Components of USB

Components of USB The foundation for a test approach requires a basic understanding of functional dependency and relationships. However, the order in which to go about beginning the actual approach may differ from the order of logical dependency. A tip in starting is to approach testing USB from a user point of view, keeping in mind the coverage of the logical and physical integration and cross–dependencies, in order to affirm completeness in coverage. The information in the following paragraphs encourage the creation of a simple test approach. The following diagram shows the USB architecture for an automotive computing device: Transfer Types USB supports the 4 basic transfer types listed below. For more information, see Further Reference_apctest_Further_Reference. • Interrupt (Keyboard, Legacy) • Bulk (CUE®, Vetronix® Box) • Isochronous (CD Changer) • Control (All) Built on Thursday, January 25, 2001 How WCEfA USB is different from Desktop PCs The primary differentiating factor between WCEfA USB and Desktop PC USB is the type of physical connector. Automotive computing devices use the Hiroshi type connector. In addition to the data and 5 volt power, this connector provides the 12 volts typically found in the car environment. In the car environment, the USB chain experiences high frequency power cycles from the root node. To attach a function, use the USBDeviceAttach function in the USB client driver. To detach a function, use the USB_CLOSE_DEVICE handler of the USBDeviceNotifications function in the USB client driver. The following list describes hardware actions and the expected response for each: • Warm boot – the attach function is called. • Hot unplug – the detach function is called. • Hot plug–in – the attach function is called if the device driver is already registered. • Ignition Off/Faceplate Detached – nothing is called. • Unplug and Plug during Ignition Off – nothing is called. • Ignition On/Faceplate Attached – the USB host controller enumerates all the USB devices connected. A thread—with the highest priority—will call the detach function of each loaded device driver, one by one. The same thread will call the attach function for all the currently connected device drivers, one by one, if the device driver is registered. Built on Thursday, January 25, 2001 Send USB Configurations A USB network is composed of a master host computer that is connected to slave USB devices. These devices may have a single function, such as a cell phone, or may contain a hub connection that allows other USB devices to be chained to them. This creates a tiered-star architecture that may be expanded to multiple levels. Examples include the following: A USB network may support up to 127 devices. This limit is due to the device address field being limited to 7 bits. The Auto PC is limited to four tiers and only one hub below the host hub. This counts the Auto PC as the first tier with three layers below it. Built on Thursday, January 25, 2001 Send feedback to MSDN. Look here for MSDN Online USB Connectivity USB offers a reliable, high-speed alternative to a standard serial port for connecting a Windows CE-based platform to a desktop computer. Windows CE 2.10 and 2.12, however, could not support USB connectivity to desktop systems, unless an OEM implemented that functionality. Windows CE 3.0 and later, however, do offer connectivity through USB. Windows CE 3.0 and later provide a USB Function controller driver for Windows CE-based platforms that include the appropriate USB Function controller hardware. By means of this driver, the USB Function controller hardware appears to Windows CE as a virtual serial port. Similarly, the desktop computer must have a similar host-side USB serial driver. With the Windows CE-based platform and the desktop computer so configured, the standard serial-port based mechanisms for connectivity can be used over a USB connection. OEMs can find the files necessary for implementing USB connectivity in the platform\cepc\drivers\serial_sl11\ directory of their Microsoft Windows CE Platform Builder installations. These files support the Scanlogic Corporation’s SL11 USB Function controller chipset. For complete information on implementing a virtual serial port via USB on a Windows CE-based platform, see Sample USB Function Controller Driver. There is, however, still no support for making a Windows CE–based platform itself appear as a USB peripheral to other host computers. This is because Windows CE only implements the host side of the USB client/host architecture. That is, the HCD and USBD modules supplied in Windows CE do not provide facilities to connect a Windows CE–based platform to a desktop computer that is running as a USB host. An OEM could implement this functionality if desired, although, as with the above connectivity scenarios, the Windows CE-based platform would still require USB Function controller hardware. Built on Wednesday, October 04, 2000 Send feedback to MSDN. Look here for MSDN Online resources. USB Connector The connectors on the reference platforms are the standard 4-pin USB type intended for the desktop environment and are only used during development and testing. The Auto PC reference hardware documentation refers to an eight-pin connector designed by Hirose (part number GT17-8DP-DS) and meant for a car’s high- vibration and wide-temperature-range environment. The pinout is as follows: Pin Number Pin Function 1 +5V 2 Data - 3 Data + 4 GND 5 GND 6 Wakeup2 7 Remote Power 8 +12V Main battery Two wires are used for the USB standard serial data bus. This data bus is shared by the Auto PC and its USB slave devices. The data rate is typically 12 megabits per second (Mbps), but there is an optional 1.5 Mbps mode. In accordance to the USB standard, the data is differentially driven to improve noise immunity. The USB connector can also supply power to the hubs and devices on the USB network. While some devices are self-powered from their own power supplies, others pull power from the USB connector. The Auto PC USB connector supplies two power sources of +5V and +12V. The +5V supply is specified by the USB standard and is required to provide a maximum of 600 mA continuous. The +12V line is added by the Auto PC design and continuously supplies a maximum of 3 A. The Auto PC USB connector also adds two signal lines for use in wakeup modes (labeled Wakeup2 and Remote Battery). The OEM system designer can use these signal lines to allow USB peripherals to signal the Power Management System to trigger a power event. This allows the Auto PC to transition from a powered-down state to a partial-power state to process information from the USB peripheral; for example, to store a page message. See the Power Management specification for more information. Built on Thursday, January 25, 2001 . Components of USB The foundation for a test approach requires a basic understanding of functional dependency and relationships from the order of logical dependency. A tip in starting is to approach testing USB from a user point of view, keeping in mind the coverage of the logical