UAC麦克风输出终端描述符

输出终端描述符在UAC规范的拓扑图中表示音频数据的输出端，该数据即将通过UAC的同步传输端点上报给主机。

输出终端描述符的数据配置如下：

输出终端描述符各字段的详解见：http://www.usbzh.com/article/detail-237.html

C语言结构体和初始化代码如下：

/* 4.3.2.2 Output Terminal Descriptor */
struct uac1_output_terminal_descriptor {
    __u8 bLength; /* in bytes: 9 */
    __u8 bDescriptorType; /* CS_INTERFACE descriptor type */
    __u8 bDescriptorSubtype; /* OUTPUT_TERMINAL descriptor subtype */
    __u8 bTerminalID; /* Constant uniquely terminal ID */
    __le16 wTerminalType; /* USB Audio Terminal Types */
    __u8 bAssocTerminal; /* ID of the Input Terminal associated */
    __u8 bSourceID; /* ID of the connected Unit or Terminal*/
    __u8 iTerminal;
}
__attribute__((packed));


static struct uac1_output_terminal_descriptor microphone_output_terminal_desc = {
    .bLength = UAC_DT_OUTPUT_TERMINAL_SIZE,
    .bDescriptorType = USB_DT_CS_INTERFACE,
    .bDescriptorSubtype = UAC_OUTPUT_TERMINAL,
    .bTerminalID = MICROPHONE_OUTPUT_TERMINAL_ID,
    .wTerminalType = UAC_TERMINAL_STREAMING,
    .bAssocTerminal = MICROPHONE_INPUT_TERMINAL_ID,
    .bSourceID = MICROPHONE_INPUT_TERMINAL_ID,
};

通过模拟设备信息（Free Device Monitoring Studio 抓取：

• descriptors[4] = “Class-Specific Interface Descriptor”
• bLength = 9
• bDescriptorType = CS_INTERFACE (36)
• bDescriptorSubtype = 3
• ac_interface =
• output_terminal =
• bTerminalID = 2
• wTerminalType = 257
• bAssocTerminal = 1
• bSourceID = 1
• bCSourceID = 0
• bmChannelConfig = 66569
• iChannelNames = 0
• bmControls = 513
• terminal_control =
• terminal =
• CopyProtect = 0
• ConnectorControl = 0
• OverloadControl = 0
• ClusterControl = 0
• UnderflowControl = 0
• OverflowControl = 0
• Reserved = 0
• bmControls = 0000000000000000
• iTerminal = 9