this is a copy in its entirity from what M-Audio sent me about firewire
failures

³FireWire Port Failures in Host Computers and Peripheral Devices²

*

a White Paper

*

by James Wiebe, CEO

WiebeTech LLC



http://www.wiebetech.com

© 2003 All Rights Reserved

*

This paper may be reproduced, but only in its entirety, and only if credit is
given to the author and linkage provided to the WiebeTech website.

*

DISCLAIMER

*

The cause of FireWire port failures is extremely complex and this White Paper
cannot embody all possible failure scenarios or solutions to the problems.*
The author specifically disclaims any fitness for use of the information
contained within this white paper.*

*

Port failures are often discussed but remain a relatively infrequent problem,
especially if the FireWire storage device and the host computer are properly
designed.*

*

Statistics for total failures of FireWire ports is not known.* Judging from
the number of posts on Apple¹s website:

*

http://discussions.info.apple.com/[email protected]

*

as well as posts on the website:

*

http://www.macintouch.com/firewirereader02.html

*

this topic is assumed to be of interest to many readers.

*

The author seeks input from anyone who may have additional information which
can shed light on the subject of this White Paper.* Questions concerning
particular types of equipment should be directed to the respective
manufacturer.

*

1.******** INTRODUCTION

*

FireWire allows users to connect storage devices and other peripherals to
host computers, giving unparalled flexibility in data capture, storage,
transportation, and backup capabilities.* FireWire allows devices to be hot
swapped from one computer to another.* Hot swapping allows FireWire storage
devices (as well as other peripherals, such as video cameras) to be
physically attached to a FireWire port, automatically mounted on the desktop,
accessed, and then unmounted / disconnected at the command of the user.

*

The resulting ease of use has caused FireWire technology to be widely
accepted by millions of users.* FireWire is directly supported by a variety
of operating systems, including Windows 98SE, ME, 2K, XP and Mac OS9.1, 9.2
and OSX.* Linux also is capable of supporting FireWire, although the process
of setting up first use on that platform may be a little more difficult.*

*

Users have reported failures of FireWire ports on host computers after
attaching FireWire devices to those ports.* This can be quite unsettling to
the user, since the failure of the FireWire port can be crippling to the
utilization of the computer.* For instance, it may become impossible to
create backups or attach FireWire peripherals to the computer after failure
of the port.

*

The purpose of this report is to provide background and technical analysis of
the failure of the ports.* In conclusion, methodologies will be suggested
which may substantially reduce the incidence of damage to host ports.

*

2.******** BACKGROUND INFORMATION ON FIREWIRE OPERATION

*

In order to understand the issue, it is necessary to understand just a little
bit of how FireWire operates.

*

FireWire allows the attachment of external devices to host computers through
a cable which is composed of the following wiring components:

*
€ Serial Data Pairs, of which there are two, giving a total of 4 wires.
€ Power, which is generally somewhere between 8 to 24 volts DC.
€ Ground, which is a lead that provides a current return for the Power
line.
€ Shield, which helps prevent the emission of Radio Frequency
Interference from the FireWire cable.

*

The Power and Ground lines must be present to allow FireWire devices to be
bus powered.* For instance, portable FireWire drives usually run off of bus
power, meaning that they will function when attached to a powered FireWire
host.* Other types of FireWire devices, such as Desktop FireWire drives,
usually (but not always) require a separate power supply.* As a result, they
do not utilize any power from the Power / Ground pair provided by the host
FireWire port.* They obtain their power from an independent power supply.

*

Manufacturers are not required to provide Power and Ground within the
FireWire host.* Two different types of commonly used FireWire connectors have
been defined for FireWire 400 usage.* One of these types is the more common
six pin connector, while the other type is a physically smaller connector
which omits Power and Ground.* Obviously, bus powered FireWire devices will
not work when attached to a FireWire host which does not provide bus power.*

*

Apple computers generally include all of these lines in their FireWire ports,
while certain PC computers with FireWire capability (such as the Inspiron
8200 from Dell or various Sony Vaio laptops) omit the Power and Ground
lines.* The omission of these lines prevents the use of ³bus-powered² storage
devices.* This is why portable FireWire drives won¹t work when attached
directly to PC laptop computers, such as the Dell or Sony models.* No power
is present on the port.

*

3.******** FIREWIRE FAILURE SCENARIO

*

A typical failure scenario is as follows:* The user attaches a FireWire
storage device to the computer.* The user expects the device to mount on the
desktop, but this does not occur.* Repeated attempts to mount the storage
device (usually by connecting and disconnecting the FireWire cable) produce
the same results.* Ultimately, the user attempts to mount other FireWire
devices on the same port without success, and consequently verifies that the
port is no longer functional.* Various attempts to resolve the situation may
be attempted, all without success.* This may include machine rebooting,
Parameter RAM resetting, power disconnection for extended periods of time,
etc.

*

It¹s worth noting that the host FireWire port may be on the motherboard (as
is the case for most Apple computers) or it may be on a PCI FireWire host
adapter card.* The result is the same; the particular port no longer works.*
The port may still be capable of supplying power to the attached FireWire
device, but the device is no longer seen on the desktop or in the various
disk management utilities.

*

The failure of the host¹s FireWire port can produce a very bad day for the
user.* The knowledge of possible damage (and consequential repair cost /
hassle) to the computer is compounded by the frustrating inability to mount
and use external storage devices.

*

4.******** FAILURE CAUSES

*

4.1****** LOSS OF POWER FROM THE PORT

*

What went wrong to cause the failure of the FireWire port?

*

In order to answer the question, let¹s consider the two main functional
components of the FireWire interface:* the Data lines and the Power lines.* A
failure mode is the loss of Power through the FireWire port.* A second
failure mode (which the author believes to be far more likely) is a failure
of the port¹s ability to supply Data to the FireWire device.*

*

These failure modes cause us to consider:* why would a port lose the ability
to supply either Power or Data?*

*

In the testing and development of FireWire storage devices, we (WiebeTech)
have accidentally shorted the FireWire Power / ground lines together many
times.* This can cause a variety of results:* the immediate shutdown of the
entire computer system; the shutdown of an individual port; etc.* Apple
documents that their ports are provided with triple redundant fusing for
protection against power shorts such as the one just described.* The
applicable document can be accessed at the following URL, showing FireWire
specifications on all Apple computers:

*

http://docs.info.apple.com/article.html?artnum=58207

*

The Apple document states:

*

³Power safety -- The FireWire bus has three self-resetting fuses. If your
device unexpectedly shuts down, it may be due to an overloaded fuse. If this
occurs, disconnect the device immediately.²

*

Field experience shows that the power side of the FireWire host port rarely
fails.* Fuse protection appears to adequately protect the port against most
problems.

*

4.2****** LOSS OF DATA TRANSMISSION FROM THE PORT

*

The second failure mode is the failure of the port¹s ability to supply Data
to the FireWire device.* As previously stated, the author believes this to be
the most common failure mode when FireWire ports fail.

*

FireWire ports within most peripherals are composed of two devices:* the
FireWire bridge, which connects to the drive and to the FireWire ³PHY², and
the ³PHY², which connects from the FireWire cable to the FireWire bridge.*
The PHY receives nearly no mention in most discussion of FireWire devices,
but it is actually responsible for the electrical connection to the FireWire
cable, and ultimately, the host device.* The host devices¹ FireWire
connection is very similar, using a PHY to connect the motherboard
electronics to the FireWire port.

*

The author has direct experience observing the failure of FireWire ports in
peripheral devices under developmental test conditions.* This experience
shows that most port failures occur within the PHY, not in the FireWire
bridge, and not in the power supply portion of the port.*

*

Post mortem examination of the decapped (plastic removed) failed PHY shows
gross failure of the circuitry which attaches the Data lines.* After removing
the plastic package from the integrated circuit, an examination of the
integrated circuit under a microscope shows clear evidence of electrical
damage to the part.

*

In other words, something zapped the PHY.* How is this possible?

*

It really wasn¹t supposed to be possible for the PHY to fail.* However, there
are at many different events which can cause the PHY to fail.* Some of these
are very easy to understand, while others are a bit more difficult to
understand.

*

4.2.1*** FAILURE BY ELECTROSTATIC DISCHARGE (ESD)

*

The failure scenario is as follows:* The user inserts a FireWire cable into
the host.* The user then picks up the other end to attach to the FireWire
device, and inadvertently discharges ESD through one of the Data lines to the
host port.* Part destruction occurs.

*

In the real world, this does not (or at least should not) happen frequently.*
The user is far more likely to discharge through the Shield of the FireWire
cable, which will dissipate the discharge directly to a ground within the
host computer, without damaging internal circuitry.*

*

4.2.2*** PORT FAILURE BY BAD CABLE OR BAD INSERTION

*

This failure scenario actually has three sub-scenarios, each of which will be
described in turn.

*

4.2.2.1 PORT FAILURE BY REVERSE INSERTION

*

In this scenario, the user inserts the cable with the connector twisted 180
degrees.* An examination of the FireWire six pin ports suggests that this is
not possible, but it has actually been done many times.* It is more likely to
happen when the port is worn, or when the port easily ³spreads² when reverse
inserted.* Some FireWire ports are built with the metal seam at the narrow
end of the port, making it much easier to reverse insert the cable.* The
resulting (errant) electrical connections cause Power lines to be directly
connected to Data lines.* This invariably fries the PHY attached to that
port.

*

4.2.2.2 PORT FAILURE BY BAD CABLE

*

Any internal failure of a FireWire cable which results in Power being shorted
to a Data line within the cable usually will result in the failure of the
port to which it is attached.

*

The author was directly told of a typical experience at a major computer
company.* An employee observed that his FireWire drive would not mount.*
Suspecting trouble and wanting to verify it, the employee tested the device
on three more computers.* The device wouldn¹t mount on any of the four
computers.* The ultimate cause of the problem was a bad cable which fried
four host ports on the four computers.* The FireWire drive was not at fault.*
The author assumes that each of the four PHYs was destroyed.

*

4.2.2.3 PORT FAILURE BY FIREWIRE CABLE TWISTING

*

In this scenario, the user correctly attaches the FireWire cable to the
computer and the storage device.* A rotational twisting force is applied to
either connector at either end of the cable, in relationship to the port in
which it is inserted.* As the connectors are pushed out of position by the
rotational torque, a short occurs between the Data lines and a Power line,
resulting in port failure.*

*

4.2.3*** PORT FAILURE BY INDUCED UNDER/OVER VOLTAGE CONDITION

*

This is the scenario which is most difficult to understand.* Essentially, the
PHY creates or experiences a damaging voltage on one of the Data lines.* This
error condition is very transient in nature and is caused at startup time of
bus powered FireWire devices by a bump or droop on a power supply within the
FireWire device.* The bump or droop is understood through a detailed analysis
of the actual circuit of the FireWire device, cable, and host port as current
starts to flow through the Power lines at startup time.* Equivalent circuitry
must be considered:* IE, inductance within power lines, etc.* (The
engineering analysis is far beyond the scope of this paper.)

*

As a result, the external FireWire device may briefly experience or transmit
a damaging voltage to the host computer¹s FireWire port, resulting in the
destruction of the port.**

*

This failure mode is the one most likely to have created the impression that
bus powered devices cause FireWire host port failures.

*

5.******** PREVENTING FIREWIRE PORT FAILURE

*

5.1************* OBVIOUS PREVENTATIVES

*

Certain preventive measures seem obvious:

*
€ Always use high quality FireWire cables.
€ If a cable is worn out, replace it immediately.* (Cables used at
WiebeTech are used heavily throughout every business day; they are
generally replaced every month, if not more frequently.)
€ Never insert a cable backwards into a port.* If this happens before
the cable is also attached to the host (or to the peripheral device), get
the port repaired prior to further use of the device (or host).* Discard
the cable and use a new one.
€ If a device does not mount, attempt mounting it with a new cable on
the same port.* Always suspect the cable before suspecting a failure of
the device.* Try powering the host down; rebooting; etc.* Port failures on
machines tend to follow the cable.

*

5.2************* PREVENTING PORT FAILURE WHEN USING BUS POWERED DEVICES

*

What follows is three different methods for preventing port failure when
using bus powered devices.* All require support from the FireWire peripheral
manufacture and from the host computer.* Other methods are also available *
this is not meant to be an exhaustive list.

*

5.2.1******* ESD AND OVER/UNDER VOLTAGE

*

This technique requires installation of protective devices on the FireWire
port on the host computer.* The protection is installed on the motherboard
close to the PHY device, with direct connections to the Data lines.* An
excellent example of how Apple has implemented this technique in certain
reworked motherboards is found at the following URL:

*

http://www.medicalmac.com/mac98e.html

*

Through proper implementation of this technique, the FireWire port is
protected against Electro Static Discharge (ESD) as well as problems caused
by bus powered devices.*

*

The author believes that Apple has been implementing the technique in all
recent and currently shipping Apple computers.* Suppression of ESD and
over/under voltage is a primary method of reducing or eliminating port
failure and must be implemented on the host computer to be effective.

*

5.2.2*** VOLTAGE TRANSIENT SUPPRESSION CIRCUITRY ON BUS POWERED DEVICES

*

WiebeTech has implemented a proprietary technique which prevents transients
at power on time from being transmitted to the host computer via the Data
lines.* This resolves issues related to use of bus powered devices.* This
technique has been used with excellent results in WiebeTech¹s bus powered
FireWire DriveDock devices, which are capable of bus powering 3.5 inch IDE
hard drives.*

*

5.2.3******* THE USE OF A POWER SWITCH IN BUS POWERED DEVICES.

*

WiebeTech recommends the use of power switches in bus powered FireWire
devices.* This prevents the PHY within the FireWire device from transmitting
voltage transients through the FireWire cable to the PHY on the motherboard
of the host computer.* Simply put, the FireWire device is not powered up
until all connections have been made and voltages have had a chance to
stabilize.* This technique is used on WiebeTech¹s portable drives, including
the MicroGB+; MicroGB+Combo; and 3.5 inch bus powered UltraGB.

*

5.2.4******* CURRENT LIMITING OF POWER ON TRANSIENTS

*

WiebeTech has also implemented a technique which allows the power supply of
the FireWire device to ³soft start² while the device is still in the off
position.* This is implemented in WiebeTech¹s UltraGB 3.5 inch bus powered
drive.* The UltraGB has a three position switch:* Bus Power * Off *AC Power.*
When the Off position is selected AND when the device is attached to a host
through a FireWire cable, the internal power supply ramps up to voltage
through a current limiting circuit into a power storage circuit.* This
provides important benefits:* a substantial amount of power may be ³saved
up², helping large drives to spin up successfully; and power on transients
are filtered through the current limiter, substantially reducing bumps and
droops in the power supply.

*

5.3****** OTHER METHODS OF RESOLVING HOST PORT FAILURES

*

5.3.1******* REPAIR THE MACHINE

If the user has a computer under warranty, it is likely that the manufacturer
will repair the damaged port without charge of any kind.* It may be
worthwhile checking with the manufacturer, even if the computer is out of
warranty.

*

5.3.2*** ADD AN INEXPENSIVE FIREWIRE HOST CARD

*

If the machine is out of warranty and has available PCI slots, the simplest
way to repair the computer is to add a FireWire PCI card.* They are
inexpensive and very easy to install.* Most operating systems do not require
the installation of any additional software drives to support FireWire usage
through a PCI card.

*

6.***************** CONCLUSIONS

*

Most of the failure modes of FireWire ports are believed to be caused by low
quality or worn out FireWire cables, operator error during device and cable
insertion, inadequate PHY port protection, and improper design of external
FireWire devices which causes voltage surges to the host port.

*

6.1****** CABLE PREVENTATIVES

*
€ Users are encouraged to use high quality FireWire cables.
€ Users are encouraged to replace worn out FireWire cables.
€ Never plug a FireWire cable in backwards (although it seems
impossible; it¹s been done many times.)
€ Don¹t apply twisting torque to cables that are inserted into sockets.
€ If a device doesn¹t mount, do not test the cable on another machine.

*

6.2************* HOST PORTS

*
€ Older computers may not have FireWire port protection built into
them.* This appears to place them at higher risk of failure.
€ Recently manufactured computers are likely to have enhanced port
protection.
€ If your port fails while the computer is within warranty, you won¹t
have any problems getting it repaired.
€ If your port fails while the computer is out of warranty, an
inexpensive solution is to use a low cost PCI FireWire host card.**
(assuming you have open slots).

*

6.3****** FIREWIRE PERIPHERALS

*
€ FireWire Peripherals should have a transient limiting circuitry on the
Data lines at power up time, in order to prevent transients from causing
damage to the host¹s PHY.
€ An alternative method is to use FireWire devices that are turned on
via switch after attachment to the FireWire cable.
€ Another method is to use FireWire peripherals with built in inrush
current limiting on the Power lines.
€ Always follow the attachment and power up recommendations of your
host and peripheral manufacturer!

*

The author hopes this material has been helpful in shedding light on the
issue of FireWire port failures.

*

© 2003 WiebeTech LLC, All Rights Reserved.* FireWire

*

*

*
Thank you to those who made this available
George