
	Instructions for use of the 3C90X driver for EtherBoot

		Original 3C905B support by:
			Greg Beeley (Greg.Beeley@LightSys.org),
			LightSys Technology Services, Inc.
			February 11, 1999

		Updates for 3C90X family by:
			Steve Smith (steve.smith@juno.com)
			October 1, 1999

		Minor documentation updates by
			Greg Beeley (Greg.Beeley@LightSys.org)
			March 29, 2000

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I   OVERVIEW

    The 3c90X series ethernet cards are a group of high-performance busmaster
    DMA cards from 3Com.  This particular driver supports both the 3c90x and
    the 3c90xB revision cards.  3C90xC family support has been tested to some
    degree but not extensively.

    Here's the licensing information:

    This program Copyright (C) 1999 LightSys Technology Services, Inc.
    Portions Copyright (C) 1999 Steve Smith.

    This program may be re-distributed in source or binary form, modified,
    sold, or copied for any purpose, provided that the above copyright message
    and this text are included with all source copies or derivative works, and
    provided that the above copyright message and this text are included in the
    documentation of any binary-only distributions.  This program is
    distributed WITHOUT ANY WARRANTY, without even the warranty of FITNESS FOR
    A PARTICULAR PURPOSE or MERCHANTABILITY.  Please read the associated
    documentation "3c90x.txt" before compiling and using this driver.


II  FLASH PROMS

    The 3c90xB cards, according to the 3Com documentation, only accept the
    following flash memory chips:

	Atmel AT29C512 (64 kilobyte)
	Atmel AT29C010 (128 kilobyte)

    The 3c90x cards, according to the 3Com documentation, accept the
    following flash memory chips capacities:

	64  kb (8 kB)
	128 kb (16 kB)
	256 kb (32 kB) and
	512 kb (64 kB)

    Atmel AT29C512 (64 kilobyte) chips are specifically listed for both
    adapters, but flashing on the 3c905b cards would only be supported
    through the Atmel parts.  Any device, of the supported size, should
    be supported when programmed by a dedicated PROM programmer (e.g.
    not the card).

    To use this driver in such a PROM, visit Atmel's web site and download
    their .PDF file containing a list of their distributors.  Contact the
    distributors for pricing information.  The prices are quite reasonable
    (about $3 US each for the 64 kB part), and are comparable to what one would
    expect for similarly sized standard EPROMs.  And, the flash chips are much
    easier to work with, as they don't need to be UV-erased to be reprogrammed.
    The 3C905B card actually provides a method to program the flash memory
    while it is resident on board the card itself; if someone would like to
    write a small DOS program to do the programming, I can provide the
    information about the registers and so forth.

    A utility program, 3c90xutil, is provided with Etherboot in the 'contrib'
    directory that allows for the on-board flashing of the ROM while Linux
    is running.  The program has been successfully used under Linux, but I
    have heard problem reports of its use under FreeBSD.  Anyone willing to
    make it work under FreeBSD is more than welcome to do so!

    You also have the option of using EPROM chips - the 3C905B-TX-NM has been
    successfully tested with 27C256 (32kB) and 27C512 (64kB) chips with a
    specified access time of 100ns and faster.


III GENERAL USE

    Normally, the basic procedure for using this driver is as follows:

	1.  Run the 3c90xcfg program on the driver diskette to enable the
	boot PROM and set it to 64k or 128k, as appropriate.
	2.  Build the appropriate 3c90x.fd0 or 3c90x.fd0 floppy image with
	possibly the value CFG_3C90X_XCVR defined to the transceiver type that
	you want to use (i.e., 10/100 rj45, AUI, coax, MII).
	3.  Run the floppy image on the PC to be network booted, to get
	it configured, and to verify that it will boot properly.
	4.  Build the 3c90x.rom or 3c90x.lzrom PROM image and program
	it into the flash or EPROM memory chip.
	5.  Put the PROM in the ethernet card, boot and enable 'boot from
	network first' in the system BIOS, save and reboot.

    Here are some issues to be aware of:

	1.  If you experience crashes or different behaviour when using the
	boot PROM, add the setting CFG_3C90X_BOOTROM_FIX and go through the
	steps 2-5 above.  This works around a bug in some 3c905B cards (see
	below), but has some side-effects which may not be desirable.
        Please note that you have to boot off a floppy (not PROM!) once for
        this fix to take effect.
	2.  The possible need to manually set the CFG_3C90X_XCVR value to
	configure the transceiver type.  Values are listed below.
	3.  The possible need to define CFG_3C90X_PRESERVE_XCVR for use in
	operating systems that don't intelligently determine the
	transceiver type.

    Some things that are on the 'To-Do' list, perhaps for me, but perhaps
    for any other volunteers out there:

	1.  Extend the driver to fully implement the auto-select
	algorithm if the card has multiple media ports.
	2.  Fix any bugs in the code <grin>....
	3.  Extend the driver to support the 3c905c revision cards
	"officially".  Right now, the support has been primarily empirical
	and not based on 3c905C documentation.

    Now for the details....

    This driver has been tested on roughly 300 systems.  The main two
    configuration issues to contend with are:

	1.  Ensure that PCI Busmastering is enabled for the adapter (configured
	in the CMOS setup)
	2.  Some systems don't work properly with the adapter when plug and
	play OS is enabled; I always set it to "No" or "Disabled" -- this makes
	it easier and really doesn't adversely affect anything.

    Roughly 95% of the systems worked when configured properly.  A few
    have issues with booting locally once the boot PROM has been installed
    (this number has been less than 2%).  Other configuration issues that
    to check:

	1.  Newer BIOS's actually work correctly with the network boot order.
	Set the network adapter first.  Most older BIOS's automatically go to
	the network boot PROM first.
	2.  For systems where the adapter was already installed and is just
	having the PROM installed, try setting the "reset configuration data"
	to yes in the CMOS setup if the BIOS isn't seen at first.  If your BIOS
	doesn't have this option, remove the card, start the system, shut down,
	install the card and restart (or switch to a different PCI slot).
	3.  Make sure the CMOS security settings aren't preventing a boot.

    The 3c905B cards have a significant 'bug' that relates to the flash prom:
    unless the card is set internally to the MII transceiver, it will only
    read the first 8k of the PROM image.  Don't ask why -- it seems really
    obscure, but it has to do with the way they mux'd the address lines
    from the PCI bus to the ROM.  Unfortunately, most of us are not using
    MII transceivers, and even the .lzrom image ends up being just a little
    bit larger than 8k.  Note that the workaround for this is disabled by
    default, because the Windows NT 4.0 driver does not like it (no packets
    are transmitted).

    So, the solution that I've used is to internally set the card's nvram
    configuration to use MII when it boots.  The 3c905b driver does this
    automatically.  This way, the 16k prom image can be loaded into memory,
    and then the 3c905b driver can set the temporary configuration of the
    card to an appropriate value, either configurable by the user or chosen
    by the driver.

    To enable the 3c905B bugfix, which is necessary for these cards when 
    booting from the Flash ROM, define -DCFG_3C90X_BOOTROM_FIX when building,
    create a floppy image and boot it once.
    Thereafter, the card should accept the larger prom image.

    The driver should choose an appropriate transceiver on the card.  However,
    if it doesn't on your card or if you need to, for instance, set your
    card to 10mbps when connected to an unmanaged 10/100 hub, you can specify
    which transceiver you want to use.  To do this, build the 3c905b.fd0
    image with -DCFG_3C90X_XCVR=x, where 'x' is one of the following
    values:

	0	10Base-T
	1	10mbps AUI
	3	10Base-2 (thinnet/coax)
	4	100Base-TX
	5	100Base-FX
	6	MII
	8	Auto-negotiation 10Base-T / 100Base-TX (usually the default)
	9	MII External MAC Mode
	255	Allow driver to choose an 'appropriate' media port.

    Then proceed from step 2 in the above 'general use' instructions.  The
    .rom image can be built with CFG_3C90X_XCVR set to a value, but you
    normally don't want to do this, since it is easier to change the
    transceiver type by rebuilding a new floppy, changing the BIOS to floppy
    boot, booting, and then changing the BIOS back to network boot.  If
    CFG_3C90X_XCVR is not set in a particular build, it just uses the
    current configuration (either its 'best guess' or whatever the stored
    CFG_3C90X_XCVR value was from the last time it was set).

    [[ Note for the more technically inclined:  The CFG_3C90X_XCVR value is
    programmed into a register in the card's NVRAM that was reserved for
    LanWorks PROM images to use.  When the driver boots, the card comes
    up in MII mode, and the driver checks the LanWorks register to find
    out if the user specified a transceiver type.  If it finds that
    information, it uses that, otherwise it picks a transceiver that the
    card has based on the 3c905b's MediaOptions register.  This driver isn't
    quite smart enough to always determine which media port is actually
    _connected_; maybe someone else would like to take on that task (it
    actually involves sending a self-directed packet and seeing if it
    comes back.  IF it does, that port is connected). ]]

    Another issue to keep in mind is that it is possible that some OS'es
    might not be happy with the way I've handled the PROM-image hack with
    setting MII mode on bootup.  Linux 2.0.35 does not have this problem.
    Behavior of other systems may vary.  The 3com documentation specifically
    says that, at least with the card that I have, the device driver in the
    OS should auto-select the media port, so other drivers should work fine
    with this 'hack'.  However, if yours doesn't seem to, you can try defining
    CFG_3C90X_PRESERVE_XCVR when building to cause Etherboot to keep the
    working setting (that allowed the bootp/tftp process) across the eth_reset
    operation.


IV  FOR DEVELOPERS....

    If you would like to fix/extend/etc. this driver, feel free to do so; just
    be sure you can test the modified version on the 3c905B-TX cards that the
    driver was originally designed for.  This section of this document gives
    some information that might be relevant to a programmer.

    A.  Main Entry Point

	a3c90x_probe is the main entry point for this driver.  It is referred
	to in an array in 'config.c'.

    B.  Other Important Functions

	The functions a3c90x_transmit, a3c90x_poll, a3c90x_reset, and
	a3c90x_disable are static functions that EtherBoot finds out about
	as a  result of a3c90x_probe setting entries in the nic structure
	for them.  The EtherBoot framework does not use interrupts.  It is
	polled.  All transmit and receive operations are initiated by the
	etherboot framework, not by an interrupt or by the driver.

    C.  Internal Functions

	The following functions are internal to the driver:

	a3c90x_internal_IssueCommand - sends a command to the 3c905b card.
	a3c90x_internal_SetWindow - shifts between one of eight register
	windows onboard the 3c90x.  The bottom 16 bytes of the card's
	I/O space are multiplexed among 128 bytes, only 16 of which are
	visible at any one time.  This SetWindow function selects one of
	the eight sets.
	a3c90x_internal_ReadEeprom - reads a word (16 bits) from the
	card's onboard nvram.  This is NOT the BIOS boot rom.  This is
	where the card stores such things as its hardware address.
	a3c90x_internal_WriteEeprom - writes a word (16 bits) to the
	card's nvram, and recomputes the eeprom checksum.
	a3c90x_internal_WriteEepromWord - writes a word (16 bits) to the
	card's nvram.  Used by the above routine.
	a3c90x_internal_WriteEepromWord - writes a word (16 bits) to the
	card's nvram.  Used by the above routine.

    D.  Globals

	All global variables are inside a global structure named INF_3C90X.
	So, wherever you see that structure referenced, you know the variable
	is a global.  Just keeps things a little neater.

    E.  Enumerations

	There are quite a few enumerated type definitions for registers and
	so forth, many for registers that I didn't even touch in the driver.
	Register types start with 'reg', window numbers (for SetWindow)
	start with 'win', and commands (for IssueCommand) start with 'cmd'.
	Register offsets also include an indication in the name as to the
	size of the register (_b = byte, _w = word, _l = long), and which
	window the register is in, if it is windowed (0-7).

    F.  Why the 'a3c90x' name?

	I had to come up with a letter at the beginning of all of the
	identifiers, since 3com so conveniently had their name start with a
	number.  Another driver used 't' (for 'three'?); I chose 'a' for
	no reason at all.

Addendum by Jorge L. deLyra <delyra@latt.if.usp.br>, 22Nov2000 re
working around the 3C905 hardware bug mentioned above:

Use this floppy to fix any 3COM model 3C905B PCI 10/100 Ethernet cards
that fail to load and run the boot program the first time around. If
they have a "Lucent" rather than a "Broadcom" chipset these cards have
a configuration bug that causes a hang when trying to load the boot
program from the PROM, if you try to use them right out of the box.

The boot program in this floppy is the file named 3c905b-tpo100.rom
from Etherboot version 4.6.10, compiled with the bugfix parameter

			CFG_3C90X_BOOTROM_FIX

You have to take the chip off the card and boot the system once using
this floppy. Once loaded from the floppy, the boot program will access
the card and change some setting in it, correcting the problem. After
that you may use either this boot program or the normal one, compiled
without this bugfix parameter, to boot the machine from the PROM chip.

[Any recent Etherboot version should do, not just 4.6.10 - Ed.]