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86 lines
3.8 KiB
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86 lines
3.8 KiB
HTML
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<link href="GDB.html#GDB" rel="up" title="GDB">
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<link href="ROM-monitors.html#ROM-monitors" rel="next" title="ROM monitors">
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<link href="GNU-remote-protocol.html#GNU-remote-protocol" rel="prev" title="GNU remote protocol">
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<a name="Exception-handler"></a>
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<div class="header">
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<p>
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Next: <a href="ROM-monitors.html#ROM-monitors" accesskey="n" rel="next">ROM monitors</a>, Previous: <a href="GNU-remote-protocol.html#GNU-remote-protocol" accesskey="p" rel="prev">GNU remote protocol</a>, Up: <a href="GDB.html#GDB" accesskey="u" rel="up">GDB</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="A-linked-in-exception-handler"></a>
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<h3 class="section">4.2 A linked in exception handler</h3>
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<p>A <em>GDB stub</em> consists of two parts, support for the exception
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handler, and the exception handler itself. The exception handler needs
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to communicate to GDB on the host whenever there is a breakpoint
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exception. When GDB starts a program running on the target, it’s polling
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the serial port during execution looking for any debug packets. So when
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a breakpoint occurs, the exception handler needs to save state, and send
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a GDB remote protocol packet to GDB on the host. GDB takes any output
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that isn’t a debug command packet and displays it in the command window.
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</p>
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<p>Support for the exception handler varies between processors, but the
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minimum supported functions are those needed by GDB. These are functions
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to support the reading and writing of registers, the reading and writing
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of memory, start execution at an address, single step, and last signal.
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Sometimes other functions for adjusting the baud rate, or resetting the
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hardware are implemented.
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</p>
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<p>Once GDB gets the command packet from the breakpoint, it will read a few
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registers and memory locations an then wait for the user. When the user
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types <code>run</code> or <code>continue</code> a <code>continue</code> command is issued
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to the backend, and control returns from the breakpoint routine to the
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application.
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</p>
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</body>
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</html>
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