USBAudio2DescriptorBuilder.h

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#include <cstdint>
#include <cstring>
#include <functional>
 
#include "tusb.h"
#include "USBAudioConfig.h"
 
 
namespace audio_tools {
 
// Audio 2.0 Descriptor Generator
class USBAudio2DescriptorBuilder {
 public:
  USBAudio2DescriptorBuilder(USBAudioConfig &cfg){
    p_config = &cfg;
  }
 
  uint16_t calcMaxPacketSize() const {
    uint16_t bytesPerFrame = (p_config->bits_per_sample / 8) * p_config->channels;
    uint16_t samplesPerMs = (p_config->sample_rate + 999) / 1000;
    return bytesPerFrame * samplesPerMs;
  }
 
  const uint8_t* buildDescriptor(uint8_t itf, uint8_t alt, uint16_t* outLen) {
    static uint8_t desc[256];
    uint8_t* p = desc;
 
    if (alt == 0) {
      p = addStandardInterfaceDesc(p, itf, alt, 0);
    } else {
      p = addStandardInterfaceDesc(p, itf, alt, 1);
      p = addCsInterfaceHeader(p);
      p = addInputTerminalDesc(p);
      p = addFeatureUnitDesc(p);
      p = addOutputTerminalDesc(p);
      p = addFormatTypeDesc(p);
      p = addIsoDataEndpointDesc(p);
      p = addCsIsoEndpointDesc(p);
    }
 
    *outLen = static_cast<uint16_t>(p - desc);
    return desc;
  }
 
 private:
  uint8_t* addStandardInterfaceDesc(uint8_t* p, uint8_t itf, uint8_t alt,
                                    uint8_t numEps) {
    *p++ = 9;       // bLength
    *p++ = 0x04;    // bDescriptorType = Interface
    *p++ = itf;     // bInterfaceNumber
    *p++ = alt;     // bAlternateSetting
    *p++ = numEps;  // bNumEndpoints
    *p++ = 0x01;    // bInterfaceClass (AUDIO)
    *p++ = 0x02;    // bInterfaceSubClass (Streaming)
    *p++ = 0x20;    // bInterfaceProtocol (2.0)
    *p++ = 0;       // iInterface
    return p;
  }
 
  uint8_t* addCsInterfaceHeader(uint8_t* p) {
    *p++ = 7;     // bLength
    *p++ = 0x24;  // CS_INTERFACE
    *p++ = 0x01;  // HEADER subtype
    *p++ = 0x00;
    *p++ = 0x02;  // bcdADC = 2.00
    *p++ = 0x01;  // bCategory = 1 (Speaker)
    *p++ = 0x00;  // wTotalLength (placeholder)
    return p;
  }
 
  uint8_t* addInputTerminalDesc(uint8_t* p) {
    *p++ = 17;                      // bLength
    *p++ = 0x24;                    // CS_INTERFACE
    *p++ = 0x02;                    // INPUT_TERMINAL subtype
    *p++ = p_config->entity_id_input_terminal;  // bTerminalID
    *p++ = 0x01;
    *p++ = 0x01;       // wTerminalType = USB Streaming
    *p++ = 0x00;       // bAssocTerminal
    *p++ = p_config->channels;  // bNrChannels
    *p++ = 0x03;
    *p++ = 0x00;
    *p++ = 0x00;
    *p++ = 0x00;  // wChannelConfig
    *p++ = 0;     // iChannelNames
    *p++ = 0;     // iTerminal
    return p;
  }
 
  uint8_t* addFeatureUnitDesc(uint8_t* p) {
    uint8_t length = 7 + (p_config->channels + 1) * 2;
    *p++ = length;                  // bLength
    *p++ = 0x24;                    // CS_INTERFACE
    *p++ = 0x06;                    // FEATURE_UNIT subtype
    *p++ = p_config->entity_id_feature_unit;    // bUnitID
    *p++ = p_config->entity_id_input_terminal;  // bSourceID
    *p++ = 0x01;                    // bControlSize
    *p++ = 0x01;                    // bmaControls[0] (Master Mute)
    for (uint8_t i = 1; i <= p_config->channels; ++i) {
      *p++ = 0x03;  // bmaControls[i] (Mute + Volume)
    }
    *p++ = 0x00;  // iFeature
    return p;
  }
 
  uint8_t* addOutputTerminalDesc(uint8_t* p) {
    *p++ = 12;                       // bLength
    *p++ = 0x24;                     // CS_INTERFACE
    *p++ = 0x03;                     // OUTPUT_TERMINAL subtype
    *p++ = p_config->entity_id_output_terminal;  // bTerminalID
    *p++ = 0x01;
    *p++ = 0x03;                  // wTerminalType = Speaker
    *p++ = 0x00;                  // bAssocTerminal
    *p++ = p_config->entity_id_feature_unit;  // bSourceID
    *p++ = 0x00;                  // iTerminal
    return p;
  }
 
  uint8_t* addFormatTypeDesc(uint8_t* p) {
    *p++ = 14;                  // bLength
    *p++ = 0x24;                // CS_INTERFACE
    *p++ = 0x02;                // FORMAT_TYPE subtype
    *p++ = 0x01;                // FORMAT_TYPE_I
    *p++ = p_config->channels;           // bNrChannels
    *p++ = p_config->bits_per_sample / 8;  // bSubslotSize
    *p++ = p_config->bits_per_sample;      // bBitResolution
    *p++ = 1;                   // bSamFreqType
    *p++ = (uint8_t)(p_config->sample_rate & 0xFF);
    *p++ = (uint8_t)((p_config->sample_rate >> 8) & 0xFF);
    *p++ = (uint8_t)((p_config->sample_rate >> 16) & 0xFF);
    return p;
  }
 
  uint8_t* addIsoDataEndpointDesc(uint8_t* p) {
    uint16_t packetSize = calcMaxPacketSize();
    *p++ = 7;                         // bLength
    *p++ = 0x05;                      // ENDPOINT descriptor
    *p++ = p_config->ep_in;                      // bEndpointAddress
    *p++ = 0x05;                      // bmAttributes (Isochronous, Async)
    *p++ = packetSize & 0xFF;         // wMaxPacketSize LSB
    *p++ = (packetSize >> 8) & 0xFF;  // wMaxPacketSize MSB
    *p++ = 0x01;                      // bInterval
    return p;
  }
 
  uint8_t* addCsIsoEndpointDesc(uint8_t* p) {
    *p++ = 8;     // bLength
    *p++ = 0x25;  // CS_ENDPOINT
    *p++ = 0x01;  // EP_GENERAL subtype
    *p++ = 0x00;  // bmAttributes
    *p++ = 0x00;  // bmControls
    *p++ = 0x00;
    *p++ = 0x00;  // wLockDelayUnits, wLockDelay
    return p;
  }
 
  USBAudioConfig *p_config = nullptr;
 
};
 
}  // namespace tinyusb