UAC2.0 描述符（二）

时间 2019-12-06

标签 uac2.0 uac 描述繁體版

原文原文链接

简单的UAC2.0设备的Audio Function Topology以下：git

Input Terminal Descriptor

下面描述了一个立体声的USB输入数据流的输入终端bash

AUDIO_20_IT_DESC_SIZE,                /* bLength */
  AUDIO_INTERFACE_DESCRIPTOR_TYPE,      /* bDescriptorType */
  AUDIO_CONTROL_INPUT_TERMINAL,         /* bDescriptorSubtype */
  AUDIO_IT_ID,                          /* bTerminalID */
  0x01,                                 /* wTerminalType AUDIO_TERMINAL_USB_STREAMING   0x0101 */
  0x01,
  0x00,                                 /* bAssocTerminal */
  AUDIO_CLK_ID,                         /* bCSourceID*/
  0x02,                                 /* bNrChannels */
  0x03,                                 /* wChannelConfig 0x00000003  Stereo */
  0x00,
  0x00,
  0x00,
  0x00,                                 /* iChannelNames */
  0x00,                                 /* bmControls */
  0x00,
  0x00,                                 /* iTerminal */

Feature Unit Descriptor

主通道支持音量和mute控制.net

0x12,                                 /* bLength */
  AUDIO_INTERFACE_DESCRIPTOR_TYPE,      /* bDescriptorType */
  AUDIO_CONTROL_FEATURE_UNIT,           /* bDescriptorSubtype */
  AUDIO_FU_ID,                          /* bUnitID */
  AUDIO_IT_ID,                          /* bSourceID */
  AUDIO_20_CTL_MUTE(CONTROL_BITMAP_PROG)/* bmaControls(0) */
  | AUDIO_20_CTL_VOLUME(CONTROL_BITMAP_PROG),
  0x00,
  0x00,
  0x00,
  0x00,                                 /* bmaControls(1) */
  0x00,
  0x00,
  0x00,
  0x00,                                 /* bmaControls(2) */
  0x00,
  0x00,
  0x00,
  0x00,                                 /* iFeature */

Output Terminal Descriptor

这里有个细节，若是OT的wTerminalType为0x0101(即USB Streaming)，在Mac OSX 10.12.5上是没法进行音量控制的code

AUDIO_20_OT_DESC_SIZE,      			/* bLength */
  AUDIO_INTERFACE_DESCRIPTOR_TYPE,      /* bDescriptorType */
  AUDIO_CONTROL_OUTPUT_TERMINAL,        /* bDescriptorSubtype */
  AUDIO_OT_ID,                          /* bTerminalID */
  0x02,                                 /* wTerminalType  0x0301: Speaker, 0x0302: Headphone*/
  0x03,
  0x00,                                 /* bAssocTerminal */
  AUDIO_FU_ID,                          /* bSourceID */
  AUDIO_CLK_ID,                         /* bCSourceID */
  0x00,                                 /* bmControls */
  0x00,
  0x00,                                 /* iTerminal */

Clock Source Descriptor

时钟域的概念是UAC2.0里新提出的，经过时钟域的改变进行采样率的更新。ip

AUDIO_20_CLK_SOURCE_DESC_SIZE,        /* bLength */
  AUDIO_INTERFACE_DESCRIPTOR_TYPE,      /* bDescriptorType */
  AUDIO_CONTROL_CLOCK_SOURCE,           /* bDescriptorSubtype */
  AUDIO_CLK_ID,                         /* bClockID */
  0x01,                                 /* bmAttributes */
  0x07,                                 /* bmControls TODO */
  0x00,                                 /* bAssocTerminal */
  0x00,                                 /* iClockSource */

细节可参考我基于STM32F4Discovery实现了一个简单的UAC2.0设备（https://git.oschina.net/crouchggj/STM32F4_USB_SoundCard.git）。get