c_b.htm

mips架构的bootloader,99左右的版本 但源代码现在没人更新了

<title>The b Command</title>
<h1>b</h1>

<!--INDEX "breakpoint number" brkcmd "b command" -->

The b command sets and displays breakpoints.<p>

</dl><h2>Format</h2><dl><dd>

The format for the b command is:<p>

<pre>
b
b <var>adr..</var>
b <var>adr</var> -s <var>str</var>
</pre><p>

where:<p>

<table>
<tr>
<td width=50><var>adr</var></td><td>	specifies an address for the breakpoint. 
				Up to 32 breakpoints addresses can be set.
</td></tr><tr>
<td>-s <var>str</var></td><td>	executes the command string when the breakpoint is hit.
</td></tr>
</table><p>

Invoking the b command with no options causes the <a href="mondef.htm">Monitor</a> to print a list 
of the current breakpoints. <p>

</dl><h2>Functional Description</h2><dl><dd>

The b command sets a breakpoint at the specified 
address or addresses. Multiple addresses may be specified. Specified 
addresses must be word-aligned. <p>

This command is effectively a "pass-thru" to the 
<a href="c_when.htm">when</a> command. Issuing the command, 
"<samp>b main</samp>" is equivalent to issuing the command, 
"<samp>when @pc==main stop</samp>". However, unlike the 
<samp>when</samp> command, the <samp>b</samp> command can
take multiple addresses.<p>

The <a href="mondef.htm">Monitor</a> automatically assigns a number to each breakpoint. 
The <a href="mondef.htm">Monitor</a> allocates the lowest 
available breakpoint number from 0 to 31 to any new breakpoint. <p>

The <a href="mondef.htm">Monitor</a> reports a new breakpoint's number immediately after the 
breakpoint is set (see the examples at the end of this subsection for 
illustration of this). The assigned numbers can be used in the 
<a href="c_db.htm">db</a> (Delete Breakpoint) command.<p>

<b>The brkcmd Variable </b><p>

When a breakpoint is reached, the command list specified in the 
environment variable brkcmd is executed. The default setting for brkcmd is:<p>

<pre>
brkcmd = "l @pc 1"
</pre>

This command "<samp>l @pc 1</samp>", specifies that when the breakpoint
occurs, the <a href="mondef.htm">Monitor</a> will disassemble one line starting at the address
of the program counter.<p>

You can change the breakpoint command variable with the set command. 
For example, you can include additional monitor commands in the brkcmd 
variable. You must separate additional commands on the command line 
with a semicolon. For example, entering the following command lists one 
line after reaching a breakpoint, and then displays all the register values.<p>

<pre>
set brkcmd "l @epc 1;r *"
</pre>

By default, breakpoints are cleared when the load command is executed. 
See the section on the load command later in this document for details on 
how to override automatic breakpoint clearing after a download operation.<p>

Some examples illustrating the use of the b command follow.<p>

<table>
<tr><td><samp>
PMON> b a002000c	</samp></td><td>Set a breakpoint at 0xa002000c.
</td></tr>

<tr><td><samp>
Bpt 1 = a002000c
</td></tr>

<tr><td><samp>
PMON> b			<br>
Bpt 0 = 8002022c<br>
Bpt 1 = a002000c
</samp></td><td valign=top>Display all breakpoints.
</td></tr>

<tr><td valign=top><samp>
PMON> b 80021248 -s "r"	</samp></td><td>Set a breakpoint at 0x80021248. Display registers
			when the breakpoint is encountered.
</td></tr>
</table>
<p>


</dl><h2>See Also </h2><dl><dd>
<a href="c_db.htm">db</a>,
<a href="c_when.htm">when</a>, 
and <a href="c_load.htm">load</a> commands.

</dl><p><hr>
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