<HTML ><HEAD ><TITLE >Boot loaders are vulnerable to line noise</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="Remote Serial Console HOWTO" HREF="index.html"><LINK REL="UP" TITLE="Bugs and annoyances" HREF="bugs.html"><LINK REL="PREVIOUS" TITLE="Boot loader has no flow control" HREF="bugs-bootloaderflow.html"><LINK REL="NEXT" TITLE="Advanced Power Management" HREF="bugs-apm.html"></HEAD ><BODY CLASS="SECTION" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Remote Serial Console HOWTO</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="bugs-bootloaderflow.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Appendix A. Bugs and annoyances</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="bugs-apm.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECTION" ><H1 CLASS="SECTION" ><A NAME="BUGS-BOOTLOADERNOISE" ></A >A.9. Boot loaders are vulnerable to line noise</H1 ><P >Most boot loaders will sit at their prompt forever after receiving a single character of line noise.</P ><P >Some modems will let the <SPAN CLASS="ACRONYM" >RS-232</SPAN > signals "float", sending noise when there is no caller. Because the modem is not asserting Data Carrier Detect it expects the receiver to discard the noise characters.</P ><P >The combination of an unfortunate boot loader with an unfortunate modem can result in a machine that will regularly hang during booting.</P ><P >If you cannot configure your boot loader to obey <SPAN CLASS="ACRONYM" >DCD</SPAN > then be careful to test any modem you intend to purchase to ensure that it does not generate characters when their is no caller. At the present only <SPAN CLASS="APPLICATION" >SYSLINUX</SPAN > implements full <SPAN CLASS="ACRONYM" >RS-232</SPAN > status signals.</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="bugs-bootloaderflow.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="bugs-apm.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Boot loader has no flow control</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="bugs.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><SPAN CLASS="PRODUCTNAME" >Advanced Power Management</SPAN ></TD ></TR ></TABLE ></DIV ></BODY ></HTML >