOTE
318 
></DIV
319 
></DIV
320 
><DIV
321 
CLASS="REFSECT1"
322 
><A
323 
NAME="KERNEL-EXCEPTIONS-CONTEXT"
324 
></A
325 
><H2
326 
>Valid contexts</H2
327 
><P
328 
>If the system is configured with a single set of global exception
329 
handlers then
330 
<TT
331 
CLASS="FUNCTION"
332 
>cyg_exception_set_handler</TT
333 
> and
334 
<TT
335 
CLASS="FUNCTION"
336 
>cyg_exception_clear_handler</TT
337 
> may be called during
338 
initialization or from thread context. If instead per-thread exception
339 
handlers are being used then it is not possible to install new
340 
handlers during initialization because the functions operate
341 
implicitly on the current thread, so they can only be called from
342 
thread context. <TT
343 
CLASS="FUNCTION"
344 
>cyg_exception_call_handler</TT
345 
> should
346 
only be called from thread context.
347 
      </P
348 
></DIV
349 
><DIV
350 
CLASS="NAVFOOTER"
351 
><HR
352 
ALIGN="LEFT"
353 
WIDTH="100%"><TABLE
354 
SUMMARY="Footer navigation table"
355 
WIDTH="100%"
356 
BORDER="0"
357 
CELLPADDING="0"
358 
CELLSPACING="0"
359 
><TR
360 
><TD
361 
WIDTH="33%"
362 
ALIGN="left"
363 
VALIGN="top"
364 
><A
365 
HREF="kernel-thread-destructors.html"
366 
ACCESSKEY="P"
367 
>Prev</A
368 
></TD
369 
><TD
370 
WIDTH="34%"
371 
ALIGN="center"
372 
VALIGN="top"
373 
><A
374 
HREF="ecos-ref.html"
375 
ACCESSKEY="H"
376 
>Home</A
377 
></TD
378 
><TD
379 
WIDTH="33%"
380 
ALIGN="right"
381 
VALIGN="top"
382 
><A
383 
HREF="kernel-counters.html"
384 
ACCESSKEY="N"
385 
>Next</A
386 
></TD
387 
></TR
388 
><TR
389 
><TD
390 
WIDTH="33%"
391 
ALIGN="left"
392 
VALIGN="top"
393 
>Thread destructors</TD
394 
><TD
395 
WIDTH="34%"
396 
ALIGN="center"
397 
VALIGN="top"
398 
><A
399 
HREF="kernel.html"
400 
ACCESSKEY="U"
401 
>Up</A
402 
></TD
403 
><TD
404 
WIDTH="33%"
405 
ALIGN="right"
406 
VALIGN="top"
407 
>Counters</TD
408 
></TR
409 
></TABLE
410 
></DIV
411 
></BODY
412 
></HTML
413 
>

powered by: WebSVN 2.1.0

© copyright 1999-2024 OpenCores.org, equivalent to Oliscience, all rights reserved. OpenCores®, registered trademark.