language.values.html

encos_rtos一款精致小巧的实时嵌入式操作系统 ＋CODEWORR 教程

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></TABLE
><P
>The <TT
CLASS="VARNAME"
>CYGSEM_LIBC_PER_THREAD_RAND</TT
> option has a
<SPAN
CLASS="PROPERTY"
>requires</SPAN
> constraint on
<TT
CLASS="VARNAME"
>CYGVAR_KERNEL_THREADS_DATA</TT
>. If the C library option
is enabled then the constraint should be satisfied, or else the
configuration contains a conflict. If the configuration does not
include the kernel package then
<TT
CLASS="VARNAME"
>CYGVAR_KERNEL_THREADS_DATA</TT
> will evaluate to
<TT
CLASS="LITERAL"
>0</TT
> and the constraint is not satisfied. Similarly if
the option is inactive or disabled the constraint will not be
satisfied.</P
><P
><TT
CLASS="VARNAME"
>CYGNUM_LIBC_RAND_SEED</TT
> and
<TT
CLASS="VARNAME"
>CYGNUM_LIBC_RAND_TRACE_LEVEL</TT
> both have the
<TT
CLASS="LITERAL"
>data</TT
> flavor, so they are always enabled and the
component framework will generate appropriate
<TT
CLASS="LITERAL"
>#define's</TT
>:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#define CYGNUM_LIBC_RAND_SEED 1
#define CYGNUM_LIBC_RAND_SEED_1
#define CYGNUM_LIBC_RAND_TRACE_LEVEL 0
#define CYGNUM_LIBC_RAND_TRACE_LEVEL_0</PRE
></TD
></TR
></TABLE
><P
>Neither option has a <SPAN
CLASS="PROPERTY"
>compile</SPAN
> or similar property, but any such
properties would take effect. Any references to these options in <SPAN
CLASS="APPLICATION"
>CDL</SPAN
>
expressions would evaluate to the data part, so a hypothetical
constraint of the form
<TT
CLASS="LITERAL"
>{&nbsp;requires&nbsp;CYGNUM_LIBC_RAND_SEED&nbsp;&gt;&nbsp;42&nbsp;}</TT
>
would not be satisfied with the default values. Both options use a
simple constant for the <SPAN
CLASS="PROPERTY"
>default_value</SPAN
> expression. It would be
possible to use a more complicated expression, for example the default
for <TT
CLASS="VARNAME"
>CYGNUM_LIBC_RAND_TRACE_LEVEL</TT
> could be
determined from some global debugging option or from a debugging
option that applies to the C library as a whole. Both options also
have a <SPAN
CLASS="PROPERTY"
>legal_values</SPAN
> constraint, which must be satisfied since the
options are active and enabled. </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>The value <TT
CLASS="LITERAL"
>0</TT
> is legal for both
<TT
CLASS="VARNAME"
>CYGNUM_LIBC_RAND_SEED</TT
> and
<TT
CLASS="VARNAME"
>CYGNUM_LIBC_RAND_TRACE_LEVEL</TT
>, so in a <SPAN
CLASS="APPLICATION"
>CDL</SPAN
>
expression there is no easy way of distinguishing between the options
being absent or having that particular value. This will be addressed
by future enhancements to the expression syntax.</P
></BLOCKQUOTE
></DIV
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="LANGUAGE.EXPRESSION">Ordinary Expressions</H2
><P
>Expressions in <SPAN
CLASS="APPLICATION"
>CDL</SPAN
> follow a conventional syntax, for example:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>    default_value CYGGLO_CODESIZE &gt; CYGGLO_SPEED
    default_value { (CYG_HAL_STARTUP == "RAM" &#38;&#38;
                     !CYGDBG_HAL_DEBUG_GDB_INCLUDE_STUBS &#38;&#38;
                     !CYGINT_HAL_USE_ROM_MONITOR_UNSUPPORTED &#38;&#38;
                     !CYGSEM_HAL_POWERPC_COPY_VECTORS) ? 1 : 0 }
    default_value { "\"/dev/ser0\"" }</PRE
></TD
></TR
></TABLE
><P
>However there is a complication in that the various arguments to a
<SPAN
CLASS="PROPERTY"
>default_value</SPAN
> property will first get processed by a <SPAN
CLASS="APPLICATION"
>Tcl</SPAN
>
interpreter, so special characters like quotes and square brackets may
get processed. Such problems can be avoided by enclosing non-trivial
expressions in braces, as in the second example above. The way
expression parsing actually works is as follows:</P
><P
></P
><OL
TYPE="1"
><LI
><P
>The <SPAN
CLASS="APPLICATION"
>Tcl</SPAN
> interpreter splits the line or lines into a command and its
arguments. In the first <SPAN
CLASS="PROPERTY"
>default_value</SPAN
> expression above the command
is <TT
CLASS="LITERAL"
>default_value</TT
> and there are three arguments,
<TT
CLASS="LITERAL"
>CYGGLO_CODESIZE</TT
>, <TT
CLASS="LITERAL"
>&gt;</TT
> and
<TT
CLASS="LITERAL"
>CYGGLO_SPEED</TT
>. In the second and third examples
there is just one argument, courtesy of the braces.</P
></LI
><LI
><P
>Next option processing takes place, so any initial arguments that
begin with a hyphen will be interpreted as options. This can cause
problems if the expression involves a negative number, so the
special argument <TT
CLASS="LITERAL"
>--</TT
> can be used to prevent option
processing on the subsequent arguments.</P
></LI
><LI
><P
>All of the arguments are now concatenated, with a single space in
between each one. Hence the following two expressions are equivalent,
even though they will have been processed differently up to this point.</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>    default_value CYGGLO_CODESIZE &gt; CYGGLO_SPEED
    default_value {CYGGLO_CODESIZE &gt; CYGGLO_SPEED}</PRE
></TD
></TR
></TABLE
></LI
><LI
><P
>The expression parsing code now has a single string to process.</P
></LI
></OL
><P
><SPAN
CLASS="APPLICATION"
>CDL</SPAN
> expressions consist of four types of element: references to
configuration options, constant strings, integers, and floating point
numbers. These are combined using a conventional set of operators: the
unary operators <TT
CLASS="LITERAL"
>-</TT
>, <TT
CLASS="LITERAL"
>~</TT
> and
<TT
CLASS="LITERAL"
>!</TT
>; the arithmetic operators <TT
CLASS="LITERAL"
>+</TT
>,
<TT
CLASS="LITERAL"
>-</TT
>, <TT
CLASS="LITERAL"
>*</TT
>, <TT
CLASS="LITERAL"
>/</TT
> and
<TT
CLASS="LITERAL"
>%</TT
>; the shift operators <TT
CLASS="LITERAL"
>&lt;&lt;</TT
>
and <TT
CLASS="LITERAL"
>&gt;&gt;</TT
>; the comparison operators
<TT
CLASS="LITERAL"
>==</TT
>, <TT
CLASS="LITERAL"
>!=</TT
>, <TT
CLASS="LITERAL"
>&lt;</TT
>,
<TT
CLASS="LITERAL"
>&lt;=</TT
>, <TT
CLASS="LITERAL"
>&gt;</TT
> and
<TT
CLASS="LITERAL"
>&gt;=</TT
>; the bitwise operators
<TT
CLASS="LITERAL"
>&amp;</TT
>, <TT
CLASS="LITERAL"
>^</TT
> and
<TT
CLASS="LITERAL"
>|</TT
>; the logical operators <TT
CLASS="LITERAL"
>&#38;&#38;</TT
> and
<TT
CLASS="LITERAL"
>||</TT
>; the string concatenation operator
<TT
CLASS="LITERAL"
>.</TT
>; and the ternary conditional operator
<TT
CLASS="LITERAL"
>A&nbsp;?&nbsp;B&nbsp;:&nbsp;C</TT
>. There is also support for
some less widely available operators for logical equivalence and
implication, and for a set of function-style operations. Bracketed
sub-expressions are supported, and the operators have the usual
precedence:</P
><DIV
CLASS="INFORMALTABLE"
><A
NAME="AEN1653"><P
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><THEAD
><TR
><TH
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>Priority</TH
><TH
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>Operators</TH
><TH
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>Category</TH
></TR
></THEAD
><TBODY
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>16</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>references, constants</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>basic elements</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>15</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>f(a, b, c)</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>function calls</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>14</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>~</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>bitwise not</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>14</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>!</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>logical not</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>14</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>-</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>arithmetic negation</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>13</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>* / %</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>multiplicative arithmetic</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>12</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>+ - .</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>additive arithmetic and string concatenation</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>11</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>&lt;&lt; &gt;&gt;</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>bitwise shifts</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>10</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>&lt;= &lt; &gt; &gt;=</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>inequality</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>9</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>== !=</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>comparison</TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>8</TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
><TT
CLASS="LITERAL"
>&#38;</TT
></TD
><TD
WIDTH="33%"
ALIGN="CENTER"
VALIGN="TOP"
>bitwise and</TD
></TR