Class-Specific AS interface descriptorįor details on this specification, refer to ADC-2 4.9.2.Īn AS interface descriptor must start with alternate setting zero with no endpoint (no bandwidth consumption) and further alternate settings must be specified in ascending order in compatible USB Audio 2.0 hardware.Īn alternate setting with a format that is not supported by the driver will be ignored.Įach non-zero alternate setting must specify an isochronous data endpoint, and optionally a feedback endpoint. The following subsections provide comments on some specific descriptor types. The driver supports all descriptor types defined in ADC-2, section 4. A function with an audio control interface but no streaming interface is not supported. DescriptorsĪn audio function must implement exactly one AudioControl Interface Descriptor (ADC-2 4.7) and one or more AudioStreaming Interface Descriptors (ADC-2 4.9). This means that the deviation of actual packet size from nominal size must not exceed +/- one audio slot (audio slot = channel count samples). The size of isochronous packets created by the device must be within the limits specified in FMT-2.0 section 2.3.1.1. The driver handles the Adaptive IN stream in the same way as an Asynchronous IN stream. If such an endpoint is present in the alternate setting, it will be ignored. There is currently limited support for devices using a shared clock for multiple endpoints.įor the Adaptive IN case the driver does not support a feedforward endpoint. The driver does not support implicit feedback. A feedback endpoint must be implemented in the respective alternate setting of the AS interface. The driver supports the following endpoint synchronization types (USB-2 5.12.4.1):įor the asynchronous OUT case the driver supports explicit feedback only. If a device implements multiple clock source entities and a clock selector, then the driver will use the clock source that is selected by default and will not modify the clock selector’s position.Ī Processing Unit (ADC-2 3.13.9) with more than one input pin is not supported.Īn Extension Unit (ADC-2 3.13.10) with more than one input pin is not supported.Ĭyclic paths in the topology are not allowed. The driver supports one single clock source only. The clock path may optionally include Clock Multiplier and Clock Selector units and must end in a Clock Source Entity. The driver supports all entity types defined in ADC-2 3.13.Įach Terminal Entity must have a valid clock connection in compatible USB Audio 2.0 hardware. This section describes the features of the USB Audio 2.0 driver.
An alternate setting which specifies another format defined in FMT-2, or an unknown format, will be ignored. The driver supports the formats listed below. The USB-IF is a special interest group that maintains the Official USB Specification, test specifications and tools. FMT-2 refers to the Audio Data Formats specification, Release 2.0.ADC-2 refers to the USB Device Class Definition for Audio Devices, Release 2.0.
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