flwctl.htm

mips架构的bootloader,99左右的版本 但源代码现在没人更新了

		<title> Flow Control </title>
		<h1 align=center>Flow Control</h1>

<!--INDEX "Flow control" dlproto dlecho Xon-Xoff Etx-Ack -->

A flow-control protocol is selected to ensure that the host does not
send data too fast for the target to receive. The need for this can
arise because, although the target system may be able to read a record
at 9600 baud, the target system may need time to process that record
before it can read the next record.<p>

The environment variables dlproto and dlecho are used specify the
flow-control protocol.<p>

The following table summarizes the four flow-control protocols supported by
this <a href="mondef.htm">Monitor</a>.<p>

<table border cellpadding=5>
<tr>
<th>Terminal Emulator Sends</th><th>Target Returns</th><th>Set</th><th>Application</th>
</tr>

<tr>
<td valign=top> Line terminated by carriage return</td>
<td valign=top>Echoes same line</td>
<td valign=top nowrap><tt>
dlecho = on<br>
dlproto = none<tt></td>
<td valign=top>
Terminal Emulator waits for full line to be echoed before sending next line.
</td>
</tr>

<tr>
<td valign=top> Line terminated by carriage return</td>
<td valign=top>Returns line-feed character</td>
<td valign=top nowrap><tt>
dlecho = lfeed<br>
dlproto = none<tt></td>
<td valign=top>
Terminal Emulator waits for line-feed to be echoed before sending next line.
</td>
</tr>

<tr>
<td valign=top> Line terminated by carriage return</td>
<td valign=top>Returns Xoff and Xon characters</td>
<td valign=top nowrap><tt>
dlecho = off<br>
dlproto = XonXoff<tt></td>
<td valign=top>
Terminal Emulator sends until Xoff. Resumes sending after Xon.
</td>
</tr>

<tr>
<td valign=top> Line terminated by ETX character</td>
<td valign=top>Returns Ack character</td>
<td valign=top nowrap><tt>
dlecho = off<br>
dlproto = EtxAck<tt></td>
<td valign=top>
Terminal Emulator sends line terminated by Etx. Sends next line after Ack
(see note).
</td>
</tr>

</table><p>

<b>Note:</b>
The Xon-Xoff protocol is often not as reliable a method of flow-control
as it might first appear. This is because
many host systems do not shut off the flow
of characters immediately upon receiving an Xoff. They may continue
to transmit 20 or 30 bytes before finally stopping. Unfortunately these
characters will not be seen by the monitor because it is not interrupt
driven, and will be busy processing the previous line.<p>

</dl><p><hr>
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