USB Fundamentals and Applications for Digital Signal Processing

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USB Fundamentals and Applications for Digital Signal Processing

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Title: USB Fundamentals and Applications for Digital Signal Processing

1
USB Fundamentals and Applications for Digital
Signal Processing

Greg Burk
J. Gordon Electronic Design
burk_at_jged.com
7/30/2004

2
Agenda

USB Specifications
USB Basics
Components
Onion introduction
Signaling
Packets
Transfers
Requests
Operating System Interface
Considerations for DSP Applications
USB Resources

3
USB Specifications

USB 1.0 The original spec, superseded quickly
by USB 1.1
USB 1.1 Minor enhancements to the USB 1.0 spec,
supported Low and Full speed devices
USB 2.0 The Current Standard, added high
speed to USB 1.1
USB OTG USB On-the-Go, a supplement to the USB
2.0 spec that added a form of device to device
communications.
WUSB Wireless USB, a work in progress -- not a
standard yet

4
USB Founding Companies
USB 1.0 USB 2.0
Compaq Compaq
Intel Intel
Microsoft Microsoft
NEC NEC
IBM Lucent
DEC HP
Northern Telecom Philips
5
USB 2.0 in a Nutshell

Runs 40X faster than USB 1.1
Low speed 1.5Mb/s
Full speed 12Mb/s
High speed 480Mb/s
Fully supports existing USB devices
Forward compatibleplug existing 1.1 devices into
new 2.0 hosts
Backward compatibleplug new 2.0 devices into
existing 1.1 hosts
Uses the same cables as USB 1.1

6
USB On-the-Go (USB OTG)

Connect two peripherals together
PC is not required (but still supported)
Allow peripherals to wake up hosts
Allow two devices to exchange the host role
New OTG devices can tap into the existing 900
million USB devices

7
USB OTG Example ApplicationsSource Beeman
www.usbonthego.com
8
USB OTG Details

Defines a new connector and cable
Mini AB receptacle
Mini-A to Mini-B cable
Cable establishes the default host
A-Device is the default host
Dual-role USB devices
Are sometimes a peripheral, sometimes a host
Must use the new AB connector
Provide limited host capability
Targeted peripheral list
Operate at full speed (high speed optional)

9
Wireless USB (WUSB)

Specification currently under development
(expected release early 2005)
Key players are Intel, Microsoft, HP, NEC,
Phillips Semiconductors, Agere Systems, and
Samsung Electronics
Based on Ultra-wideband (UWB) standard
Supposed to support USB 2.0 bandwidth (480 Mb/s)
at distances of up to 10 meters
Projected Feature Set
Compatibility with USB 2.0 Standard
Security at same level as wired USB
Connections up to 127 WUSB device
For More info see http//www.intel.com/labs/wusb/
(This is NOT the same as Cypress Semiconductors
Wireless USB)

10
USB Basics
11
USB Basics

USB is a Master/Slave Polled Bus (PC is the
Master, Devices are the Slaves)
USB has a tiered star architecture that can USB
can support up to 126 devices
7-bit address 128 root hub reserved addr 0
for enumeration
USB is Hot Pluggable
USB connections can provide both data and power
to the devices

12
USB is not Simple

Outside, it is simple
The rich user experience requires some inner
complexity
Even though it replaces serial and parallel
ports, its not a drop-in replacement
Its electrically simple, but a whole protocol
layer is added

13
USB Projects Can Require a Significant Code
Development Effort

Device side
USB houskeeping firmware
Application firmware
Host side
Driver (maybe)
Application software

14
USB Components
15
Components of USB Systems

USB Host Controllers
USB Hubs
USB Cables
USB Peripheral Devices

16
USB Host Controllers

Reside in PC on motherboard or add-in card
Are the master device on the USB bus
Host Controller has integral Root Hub
Host Controller Interfaces
Universal Host Controller Interface (UHCI)
Open Host Controller Interface (OHCI)
Enhanced Host Controller Interface (EHCI)

17
USB Cables

Transport both Data and Power
Four wires Vbus, GND, D, D
Cables are 5 meters MAX
Two connector types, A and B
Prevents illegal topologies
A connectors are the ones that goes to the PC
or Hub, B connectors goes to the device) (OTG
adds Miny A and Mini B connectors)
Cables can be either captive (like mice) or
detachable
Cables can be unshielded (Low speed devices) or
shielded (Full Speed and High Speed devices)
USB extension cables are ILLEGAL

18
USB Hubs

A hub provides additional connection points
(ports) for devices
Hubs can be
Self-Powered (lt 500ma to each device)
Bus-Powered (lt 100mA to each device)
Hubs contain most of the magic and differences
between USB 1.1 and USB 2.0

19
USB Devices

Devices can be
Self-Powered
External Power Source (i.e. wall wart)
Batteries
Bus-Powered
Low Power Bus Powered (lt 100mA)
High Power Bus Powered gt100mA, lt500mA)
Devices are self describing
Devices return data (USB descriptors) to host to
indicate its capabilities, configurations, and
how the device is able to communicate

20
Compound and Composite Devices

Composite Device
Multiple interfaces, independently controlled
Each interface can have a different driver
Compound Device
Collection of separate functions, each with a USB
address, connected to an internal hub
Example Keyboard Trackball in same package

21
USB is a Polled BUS

The Host (PC) initiates all transfers
Devices respond to host requests
Direction OUT is host-to-device
Direction IN is device-to-host
USB is NOT peer-to-peer (not even in USB OTG)

22
USB Topology
PC
PC
USB
USB
USB
USB
Hub
Device
Device
Device
USB
USB
USB
USB
Device
Device
Tiered Star
23
USB Transfer Speeds

USB 1.1
Low speed is 1.5Mb/s
Full speed is 12Mb/s
USB 2.0
Low speed is 1.5Mb/s
Full speed is 12Mb/s
High speed is 480 Mb/s
There is a VERY common misconception that say a
device is USB 2.0 compliant that it means that it
is High Speed device. It does NOT!

24
Endpoints

USB Spec a source or sink of data
A Control Transfer Type endpoint is
bi-directional
Others are uni-directional
Four address bits plus a direction bit selects
between up to 32 buffers (FIFOs)
Different USB chips support
Various numbers of endpoints
Various buffer sizes
Each device must have 1 Control Type Endpoint
(Commonly referred to as Endpoint 0 or the
Default Endpoint)

25
Pipes

An abstraction used by the USB spec used to
indicate that 2 endpoints are joined (one in the
PC Host and the other in the device).
CONTROL pipe is bi-directional
Others are uni-directional

26
USB Descriptors

Device Descriptors
Contains the VID/PID/DID/Serial Number
Configuration Descriptors
Interface Descriptors
Endpoint Descriptors
String Descriptors
Device Qualifier Descriptors (USB 2.0)
Other Speed Configuration Descriptors (USB 2.0)
USB Classes can add other class specific
Descriptors

27
The USB Onion
28
Signaling
29
USB Signaling

USB utilizes differential signaling on the D and
D- lines.
Data is encoded in non-return to zero with bit
stuffing
Bit stuffing is used to ensure enough transitions
for the clock recovery circuitry.
Most designs use silicon that incorporates an
integral Serial Interface Engine (SIE) so you
dont have to worry about the decoding yourself.
PCB layout of D and D- requires care (especially
on High Speed devices).

30
The SIE (Serial Interface Engine)
Serial
D
Interface
Bytes
Engine
D
(SIE)
USB
Transceiver
31
Packets
32
USB Packets

USB data travels in packets
Identified by Packet ID (PID)
Token packet tells whats coming
Data packets deliver bytes
Handshake packets report success or otherwise

33
Packet IDs (PIDS)

Token Packets
IN, OUT, SOF, SETUP
Data Packets
DATA0, DATA1 (USB LS/FS)
DATA2, MDATA (USB HS)
Handshake Packets
ACK, NAK, STALL (USB LS/FS)
NYET (USB HS)

34
Handshaking Packets

Used to ensure correct data delivery on Control,
Bulk and Interrupt Transfers
ACK Received with out Error
NAK Device Busy, has no data
Stall Unsupported Request, Request Failed
No Response Request not received or corrupt,
will be retried up to 3 times.

35
Packets Identified by PIDS
36
Three Packet Types
37
Transfers
38
USB Transfer Types

Bulk
Guaranteed accuracy, but delivery time is
variable
Best for bursty data
Isochronous
Guaranteed delivery time, but accuracy is not
guaranteed
Control
Enumeration and device control
Interrupt
Predictable polling time

39
USB Transfers

USB Transfers Occur in 1ms Frames (USB 2.0 adds
125 uS Microframes)
Host sends SOF (Start Of Frame) token every 1ms
Host schedules packets inside frames.

40
Anatomy of a USB Frame
1 msec frame
...
SOF
SOF
Video
Audio
Mouse
Control
Printer
Printer
Isochronous
Interrupt
Control
Bulk

12MHz 1.5MB/s or 1500 bytes/ms
Isochronous/Interrupt traffic have guaranteed
bandwidth
Control traffic is best-effort
Bulk uses what is left
Actual scheduling order depends on host
controller
UHCI, OHCI

41
Packet Sizes
42
Bulk IN Transfer (a)
H
D
H
H
H
D
D
D
C
C
A
E
C
A
E
C
A
R
A
A
R
A
Payload
Payload
I
D
N
R
I
D
N
R
T
C
T
C
C
C
N
D
D
C
N
D
D
C
Data
Data
A
K
A
K
1
1
R
P
5
R
P
5
1
0
6
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
H/S Pkt
goodnote the data toggle
good
43
Bulk IN Transfer (b)
H
D
H
H
D
D
H
H
D
D
C
C
A
E
C
A
E
C
A
E
C
N
A
A
A
A
R
R
Payload
Payload
I
D
N
R
I
D
N
R
I
D
N
R
A
T
C
T
C
C
C
N
D
D
C
N
D
D
C
Data
Data
N
D
D
C
K
A
K
A
K
1
1
R
P
5
R
P
5
R
P
5
1
6
0
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
H/S Pkt
Token Packet
H/S Pkt
good
good
not ready
44
Bulk IN Transfer (c)
H
(H)
D
H
H
D
D
D
C
C
A
E
C
A
E
C
A
A
A
R
R
Payload
Payload
I
D
N
R
I
D
N
R
T
T
C
C
C
N
D
D
C
Data
N
D
D
C
Data
A
1
A
1
K
R
P
5
R
P
5
1
1
6
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
goodnote same data and data toggle
host sees error no response
45
Bulk IN Transfer (d)
H
D
H
(D)
S
A
E
C
A
E
C
T
I
D
N
R
I
D
N
R
A
N
D
D
C
N
D
D
C
L
R
P
5
R
P
5
L
Token Packet
Token Packet
H/S Pkt
device has a problem
device detects token error or does not respond
46
Bulk OUT Transfer (a)
H
H
D
H
D
H
D
D
C
C
A
E
C
A
E
C
O
O
A
A
A
A
R
R
Payload
Payload
D
N
R
D
N
R
U
T
C
U
T
C
C
C
D
D
C
D
D
C
Data
Data
T
T
A
K
A
K
1
1
R
P
5
R
P
5
0
1
6
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
H/S Pkt
goodnote the data toggle
good
47
Bulk OUT Transfer (b)
H
D
H
H
D
H
D
H
H
D
D
D
C
C
C
A
E
C
A
E
C
A
E
C
O
A
A
A
A
A
N
R
O
R
O
R
Payload
Payload
Payload
D
N
R
D
N
R
D
N
R
U
T
C
T
C
T
A
C
U
C
U
C
D
D
C
Data
Data
Data
D
D
C
D
D
C
T
A
K
A
K
A
K
1
T
1
T
1
R
P
5
R
P
5
R
P
5
1
6
0
6
0
6
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
good
good
device not ready for data host sends data anyway
48
Bulk OUT Transfer (c)
H
(D)
H
H
D
H
D
D
C
C
A
E
C
A
E
C
O
A
O
A
A
R
R
Payload
Payload
D
N
R
D
N
R
U
T
U
T
C
C
C
D
D
C
D
D
Data
C
Data
T
A
T
A
K
1
1
R
P
5
R
P
5
1
1
6
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
good
device sees error no response
49
Bulk OUT Transfer (d)
(D)
H
H
H
H
D
D
C
D
C
S
A
E
A
E
C
C
A
O
R
A
O
R
T
Payload
Payload
D
N
R
D
N
R
T
U
C
T
U
A
C
D
D
C
Data
Data
D
D
C
A
T
T
1
A
1
L
R
P
5
R
P
5
1
6
1
6
L
Data Packet
Token Packet
Token Packet
Data Packet
H/S Pkt
device detects token error
device has problem
50
Control Transfer
H
H
D
D
C
S
A
E
C
A
8 bytes
R
A
E
D
N
R
SETUP
T
Setup
C
C
T
D
D
C
A
Data
1
K
U
R
P
5
0
6
P
Data Packet
H/S Pkt
Token Packet
H
D
H
D
C
A
E
C
A
R
A
I
D
N
R
Payload
DATA
T
C
C
N
D
D
C
Data
A
1
K
R
P
5
1
6
Data Packet
Token Packet
H/S Pkt
H
H
D
H
H
D
D
D
C
C
A
E
C
A
E
C
A
O
A
O
R
N
R
A
D
N
R
D
N
R
T
U
T
U
C
A
C
C
HANDSHAKE
D
D
C
D
D
C
A
T
1
K
A
T
1
K
R
P
5
R
P
5
1
1
6
6
Token Packet
Data Pkt
Token Packet
Data Pkt
H/S Pkt
H/S Pkt
Control operation
Control operation
not completed
completed
51
Interrupt IN OUT
H
D
H
H
H
D
D
D
C
C
A
E
C
A
E
C
A
A
A
A
R
R
Payload
Payload
I
D
N
R
I
D
N
R
T
C
T
C
C
C
N
D
D
C
Data
N
D
D
C
Data
A
K
A
K
1
1
R
P
5
R
P
5
1
0
6
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
H/S Pkt
goodnote the data toggle
good
H
H
D
H
D
H
D
D
C
C
A
E
C
A
E
C
O
O
A
A
A
A
R
R
Payload
Payload
D
N
R
D
N
R
U
U
T
C
C
T
C
C
D
D
C
D
D
C
Data
Data
T
T
A
1
K
A
1
K
R
P
5
R
P
5
0
1
6
6
Token Packet
Token Packet
Data Packet
Data Packet
H/S Pkt
H/S Pkt
goodnote the data toggle
good
Interrupt transfers are indistinguishable from
BULK transfers. They occur at most once per
frame.
52
Isochronous Transfer
H
D
D
C
A
E
C
A
Payload
R
I
D
N
R
T
C
N
D
D
C
Data
A
1
R
P
5
0
6
Token Packet
Data Packet
H
H
D
C
A
E
C
O
A
Payload
R
D
N
R
U
T
C
D
D
C
Data
T
A
1
R
P
5
0
6
Token Packet
Data Packet
Note Always DATA0 PID, no ACK
53
Requests
54
Standard USB Requests

Get Status
Set Address
Get Descriptor
Set Descriptor
Get Configuration
Set Configuration
Get Interface
Set Interface

Set Feature
Clear Feature
Sync Frame

55
Class Specific Requests

Specific to a given class, see the class
specification for details.
Examples
The Human Interface Device (HID) Class adds Get
Report and Set Report requests
The Hub Class adds a Get Port Status request

56
Enumeration

The user plugs the device into a USB port.
The hub detects the device.
The host learns of the devices presence from the
hub (Get Port Status Request)
The hub detects whether a device is Low speed or
Full Speed.
The hub resets the device.
The host learns if a full speed device supports
high speed.
The hub establishes a signal path between the
device and the bus.
The host sends a Get Descriptor Request to learn
the maximum packet size of the default pipe.
The host assigns an address (Set Address
Request).
The host learn about a devices abilities (Get
Descriptor Request).
The host assigns and loads a device driver.
The hosts device driver selects a configuration
(Set Configuration Request).

57
Operating System Interface
58
Host Controller Driver

Fundamental component of Operating System support
for USB
USB host controllers are PCI devices
What Does it Do?
Handles USB peripheral enumeration
Provides USB services for higher level drivers.
All access to USB peripherals is via these
services

59
Which OSs support USB

Pretty much all of themMore and more every day
Windows
MacOS
Linux
Solaris
VxWorks

60
Windows 95 OSR2.1

Microsofts first attempt to support USB
Only available to OEMs
Full of bugs
No HID support
Avoid it!

61
Windows 98/98SE

First Microsoft OS with full USB support
Class drivers for HID and USB speakers
98SE fixed a few minor bugs, enhanced
performance, added class drivers for USB modems

62
Windows Me (Millennium)

Windows 98 was supposed to be the last OS in the
Win9x family, but...
Follow on to Windows 98
Adds performance tweaks, bug fixes, USB audio
without clicks and pops, USB Mass Storage class
driver

63
Windows NT 4

NO SUPPORT FOR USB PROVIDED BY Microsoft!!!!
3rd party NT 4 USB drivers are available

64
Windows 2000

Robust USB Support including USB 2.0 High Speed
Shares common driver model (WDM) with Windows 98

65
Windows XP

Microsofts unified home/business operating
system
Based on Windows 2000
Same basic USB support as Windows 2000 with some
changes under the hood
Supports USB 2.0 High Speed

66
USB Peripheral Drivers

Class Drivers
Generic driver that supports a certain class of
device
Human Interface Devices (HID), USB hubs,
speakers, mass storage, modems
Note Not all USB Classes that are defined by the
USB-IF are implemented!!! Check your target OS
for support. (i.e. I know of no OS that has
implemented the Firmware Update Class)
Custom Drivers
Operating Systems often include vendor specific
drivers that have passed certification (e.g. WHQL)

67
HID Class

Built into Windows 98 (or later)
No need to write (or install) a driver!
Used by mice and keyboards, but can be used for
custom devices also.
Communicates with devices using reports
Set Report, Get Report
Full Spec at http//www.usb.org
You need the spec, and the HID Usage Tables

68
Custom Device Driver Options

Look for an Open Source Device Driver
http//libusb-win32.sourceforge.net (Windows)
http//libusb.sourceforge.net (Linux and others)
Use a General Purpose Device Driver
Write a Proprietary Custom Device Driver (or
have it written for you by a consultant)

69
Generic USB Device Drivers (for Windows OSs)

Check your silicon manufacturer, they may have a
general purpose driver you can use with their
silicon (Cypress and FTDI both do)
Thesycon USBIO (http//www.thesycon.de)
MCCI Virtual COM port driver (http//www.mcci.com)
Jungo (http//www.jungo.com)

70
Writing a Device Driver

Requires Specialized Knowledge (WDM and USBDI,
Kernel Debuggers, etc.)
Long Learning Curve (i.e. gt6months)
Not very well documented
Avoid this if you can!!!

71
Certifications and Logos

USB Implementers Forum Certification
Needed to use the new USB Certified Logos
Join the USB-IF or become a non-member Logo
Licensee
Attend a Plug-Fest or have your device tested
for compliance by an independent lab
Windows Hardware Quality Labs (WHQL)
Certification
Download the HCT and run the applicable tests (if
a self test is permitted for your device) or have
your device tested for compliance by an
independent lab

72
Some Considerations for DSP Applications
73
USB Silicon Options

USB Transceiver Only
Cypress TX2, Phillips, etc.
These are primarily intended for FPGAs that
implement a Serial Interface Engine (SIE)
USB Transciever SIE
Cypress SX2, Phillips, etc.
This would be a good option for DSPs without USB
support
USB Transciever SIE Microprocessor
Cypress EZ-USB, EZ-USB FX, EZ-USB-FX2, Microchip
USB PIC, DSPs that have USB Support
This would also be a good option for DSPs
without USB support
Fixed Function Devices
FTDI USB to Serial Converter Chips (This is a
good option for DSPs)
USB to ATAPI Bridge Chips

74
USB Transfer Types

Since some applications for Digital Signal
Processing are Stream operations you might
think that Isochronous transfers are the most
appropriate type to use. Sometimes, but not
alwaysConsider using RAM buffers and a Bulk or
Interrupt Transfer Type.
In lower bandwidth applications, consider the
FTDI USB to Serial Converter, they are a good
shortcut if you can use them.

75
USB Resources
76
USB Resources Books