+++ /dev/null
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-<HTML
-><HEAD
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->Exception handling</TITLE
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-TITLE="The eCos Kernel"
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-TITLE="Thread destructors"
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-><H1
-><A
-NAME="KERNEL-EXCEPTIONS">Exception handling</H1
-><DIV
-CLASS="REFNAMEDIV"
-><A
-NAME="AEN782"
-></A
-><H2
->Name</H2
->cyg_exception_set_handler, cyg_exception_clear_handler, cyg_exception_call_handler -- Handle processor exceptions</DIV
-><DIV
-CLASS="REFSYNOPSISDIV"
-><A
-NAME="AEN787"><H2
->Synopsis</H2
-><DIV
-CLASS="FUNCSYNOPSIS"
-><A
-NAME="AEN788"><P
-></P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="FUNCSYNOPSISINFO"
->#include <cyg/kernel/kapi.h>
- </PRE
-></TD
-></TR
-></TABLE
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_exception_set_handler</CODE
->(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
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_exception_clear_handler</CODE
->(cyg_code_t exception_number);</CODE
-></P
-><P
-><CODE
-><CODE
-CLASS="FUNCDEF"
->void cyg_exception_call_handler</CODE
->(cyg_handle_t thread, cyg_code_t exception_number, cyg_addrword_t exception_info);</CODE
-></P
-><P
-></P
-></DIV
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="AEN817"
-></A
-><H2
->Description</H2
-><P
->Sometimes code attempts operations that are not legal on the current
-hardware, for example dividing by zero, or accessing data through a
-pointer that is not properly aligned. When this happens the hardware
-will raise an exception. This is very similar to an interrupt, but
-happens synchronously with code execution rather than asynchronously
-and hence can be tied to the thread that is currently running.
- </P
-><P
->The exceptions that can be raised depend very much on the hardware,
-especially the processor. The corresponding documentation should be
-consulted for more details. Alternatively the architectural HAL header
-file <TT
-CLASS="FILENAME"
->hal_intr.h</TT
->, or one of the
-variant or platform header files it includes, will contain appropriate
-definitions. The details of how to handle exceptions, including
-whether or not it is possible to recover from them, also depend on the
-hardware.
- </P
-><P
->Exception handling is optional, and can be disabled through the
-configuration option <TT
-CLASS="VARNAME"
->CYGPKG_KERNEL_EXCEPTIONS</TT
->. If
-an application has been exhaustively tested and is trusted never to
-raise a hardware exception then this option can be disabled and code
-and data sizes will be reduced somewhat. If exceptions are left
-enabled then the system will provide default handlers for the various
-exceptions, but these do nothing. Even the specific type of exception
-is ignored, so there is no point in attempting to decode this and
-distinguish between say a divide-by-zero and an unaligned access.
-If the application installs its own handlers and wants details of the
-specific exception being raised then the configuration option
-<TT
-CLASS="VARNAME"
->CYGSEM_KERNEL_EXCEPTIONS_DECODE</TT
-> has to be enabled.
- </P
-><P
->An alternative handler can be installed using
-<TT
-CLASS="FUNCTION"
->cyg_exception_set_handler</TT
->. This requires a code
-for the exception, a function pointer for the new exception handler,
-and a parameter to be passed to this handler. Details of the
-previously installed exception handler will be returned via the
-remaining two arguments, allowing that handler to be reinstated, or
-null pointers can be used if this information is of no interest. An
-exception handling function should take the following form:
- </P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->void
-my_exception_handler(cyg_addrword_t data, cyg_code_t exception, cyg_addrword_t info)
-{
- …
-}
- </PRE
-></TD
-></TR
-></TABLE
-><P
->The data argument corresponds to the <TT
-CLASS="PARAMETER"
-><I
->new_data</I
-></TT
->
-parameter supplied to <TT
-CLASS="FUNCTION"
->cyg_exception_set_handler</TT
->.
-The exception code is provided as well, in case a single handler is
-expected to support multiple exceptions. The <TT
-CLASS="PARAMETER"
-><I
->info</I
-></TT
->
-argument will depend on the hardware and on the specific exception.
- </P
-><P
-><TT
-CLASS="FUNCTION"
->cyg_exception_clear_handler</TT
-> can be used to
-restore the default handler, if desired. It is also possible for
-software to raise an exception and cause the current handler to be
-invoked, but generally this is useful only for testing.
- </P
-><P
->By default the system maintains a single set of global exception
-handlers. However, since exceptions occur synchronously it is
-sometimes useful to handle them on a per-thread basis, and have a
-different set of handlers for each thread. This behaviour can be
-obtained by disabling the configuration option
-<TT
-CLASS="VARNAME"
->CYGSEM_KERNEL_EXCEPTIONS_GLOBAL</TT
->. If per-thread
-exception handlers are being used then
-<TT
-CLASS="FUNCTION"
->cyg_exception_set_handler</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_exception_clear_handler</TT
-> apply to the current
-thread. Otherwise they apply to the global set of handlers.
- </P
-><DIV
-CLASS="CAUTION"
-><P
-></P
-><TABLE
-CLASS="CAUTION"
-BORDER="1"
-WIDTH="100%"
-><TR
-><TD
-ALIGN="CENTER"
-><B
->Caution</B
-></TD
-></TR
-><TR
-><TD
-ALIGN="LEFT"
-><P
->In the current implementation
-<TT
-CLASS="FUNCTION"
->cyg_exception_call_handler</TT
-> can only be used on
-the current thread. There is no support for delivering an exception to
-another thread.
- </P
-></TD
-></TR
-></TABLE
-></DIV
-><DIV
-CLASS="NOTE"
-><BLOCKQUOTE
-CLASS="NOTE"
-><P
-><B
->Note: </B
->Exceptions at the eCos kernel level refer specifically to
-hardware-related events such as unaligned accesses to memory or
-division by zero. There is no relation with other concepts that are
-also known as exceptions, for example the <TT
-CLASS="LITERAL"
->throw</TT
-> and
-<TT
-CLASS="LITERAL"
->catch</TT
-> facilities associated with C++.
- </P
-></BLOCKQUOTE
-></DIV
-></DIV
-><DIV
-CLASS="REFSECT1"
-><A
-NAME="KERNEL-EXCEPTIONS-CONTEXT"
-></A
-><H2
->Valid contexts</H2
-><P
->If the system is configured with a single set of global exception
-handlers then
-<TT
-CLASS="FUNCTION"
->cyg_exception_set_handler</TT
-> and
-<TT
-CLASS="FUNCTION"
->cyg_exception_clear_handler</TT
-> may be called during
-initialization or from thread context. If instead per-thread exception
-handlers are being used then it is not possible to install new
-handlers during initialization because the functions operate
-implicitly on the current thread, so they can only be called from
-thread context. <TT
-CLASS="FUNCTION"
->cyg_exception_call_handler</TT
-> should
-only be called from thread context.
- </P
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