L_17

记一次USB声卡设计开发

目前笔者从事音频开发工作，借助公司硬件资源，给自己做了个迷你声卡，接下来让笔者介绍一下相关开发过程。

USB声卡，这里借助度娘的解释：USB声卡是插在USB口的声卡，通过USB总线与计算机系统链接。。。。。。

那么怎么DIY声卡需要些什么硬件资源呢？

1.具有USB和I2S相关外设的MCU 2.Codec(编码解码器) 3.输出输入接口及相关模电电路

如下简图：

我这里直接选用的MCU资源为NXP的RT1052，当然MCU大可不必选这么好的，选用STM32F1系列基本就可以，笔者主要为了可玩性，加一些算法效果所以选择了这款比较火的跨界处理器。Codec的选择根据自己想做到什么级别的吧，市面上的几块十几块几十块的都可以，我们主要需要了解的一些基本参数：动态范围，信噪比等等。另外模拟运放部分也很关键，总之音质的影响是方方面面的，如：USB Audio 同步问题，Codec选型配置问题，运放设计问题，电源问题都会影响声卡的参数。

如下实物图：

硬件配套全了，接下来开搞软件了，核心部分当然是USB Audio啦。这里笔者采用比较古老的Audio1.0标准开发的，主要原因是免驱，开发难度不会很大。对于USB Audio 的开发这里说比较关键的几点：

1.设备接口数量：如果要实现扬声器和录音功能，那么接口数量为：3个分别为 Control+Recoder+Speaker

2.音频流同步问题（缓冲区的处理方案，反馈端点的使用策略）具体可以参考我之前写的一个博客

https://blog.csdn.net/weixin_38426553/article/details/95383679

3.采样率，采样精度等等

4.每次修改usb audio配置后最好卸载之前的驱动，让PC重新配置相关驱动

下面分享一点点相关配置（一不小心做成了复合设备）：

/* Configuration, interface and endpoint. */

#define USB_DEVICE_CONFIGURATION_COUNT (1)

#define USB_DEVICE_STRING_COUNT (3)

#define USB_DEVICE_LANGUAGE_COUNT (1)

#define USB_DEVICE_INTERFACE_COUNT (6) //设备接口数量（Control+Recoder+Speaker+Contrl+ MIDI+HID）

#define USB_AUDIO_ENDPOINT_COUNT (1)

#define USB_AUDIO_SPEAKER_CONFIGURE_INDEX (1)

#define USB_COMPOSITE_CONFIGURE_INDEX (1)

/*接口计数，根据数量依次递增*/

#define USB_AUDIO_CONTROL_INTERFACE_INDEX (0)

#define USB_AUDIO_RECORDER_STREAM_INTERFACE_INDEX (1)

#define USB_AUDIO_SPEAKER_STREAM_INTERFACE_INDEX (2)

/*MIDI 独立拥有一个Contrl接口端点*/

#define USB_AUDIO_MIDI_INDEX (4)

#define USB_HID_INTERFACE_INDEX (5)

/*每个接口的端点数量*/

#define USB_AUDIO_CONTROL_ENDPOINT_COUNT (1)

#define USB_AUDIO_RECORDER_STREAM_ENDPOINT_COUNT (1)

#define USB_AUDIO_SPEAKER_STREAM_ENDPOINT_COUNT (2)

#define USB_HID_ENDPOINT_COUNT (2)

#define USB_AUDIO_MIDI_ENDPOINT_COUNT (2)

/*分配端点地址*/

#define USB_AUDIO_CONTROL_ENDPOINT (1)

#define USB_AUDIO_SPEAKER_STREAM_ENDPOINT (2)

#define USB_AUDIO_SPEAKER_FEEDBACK_ENDPOINT (2)

#define USB_AUDIO_RECORDER_STREAM_ENDPOINT (3)

#define USB_AUDIO_MIDI_ENDPOINT_IN (4)

#define USB_AUDIO_MIDI_ENDPOINT_OUT (4)

#define USB_HID_ENDPOINT_IN (5)

#define USB_HID_ENDPOINT_OUT (5)

/* Audio data format */

#define AUDIO_FORMAT_CHANNELS (0x02) //立体声模式

#define AUDIO_FORMAT_BITS (24) //数据宽度 24bit

#define AUDIO_FORMAT_SIZE (0x03) //数据长度 8*3

#define HS_ISO_IN_ENDP_PACKET_SIZE (AUDIO_SAMPLING_RATE_KHZ * AUDIO_FORMAT_CHANNELS * AUDIO_FORMAT_SIZE) //包大小，根据采样率，采样精度和通道数量选择

#define FS_ISO_IN_ENDP_PACKET_SIZE (AUDIO_SAMPLING_RATE_KHZ * AUDIO_FORMAT_CHANNELS * AUDIO_FORMAT_SIZE)

Audio描述符相关：

/**********************Audio Interface Descriptor(No.0):0x04**********************/

USB_DESCRIPTOR_LENGTH_INTERFACE, /* Size of this descriptor in bytes */

USB_DESCRIPTOR_TYPE_INTERFACE, /* INTERFACE Descriptor Type */

USB_AUDIO_CONTROL_INTERFACE_INDEX, /* Number of this interface. */

0x00U, /* Value used to select this alternate setting

for the interface identified in the prior field */

0x01U, /* Number of endpoints used by this

interface (excluding endpoint zero). (0 or 1)*/

USB_AUDIO_CLASS, /*The interface implements the Audio Interface class */

USB_SUBCLASS_AUDIOCONTROL, /*The interface implements the AUDIOCONTROL Subclass */

0x00U, /*The interface doesn't use any class-specific protocols */

0x00U, /* The device doesn't have a string descriptor describing this iInterface */

/*******************AC Header of Interface Descriptor:0x24 0x01*************************/

USB_AUDIO_CONTROL_INTERFACE_HEADER_LENGTH, /* Size of the descriptor, in bytes */

USB_DESCRIPTOR_TYPE_AUDIO_CS_INTERFACE, /* CS_INTERFACE Descriptor Type */

USB_DESCRIPTOR_SUBTYPE_AUDIO_CONTROL_HEADER, /* HEADER descriptor subtype */

0x00U, 0x01U, /* Audio Device version 1.00 */

0x48, 0x00U, /* Total number of bytes returned for the class-specific AudioControl interface descriptor. Includes

the combined length of this descriptor header and all Unit and Terminal descriptors. */

0x02U, /* The number of AudioStreaming and MIDIStreaming interfaces in the Audio Interface Collection to which this

AudioControl interface belongs */

USB_AUDIO_RECORDER_STREAM_INTERFACE_INDEX, /* Recorder interfaces in the Audio Interface baNumber is 0x01 */

USB_AUDIO_SPEAKER_STREAM_INTERFACE_INDEX, /* Speaker interfaces in the Audio Interface baNumber is 0x02 */

/******************* AC Specific type of Input Terminal:0x24 0x02*************************/

USB_AUDIO_INPUT_TERMINAL_ONLY_DESC_SIZE, /* Size of the descriptor, in bytes */

USB_DESCRIPTOR_TYPE_AUDIO_CS_INTERFACE, /* CS_INTERFACE Descriptor Type */

USB_DESCRIPTOR_SUBTYPE_AUDIO_CONTROL_INPUT_TERMINAL,

/* INPUT_TERMINAL descriptor subtype */

USB_AUDIO_RECORDER_CONTROL_INPUT_TERMINAL_ID, /* Constant uniquely identifying the Terminal within the audio

function. This value is used in all requests

to address this Terminal. */

0x01U, 0x02, /* A generic microphone that does not fit under any of the other classifications. */

0x00U, /* This Input Terminal has no association */

0x02U, /* This Terminal's output audio channel cluster has 1 logical output channels */

0x03U, 0x00U, /* Spatial locations present in the cluster */

0x00U, /* Index of a string descriptor, describing the name of the first logical channel. */

0x00U, /* Index of a string descriptor, describing the Input Terminal. */

/*******************Audio Class Specific type of Feature Unit:0x24 0x06*************************/

USB_AUDIO_FEATURE_UNIT_ONLY_DESC_SIZE(2, 1), /* Size of the descriptor, in bytes */

USB_DESCRIPTOR_TYPE_AUDIO_CS_INTERFACE, /* CS_INTERFACE Descriptor Type */

USB_DESCRIPTOR_SUBTYPE_AUDIO_CONTROL_FEATURE_UNIT, /* FEATURE_UNIT descriptor subtype */

USB_AUDIO_RECORDER_CONTROL_FEATURE_UNIT_ID, /* Constant uniquely identifying the Unit within the audio function.

This value is used in all requests to

address this Unit. */

USB_AUDIO_RECORDER_CONTROL_INPUT_TERMINAL_ID, /* ID of the Unit or Terminal to which this Feature Unit is connected.

0x01U, /* Size in bytes of an element of the bmaControls() array: */

0x01U, /* Master channel0: Mute */

0x02U, /* Left channel1: Volume*/

0x02U, /* Right channel2: Volume */

0x00U, /* Index of a string descriptor, describing this Feature Unit. */

/*******************Audio Class Specific type of Output Terminal:0x24 0x03*************************/

USB_AUDIO_OUTPUT_TERMINAL_ONLY_DESC_SIZE, /* Size of the descriptor, in bytes */

USB_DESCRIPTOR_TYPE_AUDIO_CS_INTERFACE, /* CS_INTERFACE Descriptor Type */

USB_DESCRIPTOR_SUBTYPE_AUDIO_CONTROL_OUTPUT_TERMINAL,

/* OUTPUT_TERMINAL descriptor subtype */

USB_AUDIO_RECORDER_CONTROL_OUTPUT_TERMINAL_ID, /* Constant uniquely identifying the Terminal within the audio

function*/

0x01U, 0x01U, /* A Terminal dealing with a signal carried over an endpoint in an AudioStreaming interface */

0x00U, /* This Output Terminal has no association */

USB_AUDIO_RECORDER_CONTROL_FEATURE_UNIT_ID, /* ID of the Unit or Terminal to which this Terminal is connected. */

0x00U, /* Index of a string descriptor, describing the Output Terminal. */

/******************* Audio Class Specific type of Input Terminal:0x24 0x02*************************/

USB_AUDIO_INPUT_TERMINAL_ONLY_DESC_SIZE, /* Size of the descriptor, in bytes */

USB_DESCRIPTOR_TYPE_AUDIO_CS_INTERFACE, /* CS_INTERFACE Descriptor Type */

USB_DESCRIPTOR_SUBTYPE_AUDIO_CONTROL_INPUT_TERMINAL,

/* INPUT_TERMINAL descriptor subtype */

USB_AUDIO_SPEAKER_CONTROL_INPUT_TERMINAL_ID, /* Constant uniquely identifying the Terminal within the audio

function. This value is used in all requests

to address this Terminal. */

0x01U, 0x01, /* A Terminal dealing with a signal carried over an endpoint in an AudioStreaming interface. */