c_ab.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 ab Command</title>
<h1>ab</h1>

<!--INDEX "breakpoint number" brkcmd "ab command" "data breakpoint" -->
<!--INDEX "access breakpoint" mask -->

The ab command sets data (access) breakpoints.<p>

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

The format for the ab command is:<p>

<pre>
ab [-rw] <var>adr</var> [<var>mask</var>]
</pre><p>

where:<p>

<table>
<tr>
<td width=50><var>adr</var></td><td>	
	specifies an address for the breakpoint. </td></tr>
<td><var>mask</var></td><td>	
	specifies an address optional mask. </td></tr>
<tr><td>-r </td><td>stop on a read access only</td></tr>
<tr><td>-w </td><td>stop on a write access only</td></tr>
</table><p>

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

The ab command sets a data breakpoint at the specified 
address. Specified addresses must be word-aligned. By default
execution will stop if there is a read or write to the specified
address. However, the -r and -w options may be used to limit the
break condition to either reads or writes respectively. A mask may
be used to specify that a data breakpoint should occur over a range
of addresses. In this case a zero bit in the mask excludes the
corresponding address bit from the address comparison.<p>

Because this command requires hardware support in the CPU that you are
debugging, the number of data breakpoints is likely to be very limited.
<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 ab command follow.<p>

<table>
<tr><td><samp>
PMON> ab a002000c	</samp></td><td align=top>
Set a breakpoint at 0xa002000c.
</td></tr>

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

<tr><td valign=top><samp>
PMON> ab -w 80021248 </samp></td><td align=top>Stop on a write to 0x80021248.
</td></tr>

<tr><td valign=top><samp>
PMON> ab 80021200 ffffff00 </samp></td><td align=top>
Stop on an access to any address in the range 0x80021200 thru 0x800212ff.
</td></tr>

</table> <p> 

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

</dl><p><hr>
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