我正在尝试通过USB从我的嵌入式Linux设备向/从Windows主机发送/接收音频 .
据我所知，通过USB发送音频有2种协议 - USB音频等级1和2（UAC1和UAC2） . 我在这里解释了它们：http://www.thewelltemperedcomputer.com/HW/USB_Audio.htm .
我目前使用Linux中现有的UAC1设备驱动程序从主机PC获取音频 . 这个对我有用 . 我现在正在尝试更改设备驱动程序，以便能够将音频发送到主机PC .
我看到's a UAC2 driver (in the latest Linux kernel) that both sends and receives audio from the host. But I'喜欢有一个UAC1驱动程序，这样我就不必在Windows主机上安装任何额外的驱动程序（尤其是我必须购买的驱动程序：http://www.thesycon.de/eng/usb_audiodriver.shtml） .
我在linux / drivers / usb / gadget / f_audio.c修改了linux设备驱动程序（我使用的是较旧的内核） . 我已经更改了USB标头描述符，以包含用于向主机发送音频的额外 endpoints .
static struct usb_descriptor_header *hs_audio_desc[] = {
(struct usb_descriptor_header *)&std_ac_if_desc,
(struct usb_descriptor_header *)&ac_hdr_desc,
(struct usb_descriptor_header *)&usb_it_desc,
(struct usb_descriptor_header *)&usb_ot_desc,
(struct usb_descriptor_header *)&std_as_out_if0_desc,
(struct usb_descriptor_header *)&std_as_out_if1_desc,
(struct usb_descriptor_header *)&as_out_hdr_desc,
(struct usb_descriptor_header *)&as_out_fmt1_desc,
(struct usb_descriptor_header *)&hs_epout_desc,
(struct usb_descriptor_header *)&as_iso_out_desc,
(struct usb_descriptor_header *)&std_as_in_if0_desc,
(struct usb_descriptor_header *)&std_as_in_if1_desc,
(struct usb_descriptor_header *)&as_in_hdr_desc,
(struct usb_descriptor_header *)&as_in_fmt1_desc,
(struct usb_descriptor_header *)&hs_epin_desc,
(struct usb_descriptor_header *)&as_iso_in_desc,
NULL,
};
OUT endpoints 定义为：
struct usb_endpoint_descriptor hs_epout_desc = {
.bLength = USB_DT_ENDPOINT_SIZE,
.bDescriptorType = USB_DT_ENDPOINT,
.bmAttributes = USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_SYNC_ASYNC,
.wMaxPacketSize = __constant_cpu_to_le16(OUT_EP_MAX_PACKET_SIZE),
.bInterval = 4,
};
IN endpoints 定义为：
struct usb_endpoint_descriptor hs_epin_desc = {
.bLength = USB_DT_ENDPOINT_SIZE,
.bDescriptorType = USB_DT_ENDPOINT,
.bEndpointAddress = USB_DIR_IN,
.bmAttributes = USB_ENDPOINT_XFER_ISOC | USB_ENDPOINT_SYNC_ASYNC,
.wMaxPacketSize = __constant_cpu_to_le16(OUT_EP_MAX_PACKET_SIZE),
.bInterval = 4,
};
在epautoconf.c中，bEndpointAddress字段通常与 endpoints 号进行“或”运算 . 在我看来，我发现这种情况正在发生 . 当我在epautoconf.c中打印时，我的OUT endpoints 的'bEndpointAddress'字段是0x01，而我的IN endpoints 是0x81 . 但是我无法在主机端看到它 . 在我的Windows PC上，我使用USB View工具查看描述符，我看到值为0x00和0x80 .
什么可能改变了bEndpointAdress的 Value ？
这些是我在Windows中使用USB View工具看到的USB描述符：
Device Descriptor:
bcdUSB: 0x0200
bDeviceClass: 0x00
bDeviceSubClass: 0x00
bDeviceProtocol: 0x00
bMaxPacketSize0: 0x40 (64)
idVendor: 0x1D6B
idProduct: 0x0101
bcdDevice: 0x0316
iManufacturer: 0x01
0x0409: "Linux 3.2.0 with musb-hdrc"
iProduct: 0x02
0x0409: "Linux USB Audio Gadget"
iSerialNumber: 0x00
bNumConfigurations: 0x01
ConnectionStatus: DeviceConnected
Current Config Value: 0x01
Device Bus Speed: High
Device Address: 0x13
Open Pipes: 0
Configuration Descriptor:
wTotalLength: 0x0095
bNumInterfaces: 0x03
bConfigurationValue: 0x01
iConfiguration: 0x00
bmAttributes: 0xC0 (Bus Powered Self Powered )
MaxPower: 0x01 (2 Ma)
Interface Descriptor:
bInterfaceNumber: 0x00
bAlternateSetting: 0x00
bNumEndpoints: 0x00
bInterfaceClass: 0x01 (Audio)
bInterfaceSubClass: 0x01 (Audio Control)
bInterfaceProtocol: 0x00
iInterface: 0x04
0x0409: "Topology Control"
Audio Control Interface Header Descriptor:
bLength: 0x0A
bDescriptorType: 0x24
bDescriptorSubtype: 0x01
bcdADC: 0x0100
wTotalLength: 0x001F
bInCollection: 0x02
baInterfaceNr[1]: 0x01
baInterfaceNr[2]: 0x02
Audio Control Input Terminal Descriptor:
bLength: 0x0C
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bTerminalID: 0x02
wTerminalType: 0x0201 (Microphone)
bAssocTerminal: 0x00
bNrChannels: 0x02
wChannelConfig: 0x0003
iChannelNames: 0x00
iTerminal: 0x07
Audio Control Output Terminal Descriptor:
bLength: 0x09
bDescriptorType: 0x24
bDescriptorSubtype: 0x03
bTerminalID: 0x01
wTerminalType: 0x0301 (Speaker)
bAssocTerminal: 0x00
bSoruceID: 0x00
iTerminal: 0x09
Interface Descriptor:
bInterfaceNumber: 0x01
bAlternateSetting: 0x00
bNumEndpoints: 0x00
bInterfaceClass: 0x01 (Audio)
bInterfaceSubClass: 0x02 (Audio Streaming)
bInterfaceProtocol: 0x00
iInterface: 0x0B
0x0409: "Playback Inactive"
Interface Descriptor:
bInterfaceNumber: 0x01
bAlternateSetting: 0x01
bNumEndpoints: 0x01
bInterfaceClass: 0x01 (Audio)
bInterfaceSubClass: 0x02 (Audio Streaming)
bInterfaceProtocol: 0x00
iInterface: 0x0C
0x0409: "Playback Active"
Audio Streaming Class Specific Interface Descriptor:
bLength: 0x07
bDescriptorType: 0x24
bDescriptorSubtype: 0x01
bTerminalLink: 0x01
bDelay: 0x01
wFormatTag: 0x0001 (PCM)
Audio Streaming Format Type Descriptor:
bLength: 0x0B
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bFormatType: 0x01
bNrChannels: 0x00
bSubframeSize: 0x02
bBitResolution: 0x10
bSamFreqType: 0x01
tSamFreq[1]: 0x00BB80 (48000 Hz)
Endpoint Descriptor:
bEndpointAddress: 0x00 OUT
Transfer Type: Isochronous
wMaxPacketSize: 0x00C8 (200)
bInterval: 0x04
Audio Streaming Class Specific Audio Data Endpoint Descriptor:
bLength: 0x07
bDescriptorType: 0x25
bDescriptorSubtype: 0x01
bmAttributes: 0x00
bLockDelayUnits: 0x00
wLockDelay: 0x0000
Interface Descriptor:
bInterfaceNumber: 0x02
bAlternateSetting: 0x00
bNumEndpoints: 0x00
bInterfaceClass: 0x01 (Audio)
bInterfaceSubClass: 0x02 (Audio Streaming)
bInterfaceProtocol: 0x00
iInterface: 0x0D
0x0409: "Capture Inactive"
Interface Descriptor:
bInterfaceNumber: 0x02
bAlternateSetting: 0x01
bNumEndpoints: 0x01
bInterfaceClass: 0x01 (Audio)
bInterfaceSubClass: 0x02 (Audio Streaming)
bInterfaceProtocol: 0x00
iInterface: 0x0E
0x0409: "Capture Active"
Audio Streaming Class Specific Interface Descriptor:
bLength: 0x07
bDescriptorType: 0x24
bDescriptorSubtype: 0x01
bTerminalLink: 0x02
bDelay: 0x01
wFormatTag: 0x0001 (PCM)
Audio Streaming Format Type Descriptor:
bLength: 0x0B
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bFormatType: 0x01
bNrChannels: 0x00
bSubframeSize: 0x02
bBitResolution: 0x10
bSamFreqType: 0x01
tSamFreq[1]: 0x00BB80 (48000 Hz)
Endpoint Descriptor:
bEndpointAddress: 0x80 IN
Transfer Type: Isochronous
wMaxPacketSize: 0x00C8 (200)
bInterval: 0x04
Audio Streaming Class Specific Audio Data Endpoint Descriptor:
bLength: 0x07
bDescriptorType: 0x25
bDescriptorSubtype: 0x01
bmAttributes: 0x00
bLockDelayUnits: 0x00
wLockDelay: 0x0000
为什么Windows不安装UAC1驱动程序？
1 回答
对于我的第一个问题，我从linux-usb邮件列表中得到了答案 . 事实证明'epautoconf.c'不会改变'bEndpointAdress' . 所以我改变了'bEndpointAdress'定义中的值，现在正确地传达给主机 .
我使用此配置时Windows正确安装UAC1驱动程序：