1. USB Fundamentals and Applications for Digital Signal Processing
Greg Burk
J. Gordon Electronic Design
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USB 1.0 – The original spec, superseded quickly by USB 1.1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
Compaq
Intel
Microsoft
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 compatible—plug existing 1.1 devices into new 2.0 hosts
Backward compatible—plug 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 Applications Source: Beeman: www.usbonthego.com
Exchange pictures
Upload pictures to web
Print pictures
Camera
Cell Phone
Printer
Exchange songs
MP3 player
Exchange Contact info
Print call info
Synchronize phone list, meetings
Upload pictures
Download songs PC
Applications
Peripheral
Host

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:
(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, it’s not a drop-in replacement
It’s 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 (<= 500ma to each device)
Bus-Powered (<= 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: Devices are “self describing” Self-Powered
External Power Source (i.e. wall wart)
Batteries
Bus-Powered
Low Power Bus Powered (<= 100mA)
High Power Bus Powered >100mA, <=500mA)
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
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 “Tiered Star” Hub Device Device Device Device

23. USB Transfer Speeds USB 1.1: USB 2.0 Low speed is 1.5Mb/s
Full speed is 12Mb/s
USB 2.0
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 Configuration 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
OS Interface
Requests
Transfers
Packets
Signaling

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 don’t 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)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 what’s coming
Data packets deliver bytes
Handshake packets report success or otherwise

33. Packet IDs (PIDS) Token Packets Data Packets Handshake 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 Isochronous Control Interrupt
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 12MHz = 1.5MB/s or 1500 bytes/ms
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 Control Bulk Interrupt Isochronous 8, 16, 32, 64 1–64
1023 64
512
1024
USB 1.1
USB 2.0
Transfer Type
Packet Size

42. Bulk IN Transfer (a) good good—note the data toggle H D H H D HC D C A E C A E C A
Payload R A A R A I D N R I D N R
Payload T C C T C C N D D C
Data N D D C
Data A 1 K A 1 K R P 5 R P 5 1 6 6
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
good
good—note the data toggle
“H” means sent by the host, “D” means sent by the device.

43. Bulk IN Transfer (b) good not ready good H D H H D H D H PayloadC C D A E C C A E C A
Payload R A N A R A I D N R I D N R I D N R
Payload T C C A T C C N D D C
Data N D D C N D D C
Data A 1 K K A 1 K R P 5 R P 5 R P 5 1 6 6
Token Packet
Data Packet
H/S Pkt
Token Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
good
not ready
good

44. good—note same data and data toggle
Bulk IN Transfer (c) H D
(H) H D H D C D C A E C A E C A I D N R
Payload R A R A I D N R
Payload T C T C C N D D C
Data N D D C
Data A 1 A 1 K R P 5 R P 5 1 6 1 6
Token Packet
Data Packet
Token Packet
Data Packet
H/S Pkt
host sees error; no response
good—note same data and data toggle

45. Bulk IN Transfer (d) H D H (D) device has a problem5 R P 5 L
Token Packet
H/S Pkt
Token Packet
device has a problem
device detects token error
or does not respond

46. Bulk OUT Transfer (a) H H D H H D good good—note the data toggleC D C A E C A E C O A O D N R
Payload R A A R A D N R
Payload U T C C U T C C D D C
Data D D C
Data T A 1 K T A 1 K R P 5 R P 5 6 1 6
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
good
good—note the data toggle

47. Bulk OUT Transfer (b) good device not ready for dataH H D H H D H H D D D D A E C C C C O A E C A E C A D N R
Payload R A O A R N O A R A U T C D N R
Payload D N R
Payload C U T C A U T C C D D C
Data T D D C
Data D D C
Data R P 5 A 1 K T A 1 K T A 1 K 1 R P 5 R P 5 6 6 6
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
good
device not ready for data
host sends data anyway
good

48. Bulk OUT Transfer (c) H H (D) H H D device sees error; no response
Payload A
Payload R A D N R D N R U T C U T C C D D C
Data D D C
Data T A 1 T A 1 K R P 5 R P 5 1 6 1 6
Token Packet
Data Packet
Token Packet
Data Packet
H/S Pkt
device sees error; no response
good

49. Bulk OUT Transfer (d) device has problem device detects token error H
Payload R T O A
Payload R D N R U T C A U T C D D C
Data D D C
Data T A 1 L T A 1 R P 5 R P 5 1 6 L 1 6
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
device has problem
device detects token error

50. Control Transfer SETUP DATA HANDSHAKE Control operation
8 bytes R A D N R
SETUP T T
Setup C C D D C U A
Data 1 K R P 5 P 6
Token Packet
Data Packet
H/S Pkt H D H D C A E C A R A
DATA I D N R
Payload T C C N D D C
Data A 1 K R P 5 1 6
Token Packet
Data Packet
H/S Pkt H H D H H D D C D C A E C A E C O A R N O A R A D N R D N R
HANDSHAKE U T C A U T C C D D C D D C T A 1 K T A 1 K R P 5 R P 5 1 6 1 6
Token Packet
Data Pkt
H/S Pkt
Token Packet
Data Pkt
H/S Pkt
Control operation
Control operation
not completed
completed

51. Interrupt IN & OUT H D H H D H D C D C A E C A E C A
Payload R A A R A I D N R I D N R
Payload T C C T C C N D D C
Data N D D C
Data A 1 K A 1 K R P 5 R P 5 1 6 6
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
good
good—note the data toggle H H D H H D D C D C A E C A E C O A R A O
Payload A R A D N R D N R
Payload U T C C U T C C D D C
Data D D C
Data T A 1 K T A 1 K R P 5 R P 5 6 1 6
Token Packet
Data Packet
H/S Pkt
Token Packet
Data Packet
H/S Pkt
good
good—note the data toggle
Interrupt transfers are indistinguishable from BULK transfers. They occur at most once per frame.

52. Isochronous Transfer H D Payload Data H H Payload Data1 R P 5 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 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 host’s 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 OS’s support USB Pretty much all of them…More and more every day
Windows
MacOS
Linux
Solaris
VxWorks

60. Windows 95 OSR2.1 Microsoft’s 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 Microsoft’s 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
You need the spec, and the HID Usage Tables

68. Custom Device Driver Options
Look for an Open Source Device Driver
(Windows)
(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 OS’s)
Check your silicon manufacturer, they may have a general purpose driver you can use with their silicon (Cypress and FTDI both do)
Thesycon USBIO (
MCCI Virtual COM port driver (
Jungo (

70. Writing a Device Driver
Requires Specialized Knowledge (WDM and USBDI, Kernel Debuggers, etc.)
Long Learning Curve (i.e. >6months)
Not very well documented
Avoid this if you can!!!

71. Certifications and Logo’s
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 USB Transciever + SIE
Cypress TX2, Phillips, etc.
These are primarily intended for FPGA’s that implement a Serial Interface Engine (SIE)
USB Transciever + SIE
Cypress SX2, Phillips, etc.
This would be a good option for DSP’s without USB support
USB Transciever + SIE + Microprocessor
Cypress EZ-USB, EZ-USB FX, EZ-USB-FX2, Microchip USB PIC, DSP’s that have USB Support
This would also be a good option for DSP’s without USB support
Fixed Function Devices
FTDI USB to Serial Converter Chips (This is a good option for DSP’s)
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 always…Consider 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 Devices Windows Drivers (including USB)
Jan Axelson, USB Complete, Second Edition
John Hyde, USB Design By Example, Second Edition
Windows Drivers (including USB)
Walter Oney, Programming the Microsoft Windows Driver Model
Chris Cant, Writing Windows WDM Device Drivers

77. USB Resources: Internet
USB Specifications and Class Specifications
Draft docs
Bulletin board (Developer Forum)
Product information incl. chips

78. USB Resources: Consultants
J. Gordon Electronic Design
(763)
(A shameless plug for my employer)

79. Questions ?

80. Optional Topics (if there is time)
Optical Isolation and USB
USB Tools
USB Serial Numbers and Windows XP

81. A special thanks to Cypress Semiconductor for allowing use some of the included slides.