Running Etherboot within Bochs
==============================

Michael Brown <mbrown@fensystems.co.uk>
Based on an idea suggested by H. Peter Anvin <hpa@zytor.com>.

$Id$

Bochs is a program that simulates a complete Intel x86 computer,
including hardware.  It can be used to test Etherboot.  There is a
special pseudo NIC ("pnic") implemented in Bochs, with a corresponding
driver in Etherboot.  (There is also an NE2000 ISA driver in Bochs,
but it doesn't seem to quite work.)

To get bochs running is fairly simple:

1.  Get the bochs source code:
    a)  cvs -d:pserver:anonymous:@cvs.sourceforge.net:/cvsroot/bochs login
    b)  cvs -d:pserver:anonymous:@cvs.sourceforge.net:/cvsroot/bochs co bochs

2.  Configure bochs with
      ./configure --enable-all-optimisations --enable-pci \
	 	 --enable-ne2000 --enable-pnic
    Other potentially useful configure options:
      --prefix=/usr
          to force use of standard file locations
      --enable-debugger
          to enable the internal debugger

3.  Build bochs:
      make

4.  Configure Etherboot with CONFIG_PCI_DIRECT: add the line
      CFLAGS += -DCONFIG_PCI_DIRECT
    to the end of src/arch/i386/Config.

5.  Build bin/pnic.zrom:
      make bin/pnic.zrom

6.  Load the TUN/TAP kernel module:
      modprobe tun
    You should see the device /dev/net/tun is created automatically if
    you're using devfs, otherwise you may have to create it by hand with:
      mknod /dev/net/tun c 10 200

7.  Grant yourself write access to /dev/net/tun:
      su -c 'chown <your user id> /dev/net/tun'
    The alternative to this is to run Bochs as root.  Don't do that.

8.  Add the following fragment to /etc/dhcpd.conf:
      subnet 10.254.254.0 netmask 255.255.255.252 {
        range dynamic-bootp 10.254.254.1 10.254.254.1;
      }
    You will also need to add in any of your usual declarations for
    Etherboot, e.g. 'filename "vmlinuz.ltsp";'.  Note that this setup
    assumes that your DHCP server, TFTP server etc. all live on the
    machine you are using for running Bochs.  If not, then you're on
    your own.

9.  Change back to this directory and run bochs from your Bochs source tree:
      cd /path/to/Etherboot/contrib/bochs
      /path/to/bochs/source/tree/bochs

10. Select option 5 (Begin simulation).  You will be prompted for your
    root password.  This is required in order to configure the tun1
    network interface and to restart the DHCP server.

11. You should see Bochs start up and attempt to boot from the network,
    with a screen that looks like:

VGA BIOS - Version 2.40
Copyright (C) 1990-2000 Elpin Systems, Inc.
All rights reserved.

Licensed for use with bochs, courtesy of MandrakeSoft.

For information on this or other VGA development products, contact
Elpin Systems at: (800) 723-9038 or www.elpin.com

Bochs BIOS, 1 cpu, $Revision$ $Date$


Etherboot 5.3.6 (GPL) http://etherboot.org Tagged ELF for [PNIC]
Relocating _text from: [00091020,0009fb50) to [01ef14d0,01f00000)
Boot from (N)etwork or (Q)uit?

Probing pci nic...
[pnic] - Detected Bochs Pseudo NIC MAC FE:FD:00:00:00:01 (API v1.0) at 0xdc00
Searching for server (DHCP)...
..Me: 10.254.254.1, Server: 10.254.254.2
Loading 10.254.254.2:/tftpboot/kernel




Serial console
==============

You can use the program "serial-console" to obtain a virtual serial
console for Etherboot running within Bochs.  Simply run
"./serial-console" on a spare tty (e.g. a separate xterm window)
before starting Bochs, and ensure that you have compiled Etherboot
with appropriate settings such as
  CFLAGS+=      -DCONSOLE_DUAL -DCOMCONSOLE=0x3F8 -DCONSPEED=9600

There is a manual page for "serial-console"; use
"man ./serial-console.1" to view it.



TODO
====

Packet forwarding/masquerading - document what must be set up.

Mention possibility of using RFB as the display device - in
conjunction with the serial console, gives you a test facility that
can be accessed remotely.

Mention use of BOCHSBP instruction (xchgw %bx,%bx) to avoid need to
calculate breakpoints.