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>HAL Coding Conventions</TITLE
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>eCos Reference Manual</TH
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><A
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>Prev</A
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><TD
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 11. Porting Guide</TD
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CLASS="SECTION"
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><H1
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CLASS="SECTION"
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><A
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NAME="HAL-PORTING-CODING-CONVENTIONS">HAL Coding Conventions</H1
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><P
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>To get changes and larger submissions included into the eCos source
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repository, we ask that you adhere to a set of coding conventions.
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The conventions are defined as an attempt to make a consistent
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tree. Consistency makes it easier for people to read, understand and
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maintain the code, which is important when many people work on the
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same project.</P
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><P
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>The below is only a brief, and probably incomplete, summary of the
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rules. Please look through files in the area where you are making
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changes to get a feel for any additional conventions. Also feel free
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to ask on the list if you have specific questions.</P
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><DIV
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CLASS="SECTION"
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><H2
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CLASS="SECTION"
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><A
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NAME="AEN9361">Implementation issues</H2
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><P
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>There are a few implementation issues that should be kept in mind:</P
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><P
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></P
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><DIV
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CLASS="VARIABLELIST"
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><DL
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><DT
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>HALs</DT
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><DD
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><P
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>HALs must be written in C and assembly only. C++ must not
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        be used. This is in part to keep the HALs simple since this is
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        usually the first part of eCos a newcomer will see, and in
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        part to maintain the existing de facto standard.</P
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></DD
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><DT
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>IO access</DT
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><DD
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><P
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>Use HAL IO access macros for code that might be reused on
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        different platforms than the one you are writing it for.</P
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></DD
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><DT
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>MMU</DT
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><DD
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><P
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>If it is necessary to use the MMU (e.g., to prevent
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        caching of IO areas), use a simple 1-1 mapping of memory if
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        possible. On most platforms where using the MMU is necessary,
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        it will be possible to achieve the 1-1 mapping using the MMU's
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        provision for mapping large continuous areas (hardwired TLBs or
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        BATs). This reduces the footprint (no MMU table) and avoids
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        execution overhead (no MMU-related exceptions).</P
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></DD
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><DT
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>Assertions</DT
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><DD
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><P
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>The code should contain assertions to validate argument
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        values, state information and any assumptions the code may be
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        making. Assertions are not enabled in production builds, so
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        liberally sprinkling assertions throughout the code is
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        good.</P
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></DD
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><DT
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>Testing</DT
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><DD
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><P
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>The ability to test your code is very important. In
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        general, do not add new code to the eCos runtime unless you
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        also add a new test to exercise that code. The test also
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        serves as an example of how to use the new code.</P
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></DD
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></DL
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></DIV
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></DIV
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><DIV
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CLASS="SECTION"
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><H2
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CLASS="SECTION"
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><A
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NAME="AEN9385">Source code details</H2
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><P
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></P
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><DIV
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CLASS="VARIABLELIST"
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><DL
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><DT
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>Line length</DT
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><DD
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><P
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>Keep line length below 78 columns whenever possible.</P
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></DD
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><DT
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>Comments</DT
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><DD
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><P
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>Whenever possible, use // comments instead of /**/.</P
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></DD
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><DT
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>Indentation</DT
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><DD
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><P
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>Use spaces instead of TABs. Indentation level is 4. Braces
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        start on the same line as the expression. See below for emacs
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        mode details.</P
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><TABLE
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>;;=================================================================
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;; eCos C/C++ mode Setup.
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;;
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;; bsd mode: indent = 4
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;; tail comments are at col 40.
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;; uses spaces not tabs in C
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(defun ecos-c-mode ()
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  "C mode with adjusted defaults for use with the eCos sources."
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  (interactive)
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  (c++-mode)
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  (c-set-style "bsd")
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  (setq comment-column 40)
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  (setq indent-tabs-mode nil)
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  (show-paren-mode 1)
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  (setq c-basic-offset 4)
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  (set-variable 'add-log-full-name "Your Name")
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  (set-variable 'add-log-mailing-address "Your email address"))
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(defun ecos-asm-mode ()
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  "ASM mode with adjusted defaults for use with the eCos sources."
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  (interactive)
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  (setq comment-column 40)
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  (setq indent-tabs-mode nil)
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  (asm-mode)
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  (setq c-basic-offset 4)
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  (set-variable 'add-log-full-name "Your Name")
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  (set-variable 'add-log-mailing-address "Your email address"))
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(setq auto-mode-alist
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      (append '(("/local/ecc/.*\\.C$"   . ecos-c-mode)
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                ("/local/ecc/.*\\.cc$"  . ecos-c-mode)
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                ("/local/ecc/.*\\.cpp$" . ecos-c-mode)
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                ("/local/ecc/.*\\.inl$" . ecos-c-mode)
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                ("/local/ecc/.*\\.c$"   . ecos-c-mode)
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                ("/local/ecc/.*\\.h$"   . ecos-c-mode)
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                ("/local/ecc/.*\\.S$"   . ecos-asm-mode)
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                ("/local/ecc/.*\\.inc$" . ecos-asm-mode)
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                ("/local/ecc/.*\\.cdl$" . tcl-mode)
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                ) auto-mode-alist))</PRE
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></DIV
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><DIV
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CLASS="SECTION"
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><H2
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CLASS="SECTION"
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><A
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NAME="AEN9401">Nested Headers</H2
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><P
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>In order to allow platforms to define all necessary details, while
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still maintaining the ability to share code between common platforms,
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all HAL headers are included in a nested fashion.</P
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><P
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>The architecture header (usually <TT
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CLASS="FILENAME"
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>hal_XXX.h</TT
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>) includes the
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variant equivalent of the header (<TT
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CLASS="FILENAME"
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>var_XXX.h</TT
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>) which in turn
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includes the platform equivalent of the header
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(<TT
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CLASS="FILENAME"
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>plf_XXX.h</TT
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>).</P
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><P
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>All definitions that may need to be overridden by a platform are
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then only conditionally defined, depending on whether a lower layer
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has already made the definition:</P
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><TABLE
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>hal_intr.h:     #include &lt;var_intr.h&gt;
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                #ifndef MACRO_DEFINED
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                # define MACRO ...
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                # define MACRO_DEFINED
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                #endif
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var_intr.h:     #include &lt;plf_intr.h&gt;
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                #ifndef MACRO_DEFINED
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                # define MACRO ...
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                # define MACRO_DEFINED
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                #endif
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plf_intr.h:
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                # define MACRO ...
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                # define MACRO_DEFINED</PRE
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></TD
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></TR
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></TABLE
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><P
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>This means a platform can opt to rely on the variant or
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architecture implementation of a feature, or implement it itself.</P
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>Virtual Vectors (eCos/ROM Monitor Calling Interface)</TD
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>Up</A
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>Platform HAL Porting</TD
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