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107 lines
5.1 KiB
HTML
107 lines
5.1 KiB
HTML
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<link href="index.html#Top" rel="start" title="Top">
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<link href="leds_002ec.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Libraries.html#Libraries" rel="up" title="Libraries">
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<link href="I_002fO-Support.html#I_002fO-Support" rel="next" title="I/O Support">
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<link href="What-to-do-now.html#What-to-do-now" rel="prev" title="What to do now">
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<a name="Libc"></a>
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<div class="header">
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<p>
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Previous: <a href="What-to-do-now.html#What-to-do-now" accesskey="p" rel="prev">What to do now</a>, Up: <a href="Libraries.html#Libraries" accesskey="u" rel="up">Libraries</a> [<a href="leds_002ec.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
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</div>
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<hr>
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<a name="Libraries-1"></a>
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<h3 class="section">3.4 Libraries</h3>
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<p>This describes <code>newlib</code>, a freely available libc replacement. Most
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applications use calls in the standard C library. When initially linking
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in libc.a, several I/O functions are undefined. If you don’t plan on
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doing any I/O, then you’re OK, otherwise they need to be created. These
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routines are read, write, open, close. sbrk, and kill. Open & close
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don’t need to be fully supported unless you have a filesystems, so
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typically they are stubbed out. Kill is also a stub, since you can’t do
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process control on an embedded system.
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</p>
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<p>Sbrk() is only needed by applications that do dynamic memory
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allocation. It’s uses the symbol <code>_end</code> that is setup in the linker
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script. It also requires a compile time option to set the upper size
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limit on the heap space. This leaves us with read and write, which are
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required for serial I/O. Usually these two routines are written in C,
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and call a lower level function for the actual I/O operation. These two
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lowest level I/O primitives are inbyte() and outbyte(), and are also
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used by GDB back ends if you’ve written an exception handler. Some
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systems also implement a havebyte() for input as well.
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</p>
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<p>Other commonly included functions are routines for manipulating
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LED’s on the target (if they exist) or low level debug help. Typically a
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putnum() for printing words and bytes as a hex number is helpful, as
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well as a low-level print() to output simple strings.
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</p>
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<p>As libg++ uses the I/O routines in libc.a, if read and write work,
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then libg++ will also work with no additional changes.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="I_002fO-Support.html#I_002fO-Support" accesskey="1">I/O Support</a>:</td><td> </td><td align="left" valign="top">Functions that make serial I/O work.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Memory-Support.html#Memory-Support" accesskey="2">Memory Support</a>:</td><td> </td><td align="left" valign="top">Memory support.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Misc-Support.html#Misc-Support" accesskey="3">Misc Support</a>:</td><td> </td><td align="left" valign="top">Other needed functions.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Debugging.html#Debugging" accesskey="4">Debugging</a>:</td><td> </td><td align="left" valign="top">Useful Debugging Functions
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="What-to-do-now.html#What-to-do-now" accesskey="p" rel="prev">What to do now</a>, Up: <a href="Libraries.html#Libraries" accesskey="u" rel="up">Libraries</a> [<a href="leds_002ec.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
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