tailieunhanh - USB Complete fourth- P21

USB Complete fourth- P21:This book focuses on Windows programming for PCs, but other computers and operating systems also have USB support, including Linux and Apple Computer’s Macintosh. Some real-time kernels also support USB. | Chapter 7 software Consulting GmbH yes that spelling is correct has a USBIO Development Kit with an ACM driver. Content Security The content security class defines a way to control access to files music video or other data transmitted on the bus. The control can use either of two defined content security methods basic authorization or digital transmission content protection DTCP . Documentation In addition to the main class specification each content security method CSM has its own specification document. The DTCP specification and license information are available from the Digital Transmission Licensing Administrator . Overview The class defines a protocol for activating and deactivating a content security method and for associating a content security method to a channel. A channel represents a relationship between an interface or endpoint and one or more CSMs. Only one CSM can be active on a channel at a time. Basic authorization also known as Content Security Method 1 or CSM-1 consists only of the class-specific request Get_Unique_ID which enables a host to request an ID value from a device. CSM-2 implements DTCP which prevents unauthorized copying of audio and video entertainment content via USB and other buses. A content provider can use DTCP to specify whether copying is allowed identify authorized users and specify an encryption method. A DTCP interface must have an interrupt endpoint in each direction for sending and receiving event notifications. A content provider who wants to use DTCP must sign a license agreement and pay an annual not trivial fee. Two additional CSMs that don t have USB specifications at this writing are open copy protection system CSM-3 and elliptic curve content protection protocol CSM-4 . 176 Device Classes Descriptors In an interface descriptor bInterfaceClass 0Dh declares the content security class. The class has four class-specific descriptors. CSM-2 defines a string descriptor for the string Digital Transmission .