User interaction options:

-DASK_BOOT=n
		Ask "Boot from Network or from Local? " at startup,
		timeout after n seconds (0 = no timeout); this
		can be done in a more generic way by using the
		IMAGE_MENU, but it requires that the "bootp"
		server is accessible, even when booting locally.
		If unset, boot immediately using the default.
-DANS_DEFAULT=ANS_NETWORK
		Assume Network to previous question
		(alternative: ANS_LOCAL) on timeout or Return key
		See etherboot.h for prompt and answer strings.
-DBAR_PROGRESS
		Use rotating bar instead of sequential dots
		to indicate an IP packet transmitted.
-DMOTD
		Display message of the day; read vendortags.html
		for further information. (Deprecated)
-DIMAGE_MENU
		Allow to interactively chose between different
		bootimages; read vendortags.html for further
		information. (Deprecated)
-DPASSWD
		Enable password protection for boot images; this
		requires -DIMAGE_MENU. (Deprecated)
-DUSRPARMS
		Allow the user to interactively edit parameters
		that are passed to the booted kernel; you should
		probably enable -DPASSWD as well; this feature
		requires -DIMAGE_MENU. (Deprecated)
-DANSIESC
		Evaluate a subset of common ANSI escape sequences
		when displaying the message of the day; this
		probably does not make sense unless you also
		define -DMOTD or at least -DIMAGE_MENU. It is
		possible to combine this option with -DCONSOLE_DUAL,
		but you have to be aware that the boot menu will
		no longer use ANSI escapes to be compatible with the
		serial console. Also be careful with your banners, as
		they may confuse your serial console. Generally you
		lose most of the ANSIESC functionality. (Deprecated)
-DGFX
		Support extensions to the ANSI escape sequences for
		displaying graphics (icons or logos); this
		requires -DANSIESC. It probably does not make sense
		to use -DGFX if you have -DCONSOLE_DUAL, as the
		serial console normally cannot handle the GFX stuff.
		(Deprecated)
-DSHOW_NUMERIC
		Display menu item labels as numbers.
-DDELIMITERLINES
		Print a line of = characters at the start
		and also just before starting an image.
-DSIZEINDICATOR
		Update a running total of the amount of code
		loaded so far, in kilobytes.

Boot autoconfiguration protocol options:

-DNO_DHCP_SUPPORT
		Use BOOTP instead of DHCP.
-DRARP_NOT_BOOTP
		Use RARP instead of BOOTP/DHCP.
-DREQUIRE_VCI_ETHERBOOT
		Require an encapsulated Vendor Class Identifier
		of "Etherboot" in the DHCP reply
		Requires DHCP support.
-DALLOW_ONLY_ENCAPSULATED
		Ignore Etherboot-specific options that are not within
		the Etherboot encapsulated options field.  This option
		should be enabled unless you have a legacy DHCP server
		configuration from the bad old days before the use of
		encapsulated Etherboot options.

Boot tuning parameters:

-DCONGESTED
		Turns on packet retransmission.  Use it on a
		congested network, where the normal operation
		can't boot the image.
-DBACKOFF_LIMIT
		Sets the maximum RFC951 backoff exponent to n.
		Do not set this unreasonably low, because on networks
		with many machines they can saturate the link
		(the delay corresponding to the exponent is a random
		time in the range 0..3.5*2^n seconds).  Use 5 for a
		VERY small network (max. 2 minutes delay), 7 for a
		medium sized network (max. 7.5 minutes delay) or 10
		for a really huge network with many clients, frequent
		congestions (max. 1  hour delay).  On average the
		delay time will be half the maximum value.  If in
		doubt about the consequences, use a larger value.
		Also keep in mind that the number of retransmissions
		is not changed by this setting, so the default of 20
		may no longer be appropriate.  You might need to set
		MAX_ARP_RETRIES, MAX_BOOTP_RETRIES, MAX_TFTP_RETRIES
		and MAX_RPC_RETRIES to a larger value.

Boot device options:

-DCAN_BOOT_DISK
		Can boot from floppy/hd if bootimage matches the
		pattern "/dev/[fhs]d*".
-DTRY_FLOPPY_FIRST
		If > 0, tries that many times to read the boot
		sector from a floppy drive before booting from
		ROM. If successful, does a local boot.
		It assumes the floppy is bootable.
		Requires -DCAN_BOOT_DISK.
-DEMERGENCYDISKBOOT
		If no BOOTP server can be found, then boot from
		local disk. The accessibility of the TFTP server
		has no effect, though! So configure your BOOTP
		server properly. You should probably reduce
		MAX_BOOTP_RETRIES to a small number like 3.

Boot image options:

-DTAGGED_IMAGE
		Add tagged image kernel boot support (Recommended).
-DAOUT_IMAGE
		Add a.out kernel boot support (generic).
-DELF_IMAGE
		Add generic ELF kernel boot support (Recommended).
-DIMAGE_MULTIBOOT
		Add Multiboot image support (currently only
		for ELF images).
		Without this, generic ELF support is selected.
-DIMAGE_FREEBSD
		Add FreeBSD image loading support (requires at least
		-DAOUT_IMAGE and/or -DELF_IMAGE).
-DFREEBSD_KERNEL_ENV
		Pass in FreeBSD kernel environment
-DAOUT_LYNX_KDI
		Add Lynx a.out KDI support

-DDOWNLOAD_PROTO_TFTP
		If defined, boots by TFTP (Recommended).
-DDOWNLOAD_PROTO_NFS
		If defined, boots from a NFS mount and disables
		TFTP loading. Default is DOWNLOAD_PROTO_TFTP
		if neither is defined.

Console options:

-DCONSOLE_CRT
		Set for CRT console (default if nothing else is set).
-DCONSOLE_SERIAL
		Set for serial console.
-DCONSOLE_DUAL
		Set for CRT and serial console, see comment at
		-DANSIESC and -DGFX.
-DCOMCONSOLE
		Set port, e.g. 0x3F8.
-DCONSPEED
		Set speed, e.g. 57600.
-DCOMPARM
		Set Line Control Register value for data bits, stop
		bits and parity. See a National Semiconditor 8250/
		16450/16550 data sheet for bit meanings.
		If undefined, defaults to 0x03 = 8N1.
-DCOMPRESERVE
		Ignore COMSPEED and COMPARAM and instead preserve
		the com port parameters from the previous user
		of the com port.  Examples of previous user are a BIOS
		that implements console redirection, lilo and LinuxBIOS.
		This makes it trivial to keep the serial port
		speed setting in sync between multiple users.
		You set the speed in the first user and the
		rest follow along.

BIOS interface options:

-DPCBIOS
		Compile in support for the normal pcbios
-DLINUXBIOS
		Compile in support for LinuxBIOS

-DBBS_BUT_NOT_PNP_COMPLIANT
		Some BIOSes claim to be PNP but they don't conform
		to the BBS spec which specifies that ES:DI must
		point to the string $PnP on entry. This option
		works around those. This option must be added to
		LCONFIG.
-DNO_DELAYED_INT
		Take control as soon as BIOS detects the ROM.
		Normally hooks onto INT18H or INT19H. Use only if you
		have a very non-conformant BIOS as it bypasses
		BIOS initialisation of devices. This only works for
		legacy ROMs, i.e. PCI_PNP_HEADER not defined.
		This option was formerly called NOINT19H.
-DBOOT_INT18H
		Etherboot normally hooks onto INT19H for legacy ROMs.
		You can choose to hook onto INT18H (BASIC interpreter
		entry point) instead. This entry point is used when
		all boot devices have been exhausted. This option must
		be added to LCONFIG.
-DCONFIG_PCI_DIRECT
		Define this for PCI BIOSes that do not implement
		BIOS32 or not correctly. Normally not needed.
		Only works for BIOSes of a certain era.
-DCONFIG_TSC_CURRTICKS
		Uses the processor time stamp counter instead of reading
		the BIOS time counter.  This allows Etherboot to work
		even without a BIOS.  This only works on late model
		486s and above.
-DPXELOADER_KEEP_UNDI
		For implementation later with UNDI.
-DIBM_L40
		This option uses the 0x92 method of controlling
		A20 instead of the traditional method of using the
		keyboard controller. An explanation of A20 is here:
		http://www.win.tue.nl/~aeb/linux/kbd/A20.html
		This occurs on MCA, EISA and some embedded boards,
		and sometimes with the Fast Gate A20 option on some
		BIOSes.
		Enable this only if you are sure of what you are doing.

Obscure options you probably don't need to touch:

-DPOWERSAVE
		Halt the processor when waiting for keyboard input
		which saves power while waiting for user interaction.
		Good for compute clusters and VMware emulation.
		But may not work for all CPUs.
-DT503_AUI
		Use AUI by default on 3c503 cards.
-DMOVEROM
		If your motherboard does not cache adapter memory
		space, then this option can speed up loading of
		compressed BOOT-Prom images. It has no effect on
		uncompressed images. Unless you are very tight on
		free space, you will usually want to define this
		option.  This option must be added to LCONFIG!
		(Recommended).
-DUSE_LOWMEM_BUFFER
		Define to put some buffers below 0x10000 which
		may interfere with other programs (Deprecated).
