FireWire Port Failures in Host Computers and Peripheral Devices
Monty Solomon
"FireWire Port Failures in Host Computers and Peripheral Devices"
a White Paper
by James Wiebe, CEO
WiebeTech LLC
james...@wiebetech.com
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 Apple's website:
http://discussions.info.apple.com/WebX?1...@103.67TDaKsJjbJ.2@.ef0a4bc
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, WP 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 "bus-powered" storage devices. This is why portable FireWire
drives won't 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.
It's 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 host's 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, let's 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 port's 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:
"Power 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."
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 port's 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
"PHY", and the "PHY", 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 devices' 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 wasn't 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 "spreads" 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 wouldn't 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 computer's 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 WiebeTech's 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 WiebeTech's 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 "soft start" while the device is
still in the off position. This is implemented in WiebeTech's
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 "saved up",
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; it's been done many times.)
* Don't apply twisting torque to cables that are inserted into
sockets.
* If a device doesn't 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
won't 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 host's 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.
Copyright 2003 WiebeTech LLC, All Rights Reserved. FireWire