CDC in a composite device

A USB Composite Device is a USB Device which uses more than one USB class.

In this use case, the "USB CDC (Composite Device)" module is used to create a USB composite device. Thus, this USB module can be associated with another "Composite Device" module, like "USB HID Mouse (Composite Device)".

Also, you can refer to application note AVR4902 ASF - USB Composite Device.

Setup steps

For the setup code of this use case to work, the basic use case must be followed.

Usage steps

Example code

Content of conf_usb.h:

#define USB_DEVICE_EP_CTRL_SIZE  64
#define USB_DEVICE_NB_INTERFACE (X+2)
#define USB_DEVICE_MAX_EP (X+3)

#define  UDI_CDC_DATA_EP_IN_0          (1 | USB_EP_DIR_IN)  // TX
#define  UDI_CDC_DATA_EP_OUT_0         (2 | USB_EP_DIR_OUT) // RX
#define  UDI_CDC_COMM_EP_0             (3 | USB_EP_DIR_IN)  // Notify endpoint
#define  UDI_CDC_COMM_IFACE_NUMBER_0   X+0
#define  UDI_CDC_DATA_IFACE_NUMBER_0   X+1

#define UDI_COMPOSITE_DESC_T \
   usb_iad_desc_t udi_cdc_iad; \
   udi_cdc_comm_desc_t udi_cdc_comm; \
   udi_cdc_data_desc_t udi_cdc_data; \
   ...
#define UDI_COMPOSITE_DESC_FS \
   .udi_cdc_iad               = UDI_CDC_IAD_DESC_0, \
   .udi_cdc_comm              = UDI_CDC_COMM_DESC_0, \
   .udi_cdc_data              = UDI_CDC_DATA_DESC_0_FS, \
   ...
#define UDI_COMPOSITE_DESC_HS \
   .udi_cdc_iad               = UDI_CDC_IAD_DESC_0, \
   .udi_cdc_comm              = UDI_CDC_COMM_DESC_0, \
   .udi_cdc_data              = UDI_CDC_DATA_DESC_0_HS, \
   ...
#define UDI_COMPOSITE_API \
   &udi_api_cdc_comm,       \
   &udi_api_cdc_data,       \
   ...

Workflow

1. Ensure that conf_usb.h is available and contains the following parameters required for a USB composite device configuration:

   • // Endpoint control size, This must be:
        // - 8, 16, 32 or 64 for full speed device (8 is recommended to save RAM)
        // - 64 for a high speed device
        #define USB_DEVICE_EP_CTRL_SIZE  64
        // Total Number of interfaces on this USB device.
        // Add 2 for CDC.
        #define USB_DEVICE_NB_INTERFACE (X+2)
        // Total number of endpoints on this USB device.
        // This must include each endpoint for each interface.
        // Add 3 for CDC.
        #define USB_DEVICE_MAX_EP (X+3) 

2. Ensure that conf_usb.h contains the description of composite device:

   • // The endpoint numbers chosen by you for the CDC.
        // The endpoint numbers starting from 1.
        #define  UDI_CDC_DATA_EP_IN_0            (1 | USB_EP_DIR_IN)  // TX
        #define  UDI_CDC_DATA_EP_OUT_0           (2 | USB_EP_DIR_OUT) // RX
        #define  UDI_CDC_COMM_EP_0               (3 | USB_EP_DIR_IN)  // Notify endpoint
        // The interface index of an interface starting from 0
        #define  UDI_CDC_COMM_IFACE_NUMBER_0     X+0
        #define  UDI_CDC_DATA_IFACE_NUMBER_0     X+1 

3. Ensure that conf_usb.h contains the following parameters required for a USB composite device configuration:

   • // USB Interfaces descriptor structure
        #define UDI_COMPOSITE_DESC_T \
           ...
           usb_iad_desc_t udi_cdc_iad; \
           udi_cdc_comm_desc_t udi_cdc_comm; \
           udi_cdc_data_desc_t udi_cdc_data; \
           ...
        // USB Interfaces descriptor value for Full Speed
        #define UDI_COMPOSITE_DESC_FS \
           ...
           .udi_cdc_iad               = UDI_CDC_IAD_DESC_0, \
           .udi_cdc_comm              = UDI_CDC_COMM_DESC_0, \
           .udi_cdc_data              = UDI_CDC_DATA_DESC_0_FS, \
           ...
        // USB Interfaces descriptor value for High Speed
        #define UDI_COMPOSITE_DESC_HS \
           ...
           .udi_cdc_iad               = UDI_CDC_IAD_DESC_0, \
           .udi_cdc_comm              = UDI_CDC_COMM_DESC_0, \
           .udi_cdc_data              = UDI_CDC_DATA_DESC_0_HS, \
           ...
        // USB Interface APIs
        #define UDI_COMPOSITE_API \
           ...
           &udi_api_cdc_comm,       \
           &udi_api_cdc_data,       \
           ... 

   • Note

     The descriptors order given in the four lists above must be the same as the order defined by all interface indexes. The interface index orders are defined through UDI_X_IFACE_NUMBER defines.
     Also, the CDC requires a USB Interface Association Descriptor (IAD) for composite device.