<HTML ><HEAD ><TITLE >The development environment of Etherboot</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" HREF="t1.html"><LINK REL="PREVIOUS" TITLE="The architecture of Etherboot" HREF="x169.html"><LINK REL="NEXT" TITLE="Frequently asked questions" HREF="x295.html"></HEAD ><BODY CLASS="sect1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="x169.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="x295.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="sect1" ><H1 CLASS="sect1" ><A NAME="AEN233" ></A >The development environment of Etherboot</H1 ><P > Etherboot is written in C, with certain routines written in x86 assembler for access to machine resources or to do things not possible in C. The tools used are the GNU C compiler and GNU x86 assembler. <B CLASS="command" >ld</B > is used to link the object files. An auxiliary program called <B CLASS="command" >makerom.pl</B > converts this binary into a form suitable for writing into a ROM. </P ><P > A Makefile coordinates all the building procedures. However there are many network adapters that differ only in the PCI vendor and device IDs. This information must be programmed into the ROM header using <B CLASS="command" >makerom</B >. An auxiliary script called <B CLASS="command" >genrules.pl</B > scans all driver source files for the device names and IDs and outputs make rules to a file called <TT CLASS="filename" >Roms</TT > that is included by the main Makefile to generate all the ROM images. Another file included by Makefile is <TT CLASS="filename" >Config</TT >, which contains user configurable build parameters. </P ><P > Let us take an example of a ROM image that we could build, <TT CLASS="filename" >bin/mx98715.zrom</TT >. According to this line in the file <TT CLASS="filename" >tulip.c</TT >: <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="programlisting" > PCI_ROM(0x10d9, 0x0531, "mx98715", "Macronix MX987x5"), </PRE ></TD ></TR ></TABLE > the driver code is in <TT CLASS="filename" >tulip.c</TT > and the vendor ID is 0x10d9 and the device ID is 0x0531. If one were to say <B CLASS="command" >make bin/mx98715.zrom</B >, the following actions happen: </P ><P > <P ></P ><UL ><LI ><P > Any needed utilities such as <TT CLASS="filename" >bin/nrv2b</TT > are built. </P ></LI ><LI ><P > <TT CLASS="filename" >drivers/net/tulip.c</TT > is compiled to <TT CLASS="filename" >bin/tulip.o</TT >. </P ></LI ><LI ><P > The startup routine, <TT CLASS="filename" >arch/i386/core/start32.S</TT > is assembled to <TT CLASS="filename" >bin/start32.o</TT >. </P ></LI ><LI ><P > All the core Etherboot files, e.g. <TT CLASS="filename" >core/main.c</TT >, <TT CLASS="filename" >osloader.c</TT >, etc, are compiled to corresponding object files in <TT CLASS="filename" >bin/*.o</TT > and combined into an ar archive, <TT CLASS="filename" >bin/bootlib.a</TT >, for convenience. </P ></LI ><LI ><P > The startup routine (which must be first in the list of objects), the driver object, <TT CLASS="filename" >bootlib.a</TT >, the platform specific objects are linked to produce an ELF binary, linked to run at the relocation address of Etherboot, currently 0x20000. The ELF binary is converted to an Etherboot binary using GNU utilities. This binary is can be on non-x86 platforms by conversions. (To fill in later.) For the x86 platform, we need to prepend loaders for the chosen load method. </P ></LI ><LI ><P > The prepended ROM loaders, rloader, and prloader, are produced by assembling <TT CLASS="filename" >arch/i386/prefix/loader.S</TT > with different defines. The meaning of the prefixes are: rloader = basic ROM loader, and prloader = PCI header basic ROM loader. The loaders contain the needed headers for the BIOS to recognise the code as an extension ROM. See <A HREF="extension.html" >the Section called <I >The execution environment of Etherboot</I ></A > on the extension BIOS mechanism. </P ></LI ><LI ><P > For example, in the case of <TT CLASS="filename" >bin/mx987x5.zrom</TT >, this is for a PCI adaptor and we want a compressed ROM, so the loader is prloader. This is prepended to the Etherboot image to generate a ROM image. </P ></LI ><LI ><P > <B CLASS="command" >makerom.pl</B > is run over this ROM image to pad it to the size of a standard EPROM. (8 kB, 16 kB, 32 kB, etc.) The PCI IDs are written into the image into the PnP structure at the right spots. A string identifying the device and Etherboot version is written into the unprogrammed bytes at the end of the ROM image, if space is available, and a pointer to that written into the PnP structure. The vendor string and the device string are normally printed by the PCI PnP BIOS at boot time. Makerom also calculates the checksum (both for the PnP structure, if present and for the whole image) and alters designated spare bytes in the image so that the checksums come out right. The image is then ready to be written into an EPROM. </P ></LI ><LI ><P > By prepending alternate loaders to the Etherboot image, we can load the image from floppy, LILO/SYSLINUX, PXE or DOS. In the case of floppy loading, the preloader is called <TT CLASS="filename" >floppyload.bin</TT >. It is one sector (512 bytes) long and loaded from the floppy, starting at the beginning of the floppy. It then loads the blocks following itself, which it assumes to be an Etherboot image, into memory, then jumps to the start of it. </P ><P > In the case of LILO/SYSLINUX booting, the preloader is <TT CLASS="filename" >bin/liloprefix.bin</TT >. It contains what looks like a floppy sector and a startup segment to LILO/SYSLINUX and makes LILO/SYSLINUX "think" that this is a Linux kernel. </P ></LI ><LI ><P > The loader for chaining from PXE is in <TT CLASS="filename" >bin/pxeprefix.bin</TT >, and when prepended to an image, produces a file that can be downloaded and executed by a PXE conforming boot rom as a first stage loader. Etherboot then takes over the remainder of the load process. </P ></LI ><LI ><P > Yet another preloader is not for a device but for an OS environment. This is <TT CLASS="filename" >bin/comprefix.bin</TT >, and when prepended to an image, makes it look like a DOS .com executable, including the peculiarity of starting at COM_SEGMENT:0x100. All it does however is jump to the Etherboot image. </P ></LI ><LI ><P > All the preceeding special preloaders have associated Makefile rules and are created by asking for images with the appropriate suffix. For example, if one wanted an image for writing onto a floppy one would say: <TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" ><TR ><TD ><PRE CLASS="programlisting" > make bin/mx98715.zdsk </PRE ></TD ></TR ></TABLE > </P ></LI ></UL > </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="x169.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="t1.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="x295.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >The architecture of Etherboot</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Frequently asked questions</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
