UAC麦克见音频同步端点描述符

UAC音频采用同步传输，故数据传输的端点必须为同步传输。
端点描述符的数据结构如下：

关于同步传输可详见：http://www.usbzh.com/article/detail-118.html

标准端点描述符

代码如下：

/* USB_DT_ENDPOINT: Endpoint descriptor */
struct usb_endpoint_descriptor {
    __u8 bLength;
    __u8 bDescriptorType;
    __u8 bEndpointAddress;
    __u8 bmAttributes;
    __le16 wMaxPacketSize;
    __u8 bInterval; /* NOTE:  these two are _only_ in audio endpoints. */ /* use USB_DT_ENDPOINT*_SIZE in bLength, not sizeof. */
    __u8 bRefresh;
    __u8 bSynchAddress;
}
__attribute__((packed));
/* Standard ISO IN Endpoint Descriptor */
static struct usb_endpoint_descriptor microphone_as_ep_in_desc = {.bLength = USB_DT_ENDPOINT_AUDIO_SIZE,
    .bDescriptorType = USB_DT_ENDPOINT,
    .bEndpointAddress = USB_DIR_IN,
    .bmAttributes = USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_SYNC_ASYNC,
    .wMaxPacketSize = cpu_to_le16(UAC1_IN_EP_MAX_PACKET_SIZE),
    .bInterval = 4,
};

关于端点描述符各字段的解释详见：http://www.usbzh.com/article/detail-56.html

模拟设备信息（ Free Device Monitoring Studio 抓取

• descriptors[9] = “Endpoint Descriptor”
• bLength = 9
• bDescriptorType = USB_ENDPOINT_DESCRIPTOR_TYPE(5)
• bEndpointAddress = 3
• Reserved = 0
• Direction = Input type = Isochronous(1) reserved = 1
• wMaxPacketSize = 32
• bInterval = 4
• unknown = 0, 0

UAC音频特定类的音频同步端点描述符

源码：

struct uac_iso_endpoint_descriptor {
    __u8 bLength; /* in bytes: 7 */
    __u8 bDescriptorType; /* USB_DT_CS_ENDPOINT */
    __u8 bDescriptorSubtype; /* EP_GENERAL */
    __u8 bmAttributes;
    __u8 bLockDelayUnits;
    __le16 wLockDelay;
}
__attribute__((packed));
/* Class-specific AS ISO IN Endpoint Descriptor */
static struct uac_iso_endpoint_descriptor microphone_as_iso_in_desc = {.bLength = UAC_ISO_ENDPOINT_DESC_SIZE,
    .bDescriptorType = USB_DT_CS_ENDPOINT,
    .bDescriptorSubtype = UAC_EP_GENERAL,
    .bmAttributes = 1,
    .bLockDelayUnits = 1,
    .wLockDelay = cpu_to_le16(1),
};

模拟设备信息（ Free Device Monitoring Studio 抓取

• descriptors[10] = “Class-Specific Endpoint Descriptor”
• bLength = 7
• bDescriptorType = CS_ENDPOINT(37)
• iso_endpoint =
• bmAttributes = 1
  • controls =
  • iso_data =
  • PitchControl = 1
  • DataOverrunControl = 0
  • DataUnderrunControl = 0
  • Reserved = 0
  • bmControls = 00000001
• bLockDelayUnits = Milliseconds(1)
• wLockDelay = 1