Transcript Slide 1

USB
• Devices are completely hot-swappable.
Because USB also distributes power,
many USB devices don’t require a
separate power supply
• Although a bus-powered device must be
attached upstream to either a host PC or a
powered hub. Which would require some
power.
• There are four types of USB
connectors: Type A, Type B,
Mini B, and Mini A. USB 1.1
specifies the Type A and
Type B. USB 2.0 specifies
the Type A, Type B, and Mini
B. The Mini A connector was
developed as part of the
USB OTG specification and
is used for smaller
peripherals, such as cell
phones.
USB Speed
• USB 1.1, the original USB standard, has two
data rates: 12 Mbps for devices such as disk
drives that need high-speed throughput and 1.5
Mbps for devices such as joysticks that need
much lower bandwidth.
• The USB protocol is isochronous (allowing
guaranteed realtime performance) and
unidirectional. Blocked channels are
bidirectional and may or may not include error
checking.
USB Networking
• USB uses a tiered hub-and-spoke connection scheme.
The tier starts with a hub, to which a few devices can be
connected. When the top level runs out of connector
space, another hub can be added. A single USB port can
support up to 127 devices.
• USB hubs need to have some intelligence, because they
are required to sense the addition of a device to an
operating bus and inform the host. The hub will not apply
bus power to a device until the host has assigned it an
address, and the bus must recognize high-speed
communication by the host (and not send it out over
unshielded wires or to devices it knows can handle only
the lower speed.)
Data Transmission
• USB relies on the host controller to
manage all transactions.
• USB devices request to the host,
specifying what needs to be done.
• Then the host makes the transfer
descriptor: source node, destination node,
amount of data, read or write, speed, and
the location of the memory buffer.
FireWire
• The IEEE 1394 standard is a fast,
scalable, low-cost digital interface. It was
conceived by Apple® Computer and
developed within the IEEE 1394 Working
Group.
• FireWire is an all-digital interface, there's
no need to convert digital data into analog
for data transmission.
• FireWire normally uses
6-pin, two lines for
power and two twisted
pairs for data
transmission.
• There is also a smaller
4-pin that lacks power
and ground pins.
FireWire Speed
• FireWire supports data rates of 100, 200,
and 400 Mbps, and it supports up to 63
devices with a maximum cable length of
4.5 meters between devices.
• FireWire is a peer-to-peer interface, it
makes it possible to dub from one device
(a digital video camera, for instance) to
another without a computer.
FireWire Application
• By process of negotiation, one device is
selected as the host and bus controller.
• The controller contains: speeds, bus
topology, bus bandwidth, power available
and being consumed, and number of
identities of isochronous channels.
FireWire Networking
• The FireWire protocol is a peer-to-peer
system which has the potential to connect
computers to each other in a high-speed
network.
• Each device is responsible for acquiring
the bus during a portion of the cycle to
transmit its packetized data.
Data Transmission
• Prior to the start of the bus cycle, nodes wishing
to make isochronous transfers query the host.
• At the start of the next bus cycle the channels
are transmitted in order by each host that
requested a channel.
• Then when isochronous data has been
transmitted, and there is a defined gap in data
transmission, the asynchronous data sends out
its packets.
FireWire characteristics
• Hot-pluggable — you don't have to turn off your storage system or
computer to connect or disconnect it, and you don't even need to
restart your computer.
• FireWire-A max raw data rate is 400Mbps (50MB/sec); typical
sustained transfer rate is about 40MB/sec. FireWire-B doubles these
rates.
• Supports up to 63 devices per bus. A typical bus will have between
two and perhaps a dozen devices.
• Hubs are available to provide "tree" layouts in addition to the more
common "daisy-chain".
• Cable lengths can extend up to 14 feet (4.5 meters) between
devices.
• Cables are easy to connect and you don't need device IDs or
terminators.
USB2.0 vs. FireWire
USB 2.0
•
1.5 Mbit/s 12Mbit/s 480Mbit/s supported.
•
USB controller is required to control the bus and data transfer.
•
Cable up to 5 m.
•
Up to 127 devices supported.
•
Power supply to external devices is 500 mA/5V (max).
•
Full compatibility with USB 1.1 devices.
FireWire (IEEE1394)
•
100 Mbit/s 200Mbit/s 400Mbit/s supported.
•
Works without control, devices communicate peer-to-peer.
•
Cable up to 4.5 m.
•
Up to 63 devices supported.
•
Power supply to external devices is 1.25A/12V (max.).
•
The only computer bus used in digital video cameras.
Read Speed
• I was curious about the maximum sustained READ
speed of the FireWire versus USB reader so I ran
ATTO's ExpressPro Tools.
• This shows the maximum realistic throughput of the two
kinds of readers. In this test, the FireWire reader is 5.8
times faster than the USB reader. Hmmm. The FireWire
reader is a lot slower than the fastest FireWire hard
drives (25MB/sec). Maybe the limitation has to do with
the speed of the flash card media itself.
TimeLine
File Copying
Connection
Direct
USB 2.0
FireWire
Business Disk Winmark
6510
4870
6040
Hi-End Winmark
21300
13900
18500
Transfer Begin
41700
12400
27400
Transfer End
25600
12300
25400
CPU usage
17%
15,7%
12%
Access time, ms.
12.5
13.3
12.8