Atmel Software Framework

MSC 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 MSC (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+1)
#define USB_DEVICE_MAX_EP (X+2)
#define UDI_MSC_EP_IN (X | USB_EP_DIR_IN)
#define UDI_MSC_EP_OUT (Y | USB_EP_DIR_OUT)
#define UDI_MSC_IFACE_NUMBER X
#define UDI_COMPOSITE_DESC_T \
udi_msc_desc_t udi_msc; \
...
#define UDI_COMPOSITE_DESC_FS \
.udi_msc = UDI_MSC_DESC, \
...
#define UDI_COMPOSITE_DESC_HS \
.udi_msc = UDI_MSC_DESC, \
...
#define UDI_COMPOSITE_API \
&udi_api_msc, \
...

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 1 for MSC.
      #define USB_DEVICE_NB_INTERFACE (X+1)
      // Total number of endpoints on this USB device.
      // This must include each endpoint for each interface.
      // Add 2 for MSC.
      #define USB_DEVICE_MAX_EP (X+2)
  2. Ensure that conf_usb.h contains the description of composite device:
    • // The endpoint numbers chosen by you for the MSC.
      // The endpoint numbers starting from 1.
      #define UDI_MSC_EP_IN (X | USB_EP_DIR_IN)
      #define UDI_MSC_EP_OUT (Y | USB_EP_DIR_OUT)
      // The interface index of an interface starting from 0
      #define UDI_MSC_IFACE_NUMBER X
  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 \
      ...
      udi_msc_desc_t udi_msc; \
      ...
      // USB Interfaces descriptor value for Full Speed
      #define UDI_COMPOSITE_DESC_FS \
      ...
      .udi_msc = UDI_MSC_DESC_FS, \
      ...
      // USB Interfaces descriptor value for High Speed
      #define UDI_COMPOSITE_DESC_HS \
      ...
      .udi_msc = UDI_MSC_DESC_HS, \
      ...
      // USB Interface APIs
      #define UDI_COMPOSITE_API \
      ...
      ...
    • 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.