| To download a copy of this white paper click here.
Let USB-inSync take control of your time.
The USB-inSync provides a dedicated system reference clock in the root hub. Each device requiring timing and synchronisation information is provided an on-board clock which is accurately phase locked to all other USB-inSync device clocks on the hub via USB software protocol. USB-inSync devices automatically phase-lock to every other USB-inSync device connected to the same off-the-shelf USB port.
Standard USB
USB has achieved 100% market penetration in the notebook and desktop PC markets with every PC currently sold offering a minimum of two ports. The well-known advantages of the standard USB specification are summarized as follows:
• External serial bus
• Hi-Speed 12Mbps and Full-Speed 480Mbps bandwidth
• Plug-and-play installation
• Hot-swappable connection
• Expansion via random star topology
• Widespread PC compatibility & Low Cost
The standard USB specification is an expandable PC interface that can simultaneously control up to 127 devices (including expansion hubs) from a single USB port controller on a PC. Each hub may have up to 7 expansion ports and can be connected to other hubs in any random topology the user desires. USB is a serial bus that typically operates in a host (PC) – slave (device) configuration (see Figure 1).
Synchronization & Determinism
USB was designed to simultaneously operate different devices that vary in nature and function. It allows for multiple devices to simultaneously interact with the same PC – not for the devices to interact with each other in a real time sense. As a consequence USB is an “asynchronous” bus with poor levels of timing accuracy between devices on the same hub. The maximum levels of synchronization accuracy for typical USB devices are on the millisecond time scale – just good enough to synchronize a couple of PC audio speakers together (see below).
As an asynchronous bus USB has no timing resolution between different devices on the same hub. Multiple USB devices cannot be used in concert with each other (only simultaneously with the PC). In fact the use of multiple hubs in the connection topology further decreases the level of device synchronization (varying path lengths translate to varying propagation times for every device–host communications). With the standard USB framework there is no ability to provide synchronous real-time control or data acquisition for applications including test, measurement, control and automation. USB’s penetration in real-time markets such as test & measurement has been limited to data-upload applications and will continue as such if enhancements are not available. Consequently PC-controlled test and measurement devices still rely on cumbersome slow bus interfaces such as RS-232 and GPIB because they have good levels of synchronization.
What is USB-inSync?
A USB-inSync device is a USB compatible device that possesses all the characteristics of USB, but posses the feature enhancement of synchronization and deterministic timing capabilities over standard USB interfaces. All the devices on this USB tree are linked and can make use of this relationship. The availability Nanosecond phase-locking over standard USB traffic enables USB-inSync devices to be used for applications such as multi-channel test and measurement (see Figure 2).
In addition to phase-locking capabilities USB-inSync can also perform phase compensation to account for timing differences due to different connection path lengths. A USB-inSync Master Hub contains accurate timing reference system for all hubs to operate. Using a Master Hub at the root of the expansion tree automatically compensates for the phase differences that result from different connection distances and hub topologies with respect to the PC (see Figure 3).
USB-inSync Hardware Features
The USB-inSync hardware specification defines a dedicated system reference clock in the root hub. Each device requiring timing and synchronisation information is provided an on-board clock which is accurately phase locked to all other USB-inSync device clocks on the hub via USB software protocol. USB-inSync devices automatically phase-lock to every other USB-inSync device connected to the same off-the-shelf USB hub.
The key to USB-inSync working over standard USB hub and ports is that the hardware platform resides solely in the USB-inSync device itself. Fiberbyte enables hardware manufactures with the capabilities of USB-inSync through a USB OEM interface board that contains a programmable micro-controller allowing complete application specific device control (see right). When combined with the USB-inSync software platform full synchronization and deterministic capabilities can be implemented over standard USB hub architecture.
The inclusion of standard USB protocols allows potential users of USB-inSync to upgrade their current USB devices. Instead of costly re-engineering of the USB interface the enhancements of USB-inSync can be simply add to the existing interface. Likewise USB-inSync drivers are created in such as way that the existing software USB interface will require only an upgrade again purposely avoiding costly re-engineering.
USB has some other limitations with regards to test and measurement applications and deterministic control environments. Many test devices such as optical sources or function generators require more electrical power than the 500mA of current available over standard USB. USB-inSync provides for additional DC power to be supplied directly to the OEM board as required.
USB-inSync Software Features
The software platform is based on a software design philosophy to simultaneously process data from multiple devices via a threaded digital I/O command infrastructure. The engine is based on a COM driver which enables interfacing with any Windows based software application including MS Office, Visual Studio and National Instruments LabVIEW. The complete software interface provides simple connection points for both the application software in the PC and on-board the microcontroller located on the device.
Software platform features are summarized as:
• Current release is fully compatible with USB1.1 driver specification.
• Provides programmable access to all USB-inSync hardware
• COM engine supports interfacing with Windows 2000/XP OS
• Links multiple USB-inSync modules with multiple concurrent software applications.
• Enables USB-inSync, synchronization, data transfer, command transfer and hot plug.
• Includes Registration manager, Message processor, Event handler
• Multi-threaded I/O processing for deterministic sampling applications.
• LabView drivers for specific device implimentations
Summary
Fiberbyte has developed the USB-inSync specification with the aim of providing an open industry software specification with products available from multiple vendors residing on the same bus without conflict. USB-inSync is seen as the future of PC-based test and measurement platforms with an open accessible bus architecture based on the common USB bus.
USB-inSync Features
• Fully compatible with USB1.1 hardware and software.
• Nanosecond phase-locking between USB-inSync devices
• Nanosecond phase-compensation between expansion hubs
• Real-time sampling capabilities
• Supports addition of external DC power supply
• Supports both USB and FCI connector options
• Supports interfaces with any Windows 2000 / XP software application
USB-inSync Requirements
• Windows 2000 Home or Professional editions
• Windows XP Home or Professional editions
• Intel Pentium III PC or higher
• 128 MB RAM, 10MB hard disk space
• USB1.1 Host port
• USB-inSync embedded Device
To download a copy of this white paper click here.
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