AVR293: USB Composite Device
8-bit
Microcontrollers
Features
• Combining several USB applications using ONE DEVICE
• No HUB needed
• Bus powered
Application Note
1. Introduction
Adding to the flexibility given to the user with the Hot Plug & Play, supplying power
from the bus, the automatic detection of the insertion and remove of the device and by
providing different transfer modes, the USB allows the user to manage several USB
applications using ONE device called “COMPOSITE DEVICE”.
The aim of this document is to describe how to start and implement a composite
device application.
A familiarity with USB Software Library for AT90USBxxx Microcontrollers (Doc 7675,
Included in the CD-ROM & Atmel website) and the CDC specification
(http://www.usb.org) is assumed.
Figure 1-1.
Composite Device Application
1 M CU
USB interface
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2. Hardware Requirements
The USB CDC application requires the following hardware:
1. AVR USB evaluation board (STK525, AT90USBKey, STK526, EVK527...or your own
board)
2. AVR USB microcontroller
3. USB cable (Standard A to Mini B)
4. PC running on Windows® (2000, XP) with USB 1.1 or 2.0 host
Note:
Another STK 52x and USB port are required if the PC has no RS232 interface.
3. In system programming and Device Firmware Upgrade
To program the device you can use the following methods:
• The JTAG interface using the JTAGICE MKII
• The SPI interface using the AVRISP MKII
• The USB interface thanks to the factory DFU bootloader and Flip software
• The parallel programming using the STK500 or the STK600
Please refer to the hardware user guide of the board you are using (if you are using Atmel starter
kit) to see how to program the device using one of these different methods.
Please refer to Flip(1) help content to see how to install the USB driver and program the device
through the USB interface.
(1)Flip is a software provided by atmel to allow the user to program the AVR USB devices
through the USB interface (No external hardware required) thanks to the factory DFU
bootloader.
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4. Quick Start
Once your device is programmed with hex file (depending on which composite device demo you
are using), click on Start Application button on Flip or push the reset button from the used board
to start the composite device demonstration. Check that your device is enumerated as composite device (see Figure 6-1), then you can use the board as a mouse, removable disk and Generic
HID (you may have less or more applications depending on which demo you are using) at the
same time.
Figure 4-1.
Composite Device enumeration
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The figure below shows the STK525 used by the demo (you may use another kit: AT90USBKey,
STK526.., depending on the AVR USB product you are working with):
Figure 4-2.
STK525
R S 2 3 2 C o n n e c to r
U S B C o n n e c to r
J o y s t ic k
4.1
Composite Device
The purpose of the Composite Device demonstration is to show the user how to manage several
USB applications using only one USB controller.
Depending on which demonstartion you are uisng, when you cannect your device to you PC,
you will see two or more of below applications appear in your device manager, and you can use
each application in stand alone mode:
– USB mouse: you can move the mouse pointer using the joystic or the buttons of
youyr board
– USB Mass Storage (removable disk): a new removable disk will appear, and you can
transfer file with the onboard dataflash of your board (or any other memory
depending on which board you are using)
– Generic HID device: please refer to the Generic HID application note: doc7599
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5. Application Overview
To implement a Composite Device application, the user has to integrate several interfaces in his
device (one for each application).
The figure below shows the descriptors structure:
Figure 5-1.
Composite Device Overview
Device
descriptor
Configuration
Descriptor
Inetrface 1
Descriptor
Interface 2
Descriptor
...
Interface 'n'
Descriptor
To add new interface to manage an adding application using the same controller, you have to
modify the number of interfaces supported by the configuration descriptor, add the interface
descriptor, the endpoint descriptors and the related specific requests management.
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6. Firmware
As explained in the USB Software Library for AT90USBxxx Microcontrollers (Doc 7675, included
in the USB CD-ROM ) all USB firmware packages are based on the same architecture (please
refer to this document for more details).
To add new interface, the follwoing files have to be modified:
6.1
usb_descriptors.h
This file contains the definition of the descriptors’ parameters. You have to modify and add the
following parameters when you want to customize one of our demo to build a composite device
or add a new interface to a current composite device:
• Modify the VID/PID of the device descriptor. Each USB application must have its own and
unique VID/PID:
// USB Device descriptor
#define USB_SPECIFICATION
0x0200
#define DEVICE_CLASS
0
// each configuration has its own class
#define DEVICE_SUB_CLASS
class
0
// each configuration has its own sub-
#define DEVICE_PROTOCOL
protocol
0
// each configuration has its own
#define EP_CONTROL_LENGTH
64
#define VENDOR_ID
VID_ATMEL
#define PRODUCT_ID
PID_MegaMS
#define RELEASE_NUMBER
0x1000
#define MAN_INDEX
0x01
#define PROD_INDEX
0x02
#define SN_INDEX
0x03
#define NB_CONFIGURATION
1
Note:
The class, subclass and protocol parameter must be set to 0 in the device descriptor. Each interface will specify its own class/subclass/protocol parameter.
• Modify the number of interfaces supported by the configuration’s descriptor:
//
USB Configuration descriptor
#define NB_INTERFACE
N // Number of interfaces
#define CONF_NB
1
#define CONF_INDEX
0
#define CONF_ATTRIBUTES
USB_CONFIG_BUSPOWERED
#define MAX_POWER
50
// 100 mA
• Add the descriptor of your new interafce. Please note that the first interface start with the
number 0, the next one should be number 1 and so on. So, depending on how many
interfaces you have in you application, this new one should be number (n+1). “n” is the
number of the last interface.The example hereunder shows the interface’s descriptor of a
Mass Storage application:
// USB Interface descriptor
6
#define INTERFACE_NB
n+1 // Interface's number
#define ALTERNATE
0
#define NB_ENDPOINT
2
#define INTERFACE_CLASS
MS_CLASS
// Mass Storage Class
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#define INTERFACE_SUB_CLASS MS_SUB_CLASS6 // SCSI transparent Command Set
#define INTERFACE_PROTOCOL
MS_PROTOCOL
#define INTERFACE_INDEX
0
// Bulk-Only Transport
• Than, depending on the class you added with this new interface, you have to add the related
endpoint descriptors with the correct transfer mode, maximum packet lenght... and you may
need to declare specific descriptors (for example, the HID class requires a HID descriptor
and a report descriptor adding to the endpoint descriptors)
• Once all descriptors are specified and the related parameters are defined, you have to add to
the structure below:
typedef struct
{
S_usb_configuration_descriptor cfg;
S_usb_interface_descriptor
ifc0;
S_usb_endpoint_descriptor
ep1;
S_usb_endpoint_descriptor
ep2;
S_usb_interface_descriptor
ifc1;
S_usb_endpoint_descriptor
ep3;
S_usb_endpoint_descriptor
ep4;
} S_usb_user_configuration_descriptor;
Now, you have to complete the usb_descriptors.c file with the new descriptors values. Please,
see hereunder:
6.2
usb_descriptors.c
In this file, you have to add the new descriptors values in the correct order, as specified by the
USB.
6.3
usb_specific_request.c
As Mentioned above, a new interface may require a specific requests management. These
requests have to be manage by the usb_specific_request.c and specially the function
usb_user_read_request(). A new functions may be added to this file to handle a specific tasks
related to these specific requests.
This new interface has one or more endpoints. These endpoints has to be configured using the
function usb_configure_endpoint() used by the function usb_user_endpoint_init().
These modifications will allow the device to enumerate as a composite device with the new
class/subclass/protocol defined by the new interface. To use this interface you have now to add
the application layer by creating an xxx_task.c to manage your application.
7. PC Software
Depending on which interfaces you are using, you may or not need to develop a PC application.
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8. Limitations
• The number of interfaces is limited by the number and the size of the endpoints. Each
interface requires its own physical endpoints, so the user has to check that the device has
enough endpoints and DPRAM to handle the endpoints of all interfaces.
• Some Operating Systems does not support the composite device by default.
9. Related Documentation
• AVR USB Datasheet
• USB Software Library for AT90USBxxx Microcontrollers
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