====== USB Audio Call Tree ======
----
===== USB_Istr =====

  USB_Istr <-- USB_LP_CAN1_RX0_IRQHandler
  |   CTR_LP
  |   |   In0_Process
  |   |   Setup0_Process
  |   |   Out0_Process
  |   |   (*pEpInt_OUT[EPindex-1])() -- Callback
  |   |   |   EP1_OUT_Callback
  |   |   |   |   GetENDPOINT
  |   |   |   |   GetEPDblBuf0Count
  |   |   |   |   GetEPDblBuf1Count
  |   |   |   |   PMAToUserBufferCopy
  |   |   |   EP2_OUT_Callback
  |   |   |   EP3_OUT_Callback
  |   |   |   EP4_OUT_Callback
  |   |   |   EP5_OUT_Callback
  |   |   |   EP6_OUT_Callback
  |   |   |   EP7_OUT_Callback
  |   |   (*pEpInt_IN[EPindex-1])()
  |   |   |   EP1_IN_Callback
  |   |   |   EP2_IN_Callback
  |   |   |   EP3_IN_Callback
  |   |   |   EP4_IN_Callback
  |   |   |   EP5_IN_Callback
  |   |   |   EP6_IN_Callback
  |   |   |   EP7_IN_Callback            
  |   Speaker_Reset -- Callback
  
  
==== Setup0_Process ====

  Setup0_Process
  |    NoData_Setup0
  |    |    Standard_SetConfiguration
  |    |    Standard_SetDeviceFeature
  |    |    Standard_ClearFeature
  |    |    Standard_SetInterface
  |    |    |    Speaker_Get_Interface_Setting - **Callback** via Class_Get_Interface_Setting
  |    |    |    Speaker_SetInterface - **Callback** via User_SetInterface
  |    |    Standard_ClearFeature
  |    |    Standard_SetEndPointFeature
  |    |    Class_NoData_Setup
  |    |    USB_StatusIn
  |    Data_Setup0  
  |    Post0_Process
  
  
==== USB_HP_CAN1_TX_IRQHandler/USB_HP_IRQHandler ====
  USB_HP_CAN1_TX_IRQHandler / USB_HP_IRQHandler
  |    CTR_HP();
  |   |   (*pEpInt_OUT[EPindex-1])() -- Callback
  |   |   |   EP1_OUT_Callback
  |   |   |   |   GetENDPOINT
  |   |   |   |   GetEPDblBuf0Count
  |   |   |   |   GetEPDblBuf1Count
  |   |   |   |   PMAToUserBufferCopy
  |   |   |   EP2_OUT_Callback
  |   |   |   EP3_OUT_Callback
  |   |   |   EP4_OUT_Callback
  |   |   |   EP5_OUT_Callback
  |   |   |   EP6_OUT_Callback
  |   |   |   EP7_OUT_Callback
  |   |   (*pEpInt_IN[EPindex-1])()
  |   |   |   EP1_IN_Callback
  |   |   |   EP2_IN_Callback
  |   |   |   EP3_IN_Callback
  |   |   |   EP4_IN_Callback
  |   |   |   EP5_IN_Callback
  |   |   |   EP6_IN_Callback
  |   |   |   EP7_IN_Callback          
   
 ===== USB_Init =====       
  USB_Init
  |    Speaker_init - Callback
  |    |    Get_SerialNum
  |    |    PowerOn
  |    |    |    USB_Cable_Config
  |    |    USB_SIL_Init
  |    |    |  _SetISTR
  |    |    |  _SetCNTR

===== APIs =====
----
==== usb_regs ====
The usb_regs module implements the hardware abstraction layer, it offers a set of basic
functions for accessing the USB-FS_Device **peripheral registers**.

^  Common register functions  ^^
^ Register  ^ Function                          ^
| CNTR      | void SetCNTR (uint16_t wValue)    |
| :::       | uint16_t GetCNTR (void)           |
| ISTR      | void SetISTR (uint16_t wValue)    |
| :::       | uint16_t GetISTR (void)           |
| FNR       | uint16_t GetFNR (void)            |
| DADDR     | void SetDADDR (uint16_t wValue)   |
| :::       | uint16_t GetDADDR (void)          |
| BTABLE    | void SetBTABLE (uint16_t wValue)  |
| :::       | uint16_t GetBTABLE (void)         |

==== Endpoint register functions ====
All operations with endpoint registers can be obtained with the SetENDPOINT and
GetENDPOINT functions. However, many functions are derived from these to offer the
advantage of a direct action on a specific field.