Usb failed packets

Which one of these should I be changing the feild bInterval and bRefresh for. If you could explain how they both work together would help.

/* Endpoint - Standard Descriptor */
  AUDIO_STANDARD_ENDPOINT_DESC_SIZE,    /* bLength */
  USB_ENDPOINT_DESCRIPTOR_TYPE,         /* bDescriptorType */
  USB_ENDPOINT_OUT(3),                  /* bEndpointAddress */
  USB_ENDPOINT_TYPE_ISOCHRONOUS | USB_ENDPOINT_SYNC_ASYNCHRONOUS,        /* bmAttributes */          // <-------
  WBVAL(66),                            /* wMaxPacketSize */   // <-------
  0x01,                                 /* bInterval */
  0x00,                                 /* bRefresh */
  0x83,                                 /* bSynchAddress */    // <-------

/* Endpoint - Standard Descriptor - for feedback */
  AUDIO_STANDARD_ENDPOINT_DESC_SIZE,    /* bLength */
  USB_ENDPOINT_DESCRIPTOR_TYPE,         /* bDescriptorType */
  USB_ENDPOINT_IN(3),                   /* bEndpointAddress */
  USB_ENDPOINT_TYPE_ISOCHRONOUS,        /* bmAttributes */
  WBVAL(3),                             /* wMaxPacketSize */
  0x01,                                 /* bInterval */
  0x01,                                 /* bRefresh */
  0x00,                                 /* bSynchAddress */

If I set them like this

/* Endpoint - Standard Descriptor */
  AUDIO_STANDARD_ENDPOINT_DESC_SIZE,    /* bLength */
  USB_ENDPOINT_DESCRIPTOR_TYPE,         /* bDescriptorType */
  USB_ENDPOINT_OUT(3),                  /* bEndpointAddress */
  USB_ENDPOINT_TYPE_ISOCHRONOUS | USB_ENDPOINT_SYNC_ASYNCHRONOUS,        /* bmAttributes */          // <-------
  WBVAL(66),                            /* wMaxPacketSize */   // <-------
  0x01,                                 /* bInterval */   <------------------------ Interval for polling endpoint for data transfers expressed in milliseconds  0x01 = 1 packet every frame
  0x09,                                 /* bRefresh */   <----------------------------- 512ms until synchronization pipe provides new synchronization feedback data.
  0x83,                                 /* bSynchAddress */    // <-------

would that mean I would get 1ms delay for polling data transfers of 1 packet every frame, and then 512ms before the endpoint provides new synchronization feedback data.

what do you feel they should be set at.

What are you suggesting to be changed when you wrote these comments, are you talking about audio.h and desc.c WBVAL(66), and P_S Packet Size

2) Variable number of samples per frame
Async Sink results +/- 1 samples per frame occasionally, when the frequency ratio of
the local sampling clock and SOF is apart from an integer number.
But original Keil implementation assumes that the sample number per frame would be constant,
and this number is power of 2, ie. 1, 2, 4, 8, 16, 32,...
This assumption is fine for Adaptive/Synchronous Sink, but it is not approved for Async Sink.

/* Audio Definitions */
#define DATA_FREQ 32000                 /* Audio Data Frequency */
#define P_S       32                    /* Packet Size */
#if USB_DMA
#define P_C       4                     /* Packet Count */
#else
#define P_C       1                     /* Packet Count */
#endif
#define B_S       (8*P_C*P_S)           /* Buffer Size */

>> The mods on above post has to be modified more for variable transferred data size on each frame.

Could you give me details about what I am to do here

> Do you know why

I don't know :-)
There aren't so many differences between MCB1700 and OLIMEX_LPC1766STK for this example.
Just the analog port, to which a pod connects.
I put the #define into the source, to cover this difference.

a) Is the original Keil example runs on your MCB1700?
b) What is the version of Windows?
c) How doesn't it "work"? Is it enumerated? No sound?, etc

Tsuneo

Could you answer these comments first please. Much more important to me than getting the code you posted to work thankyou.

Which one of these should I be changing the feild bInterval and bRefresh for. If you could explain how they both work together would help.

/* Endpoint - Standard Descriptor */
  AUDIO_STANDARD_ENDPOINT_DESC_SIZE,    /* bLength */
  USB_ENDPOINT_DESCRIPTOR_TYPE,         /* bDescriptorType */
  USB_ENDPOINT_OUT(3),                  /* bEndpointAddress */
  USB_ENDPOINT_TYPE_ISOCHRONOUS | USB_ENDPOINT_SYNC_ASYNCHRONOUS,        /* bmAttributes */          // <-------
  WBVAL(66),                            /* wMaxPacketSize */   // <-------
  0x01,                                 /* bInterval */
  0x00,                                 /* bRefresh */
  0x83,                                 /* bSynchAddress */    // <-------

/* Endpoint - Standard Descriptor - for feedback */
  AUDIO_STANDARD_ENDPOINT_DESC_SIZE,    /* bLength */
  USB_ENDPOINT_DESCRIPTOR_TYPE,         /* bDescriptorType */
  USB_ENDPOINT_IN(3),                   /* bEndpointAddress */
  USB_ENDPOINT_TYPE_ISOCHRONOUS,        /* bmAttributes */
  WBVAL(3),                             /* wMaxPacketSize */
  0x01,                                 /* bInterval */
  0x01,                                 /* bRefresh */
  0x00,                                 /* bSynchAddress */

If I set them like this

/* Endpoint - Standard Descriptor */
  AUDIO_STANDARD_ENDPOINT_DESC_SIZE,    /* bLength */
  USB_ENDPOINT_DESCRIPTOR_TYPE,         /* bDescriptorType */
  USB_ENDPOINT_OUT(3),                  /* bEndpointAddress */
  USB_ENDPOINT_TYPE_ISOCHRONOUS | USB_ENDPOINT_SYNC_ASYNCHRONOUS,        /* bmAttributes */          // <-------
  WBVAL(66),                            /* wMaxPacketSize */   // <-------
  0x01,                                 /* bInterval */   <------------------------ Interval for polling endpoint for data transfers expressed in milliseconds  0x01 = 1 packet every frame
  0x09,                                 /* bRefresh */   <----------------------------- 512ms until synchronization pipe provides new synchronization feedback data.
  0x83,                                 /* bSynchAddress */    // <-------

would that mean I would get 1ms delay for polling data transfers of 1 packet every frame, and then 512ms before the endpoint provides new synchronization feedback data.

what do you feel they should be set at.

What are you suggesting to be changed when you wrote these comments, are you talking about audio.h and desc.c WBVAL(66), and P_S Packet Size

2) Variable number of samples per frame
Async Sink results +/- 1 samples per frame occasionally, when the frequency ratio of
the local sampling clock and SOF is apart from an integer number.
But original Keil implementation assumes that the sample number per frame would be constant,
and this number is power of 2, ie. 1, 2, 4, 8, 16, 32,...
This assumption is fine for Adaptive/Synchronous Sink, but it is not approved for Async Sink.

/* Audio Definitions */
#define DATA_FREQ 32000                 /* Audio Data Frequency */
#define P_S       32                    /* Packet Size */
#if USB_DMA
#define P_C       4                     /* Packet Count */
#else
#define P_C       1                     /* Packet Count */
#endif
#define B_S       (8*P_C*P_S)           /* Buffer Size */

>> The mods on above post has to be modified more for variable transferred data size on each frame.

Could you give me details about what I am to do here

1) Feedback refresh interval
> Which one of these should I be changing the feild bInterval and bRefresh for.

Both of bInterval fields of the OUT and IN endpoints are set to 1 (ms)
I mean the bRefresh field of the feedback IN EP.

Host (Windows and Mac) polls the feedback IN endpoint in the interval specified by the bRefresh value, not in 1ms interval.
USB Audio spec tells the shortest interval is 2 ms (bRefresh = 1)
But there seems lower limit by OS audio driver implementation,
MacOSX: 8 ms (bRefresh = 3), and Windows: 11 or 12 ms

In above implementation, the firmware calculates the feedback value on every SOF interrupt.
We have to change this behavior.
When bRefresh = 3, the firmware calculate feedback value in every 8 ms.

#define FEEDBACK_REFRESH_EXPONENT  3      // bRefresh value for the feedback IN EP (1..9)
#define FEEDBACK_REFRESH_INTERVAL  (1 << FEEDBACK_REFRESH_EXPONENT)

uint8_t feedback_refresh_timer = FEEDBACK_REFRESH_INTERVAL;
uint32_t last_timer_count;
extern uint32_t sampling_interval;

#if USB_SOF_EVENT
void USB_SOF_Event (void) {

  uint32_t current_timer_count;
  uint32_t feedback_value;
                                                // feedback
  current_timer_count = LPC_TIM1->TC;           // capture current SOF timing on the Timer1
  if ( --feedback_refresh_timer == 0 ) {

    if ( USB_AltSetting[1] == 1 ) {             // When interface 1 / alt 1 is enabled,
                                                // calculate master/SOF frequency ratio in 10.10 (10.14) format
      feedback_value = ((current_timer_count - last_timer_count) << 14) / FEEDBACK_REFRESH_INTERVAL / sampling_interval;
                                                // and send it to the feedback IN EP
      USB_WriteEP( 0x83, (uint8_t*)&feedback_value, 3 );
    }
    last_timer_count = current_timer_count;     // update the last SOF timing
    feedback_refresh_timer = FEEDBACK_REFRESH_INTERVAL;
  }

WBVAL(66) (wMaxPacketSize of isoc OUT EP)

The original example sets this value to WBVAL(64), ie. 32 samples for 32kHz monaural 16bits.
But MacOSX doesn't put any feedback IN transaction for this value.
To receive feedback IN transactions, at least WBVAL(66) (32 + 1 samples) is required.

2) Variable number of samples per frame

This modification is required not just for Async Sink, but also for support of fractional sampling rate, such as 44.1kHz

For DMA implementation of the isoc OUT EP,
USB_EndPoint3() is called when packet counts (P_C) number of packets are received.
Packet Info Buffer (InfoBuf array) holds received size of each packets (LSB 2 bytes)
(refer to "11.15.6 Isochronous endpoint operation" of the LPC17xx manual)

For slave implementation of the isoc OUT EP, USB_ReadEP() in USB_SOF_Event() returns received packet size.

In these callbacks (DMA:USB_EndPoint3(), slave:USB_SOF_Event())
DataIn index increments by actual received packet size, instead of the constant value (P_C*P_S or P_S) of the original.
A problem lies in the end of the cyclic buffer. It moves around by the extra (or less) sample(s).
When DataIn reaches near the end of the cyclic buffer, this index is held in a current_end_of_buffer variable.
And DataIn wraparounds to the top of the buffer.

In the playback routine (TIMER0_IRQHandler()),
DataOut wraparounds to the top of the buffer, when it reaches to above current_end_of_buffer.

Tsuneo

its a bug with

sync Reset Pipe and Clear Stall, do you know how to fix

After searching the internet, the best I have come with is that, it could have something to do
with usb.h and adcuser.c

in windows 7 every 50 to 80 us SYNC_RESET_PIPE_AND_CLEAR_STALL is being issued and failing causing lost packets and out of sync audio packets

The _URB_PIPE_REQUEST structure is used by USB client drivers to clear a stall condition on an endpoint.
Syntax
struct _URB_PIPE_REQUEST { struct URB_HEADER Hdr; USBD_PIPE_HANDLE PipeHandle; ULONG Reserved;
};
Members
Hdr
Pointer to the _URB_HEADER structure that specifies the URB header information. Hdr.Function must be one of the following:
URB_FUNCTION_SYNC_RESET_PIPE_AND_CLEAR_STALL
URB_FUNCTION_SYNC_RESET_PIPE
URB_FUNCTION_SYNC_CLEAR_STALL
URB_FUNCTION_ABORT_PIPE
URB_FUNCTION_CLOSE_STATIC_STREAMS
The Hdr.Length member must be sizeof(_URB_PIPE_REQUEST).
PipeHandle
Specifies an opaque handle to the bulk or interrupt pipe. The host controller driver returns this handle when the client driver selects the device configuration with a URB of type URB_FUNCTION_SELECT_CONFIGURATION or when the client driver changes the settings for an interface with a URB of type URB_FUNCTION_SELECT_INTERFACE.
Reserved
Reserved. Do not use.
Remarks
The reserved members of this structure must be treated as opaque and are reserved for system use.
Requirements
Header
Usb.h (include Usb.h)

/*----------------------------------------------------------------------------
 *      U S B  -  K e r n e l
 *----------------------------------------------------------------------------
 * Name:    usb.h
 * Purpose: USB Definitions
 * Version: V1.20
 *----------------------------------------------------------------------------
 *      This software is supplied "AS IS" without any warranties, express,
 *      implied or statutory, including but not limited to the implied
 *      warranties of fitness for purpose, satisfactory quality and
 *      noninfringement. Keil extends you a royalty-free right to reproduce
 *      and distribute executable files created using this software for use
 *      on NXP Semiconductors LPC family microcontroller devices only. Nothing
 *      else gives you the right to use this software.
 *
 * Copyright (c) 2009 Keil - An ARM Company. All rights reserved.
 *---------------------------------------------------------------------------*/

#ifndef __USB_H__
#define __USB_H__


typedef __packed union {
  uint16_t W;
  __packed struct {
    uint8_t L;
    uint8_t H;
  } WB;
} WORD_BYTE;


/* bmRequestType.Dir */
#define REQUEST_HOST_TO_DEVICE     0
#define REQUEST_DEVICE_TO_HOST     1

/* bmRequestType.Type */
#define REQUEST_STANDARD           0
#define REQUEST_CLASS              1
#define REQUEST_VENDOR             2
#define REQUEST_RESERVED           3

/* bmRequestType.Recipient */
#define REQUEST_TO_DEVICE          0
#define REQUEST_TO_INTERFACE       1
#define REQUEST_TO_ENDPOINT        2
#define REQUEST_TO_OTHER           3

/* bmRequestType Definition */
typedef __packed union _REQUEST_TYPE {
  __packed struct _BM {
    uint8_t Recipient : 5;
    uint8_t Type      : 2;
    uint8_t Dir       : 1;
  } BM;
  uint8_t B;
} REQUEST_TYPE;

/* USB Standard Request Codes */
#define USB_REQUEST_GET_STATUS                 0
#define USB_REQUEST_CLEAR_FEATURE              1
#define USB_REQUEST_SET_FEATURE                3
#define USB_REQUEST_SET_ADDRESS                5
#define USB_REQUEST_GET_DESCRIPTOR             6
#define USB_REQUEST_SET_DESCRIPTOR             7
#define USB_REQUEST_GET_CONFIGURATION          8
#define USB_REQUEST_SET_CONFIGURATION          9
#define USB_REQUEST_GET_INTERFACE              10
#define USB_REQUEST_SET_INTERFACE              11
#define USB_REQUEST_SYNC_FRAME                 12

/* USB GET_STATUS Bit Values */
#define USB_GETSTATUS_SELF_POWERED             0x01
#define USB_GETSTATUS_REMOTE_WAKEUP            0x02
#define USB_GETSTATUS_ENDPOINT_STALL           0x01

/* USB Standard Feature selectors */
#define USB_FEATURE_ENDPOINT_STALL             0
#define USB_FEATURE_REMOTE_WAKEUP              1

/* USB Default Control Pipe Setup Packet */
typedef __packed struct _USB_SETUP_PACKET {
  REQUEST_TYPE bmRequestType;
  uint8_t         bRequest;
  WORD_BYTE    wValue;
  WORD_BYTE    wIndex;
  uint16_t         wLength;
} USB_SETUP_PACKET;


/* USB Descriptor Types */
#define USB_DEVICE_DESCRIPTOR_TYPE                  1
#define USB_CONFIGURATION_DESCRIPTOR_TYPE           2
#define USB_STRING_DESCRIPTOR_TYPE                  3
#define USB_INTERFACE_DESCRIPTOR_TYPE               4
#define USB_ENDPOINT_DESCRIPTOR_TYPE                5
#define USB_DEVICE_QUALIFIER_DESCRIPTOR_TYPE        6
#define USB_OTHER_SPEED_CONFIG_DESCRIPTOR_TYPE      7
#define USB_INTERFACE_POWER_DESCRIPTOR_TYPE         8
#define USB_OTG_DESCRIPTOR_TYPE                     9
#define USB_DEBUG_DESCRIPTOR_TYPE                  10
#define USB_INTERFACE_ASSOCIATION_DESCRIPTOR_TYPE  11

/* USB Device Classes */
#define USB_DEVICE_CLASS_RESERVED              0x00
#define USB_DEVICE_CLASS_AUDIO                 0x01
#define USB_DEVICE_CLASS_COMMUNICATIONS        0x02
#define USB_DEVICE_CLASS_HUMAN_INTERFACE       0x03
#define USB_DEVICE_CLASS_MONITOR               0x04
#define USB_DEVICE_CLASS_PHYSICAL_INTERFACE    0x05
#define USB_DEVICE_CLASS_POWER                 0x06
#define USB_DEVICE_CLASS_PRINTER               0x07
#define USB_DEVICE_CLASS_STORAGE               0x08
#define USB_DEVICE_CLASS_HUB                   0x09
#define USB_DEVICE_CLASS_MISCELLANEOUS         0xEF
#define USB_DEVICE_CLASS_VENDOR_SPECIFIC       0xFF

/* bmAttributes in Configuration Descriptor */
#define USB_CONFIG_POWERED_MASK                0x40
#define USB_CONFIG_BUS_POWERED                 0x80
#define USB_CONFIG_SELF_POWERED                0xC0
#define USB_CONFIG_REMOTE_WAKEUP               0x20

/* bMaxPower in Configuration Descriptor */
#define USB_CONFIG_POWER_MA(mA)                ((mA)/2)

/* bEndpointAddress in Endpoint Descriptor */
#define USB_ENDPOINT_DIRECTION_MASK            0x80
#define USB_ENDPOINT_OUT(addr)                 ((addr) | 0x00)
#define USB_ENDPOINT_IN(addr)                  ((addr) | 0x80)

/* bmAttributes in Endpoint Descriptor */
#define USB_ENDPOINT_TYPE_MASK                 0x03
#define USB_ENDPOINT_TYPE_CONTROL              0x00
#define USB_ENDPOINT_TYPE_ISOCHRONOUS          0x01
#define USB_ENDPOINT_TYPE_BULK                 0x02
#define USB_ENDPOINT_TYPE_INTERRUPT            0x03
#define USB_ENDPOINT_SYNC_MASK                 0x0C
#define USB_ENDPOINT_SYNC_NO_SYNCHRONIZATION   0x00
#define USB_ENDPOINT_SYNC_ASYNCHRONOUS         0x04
#define USB_ENDPOINT_SYNC_ADAPTIVE             0x08
#define USB_ENDPOINT_SYNC_SYNCHRONOUS          0x0C
#define USB_ENDPOINT_USAGE_MASK                0x30
#define USB_ENDPOINT_USAGE_DATA                0x00
#define USB_ENDPOINT_USAGE_FEEDBACK            0x10
#define USB_ENDPOINT_USAGE_IMPLICIT_FEEDBACK   0x20
#define USB_ENDPOINT_USAGE_RESERVED            0x30

/* USB Standard Device Descriptor */
typedef __packed struct _USB_DEVICE_DESCRIPTOR {
  uint8_t  bLength;
  uint8_t  bDescriptorType;
  uint16_t  bcdUSB;
  uint8_t  bDeviceClass;
  uint8_t  bDeviceSubClass;
  uint8_t  bDeviceProtocol;
  uint8_t  bMaxPacketSize0;
  uint16_t  idVendor;
  uint16_t  idProduct;
  uint16_t  bcdDevice;
  uint8_t  iManufacturer;
  uint8_t  iProduct;
  uint8_t  iSerialNumber;
  uint8_t  bNumConfigurations;
} USB_DEVICE_DESCRIPTOR;

/* USB 2.0 Device Qualifier Descriptor */
typedef __packed struct _USB_DEVICE_QUALIFIER_DESCRIPTOR {
  uint8_t  bLength;
  uint8_t  bDescriptorType;
  uint16_t  bcdUSB;
  uint8_t  bDeviceClass;
  uint8_t  bDeviceSubClass;
  uint8_t  bDeviceProtocol;
  uint8_t  bMaxPacketSize0;
  uint8_t  bNumConfigurations;
  uint8_t  bReserved;
} USB_DEVICE_QUALIFIER_DESCRIPTOR;

/* USB Standard Configuration Descriptor */
typedef __packed struct _USB_CONFIGURATION_DESCRIPTOR {
  uint8_t  bLength;
  uint8_t  bDescriptorType;
  uint16_t  wTotalLength;
  uint8_t  bNumInterfaces;
  uint8_t  bConfigurationValue;
  uint8_t  iConfiguration;
  uint8_t  bmAttributes;
  uint8_t  bMaxPower;
} USB_CONFIGURATION_DESCRIPTOR;

/* USB Standard Interface Descriptor */
typedef __packed struct _USB_INTERFACE_DESCRIPTOR {
  uint8_t  bLength;
  uint8_t  bDescriptorType;
  uint8_t  bInterfaceNumber;
  uint8_t  bAlternateSetting;
  uint8_t  bNumEndpoints;
  uint8_t  bInterfaceClass;
  uint8_t  bInterfaceSubClass;
  uint8_t  bInterfaceProtocol;
  uint8_t  iInterface;
} USB_INTERFACE_DESCRIPTOR;

/* USB Standard Endpoint Descriptor */
typedef __packed struct _USB_ENDPOINT_DESCRIPTOR {
  uint8_t  bLength;
  uint8_t  bDescriptorType;
  uint8_t  bEndpointAddress;
  uint8_t  bmAttributes;
  uint16_t  wMaxPacketSize;
  uint8_t  bInterval;
} USB_ENDPOINT_DESCRIPTOR;

/* USB String Descriptor */
typedef __packed struct _USB_STRING_DESCRIPTOR {
  uint8_t  bLength;
  uint8_t  bDescriptorType;
  uint16_t  bString/*[]*/;
} USB_STRING_DESCRIPTOR;

/* USB Common Descriptor */
typedef __packed struct _USB_COMMON_DESCRIPTOR {
  uint8_t  bLength;
  uint8_t  bDescriptorType;
} USB_COMMON_DESCRIPTOR;


#endif  /* __USB_H__ */

/*----------------------------------------------------------------------------
 *      U S B  -  K e r n e l
 *----------------------------------------------------------------------------
 *      Name:    ADCUSER.C
 *      Purpose: Audio Device Class Custom User Module
 *      Version: V1.10
 *----------------------------------------------------------------------------
 *      This software is supplied "AS IS" without any warranties, express,
 *      implied or statutory, including but not limited to the implied
 *      warranties of fitness for purpose, satisfactory quality and
 *      noninfringement. Keil extends you a royalty-free right to reproduce
 *      and distribute executable files created using this software for use
 *      on NXP Semiconductors LPC family microcontroller devices only. Nothing
 *      else gives you the right to use this software.
 *
 * Copyright (c) 2009 Keil - An ARM Company. All rights reserved.
 *---------------------------------------------------------------------------*/

#include "type.h"

#include "usb.h"
#include "audio.h"
#include "usbcfg.h"
#include "usbcore.h"
#include "adcuser.h"

#include "usbaudio.h"

      uint16_t VolCur = 0x0100;     /* Volume Current Value */
const uint16_t VolMin = 0x0000;     /* Volume Minimum Value */
const uint16_t VolMax = 0x0100;     /* Volume Maximum Value */
const uint16_t VolRes = 0x0004;     /* Volume Resolution */

/*
 *  Audio Device Class Interface Get Request Callback
 *   Called automatically on ADC Interface Get Request
 *    Parameters:      None (global SetupPacket and EP0Buf)
 *    Return Value:    TRUE - Success, FALSE - Error
 */

uint32_t ADC_IF_GetRequest (void) {

/*
  Interface = SetupPacket.wIndex.WB.L;
  EntityID  = SetupPacket.wIndex.WB.H;
  Request   = SetupPacket.bRequest;
  Value     = SetupPacket.wValue.W;
  ...
*/

  if (SetupPacket.wIndex.W == 0x0200) {
    /* Feature Unit: Interface = 0, ID = 2 */
    if (SetupPacket.wValue.WB.L == 0) {
      /* Master Channel */
      switch (SetupPacket.wValue.WB.H) {
        case AUDIO_MUTE_CONTROL:
          switch (SetupPacket.bRequest) {
            case AUDIO_REQUEST_GET_CUR:
              EP0Buf[0] = Mute;
              return (TRUE);
          }
          break;
        case AUDIO_VOLUME_CONTROL:
          switch (SetupPacket.bRequest) {
            case AUDIO_REQUEST_GET_CUR:
              *((__packed uint16_t *)EP0Buf) = VolCur;
              return (TRUE);
            case AUDIO_REQUEST_GET_MIN:
              *((__packed uint16_t *)EP0Buf) = VolMin;
              return (TRUE);
            case AUDIO_REQUEST_GET_MAX:
              *((__packed uint16_t *)EP0Buf) = VolMax;
              return (TRUE);
            case AUDIO_REQUEST_GET_RES:
              *((__packed uint16_t *)EP0Buf) = VolRes;
              return (TRUE);
          }
          break;
      }
    }
  }
  return (FALSE);  /* Not Supported */
}


/*
 *  Audio Device Class Interface Set Request Callback
 *   Called automatically on ADC Interface Set Request
 *    Parameters:      None (global SetupPacket and EP0Buf)
 *    Return Value:    TRUE - Success, FALSE - Error
 */

uint32_t ADC_IF_SetRequest (void) {

/*
  Interface = SetupPacket.wIndex.WB.L;
  EntityID  = SetupPacket.wIndex.WB.H;
  Request   = SetupPacket.bRequest;
  Value     = SetupPacket.wValue.W;
  ...
*/

  if (SetupPacket.wIndex.W == 0x0200) {
    /* Feature Unit: Interface = 0, ID = 2 */
    if (SetupPacket.wValue.WB.L == 0) {
      /* Master Channel */
      switch (SetupPacket.wValue.WB.H) {
        case AUDIO_MUTE_CONTROL:
          switch (SetupPacket.bRequest) {
            case AUDIO_REQUEST_SET_CUR:
              Mute = EP0Buf[0];
              return (TRUE);
          }
          break;
        case AUDIO_VOLUME_CONTROL:
          switch (SetupPacket.bRequest) {
            case AUDIO_REQUEST_SET_CUR:
              VolCur = *((__packed uint16_t *)EP0Buf);
              return (TRUE);
          }
          break;
      }
    }
  }
  return (FALSE);  /* Not Supported */
}


/*
 *  Audio Device Class EndPoint Get Request Callback
 *   Called automatically on ADC EndPoint Get Request
 *    Parameters:      None (global SetupPacket and EP0Buf)
 *    Return Value:    TRUE - Success, FALSE - Error
 */

uint32_t ADC_EP_GetRequest (void) {

/*
  EndPoint = SetupPacket.wIndex.WB.L;
  Request  = SetupPacket.bRequest;
  Value    = SetupPacket.wValue.W;
  ...
*/
  return (FALSE);  /* Not Supported */
}


/*
 *  Audio Device Class EndPoint Set Request Callback
 *   Called automatically on ADC EndPoint Set Request
 *    Parameters:      None (global SetupPacket and EP0Buf)
 *    Return Value:    TRUE - Success, FALSE - Error
 */

uint32_t ADC_EP_SetRequest (void) {

/*
  EndPoint = SetupPacket.wIndex.WB.L;
  Request  = SetupPacket.bRequest;
  Value    = SetupPacket.wValue.W;
  ...
*/
  return (FALSE);  /* Not Supported */
}

After searching the internet, the best I have come with is that, it could have something to do
with usb.h and adcuser.c

in windows 7 every 50 to 80 us SYNC_RESET_PIPE_AND_CLEAR_STALL is being issued and failing causing lost packets and out of sequence audio packets

case URB_FUNCTION_SYNC_CLEAR_STALL and case case URB_FUNCTION_SYNC_RESET_PIPE. These allow client drivers to clear the ENDPOINT_HALT feature on the device, or reset the pipe on the host side, respectively, without affecting the data toggle on the host side. If the device does not reset the data toggle when it should, then the client driver can compensate for this defect by not resetting the host-side data toggle.

If the data toggle is reset on the host side but not on the device side, packets will get out of sequence, and the device might drop packets

???????