Control Commands for USB Devices

USB provides the Host the ability to send control commands to standard Devices as well as Hubs. Devices receive the control commands on endpoint 0.

Setup Packet

Each control request starts with an 8 byte Setup Packet.
Field Size
(bytes)
Description
bmRequestType 1 Specifies the type of request and the recipient. (See the following table for the details of bmRequest)
bRequest 1 The command to be executed. The values of bRequest are listed in the descriptions of the requests types
wValue 2 command parameter, if needed
wIndex 2 command parameter, if needed
wLength 2 Number of additional bytes to transfer if the instruction has a data phase

bmRequest type

Bit Field Purpose Value
D0 - D4 Recipient 0 - Device
1 - Endpoint
2 - Interface
3 - Other
4-31 Reserved
D5 - D6 Type of Request 0 - Standard
1 - Class
2 - Vendor
3 - Reserved
D7 Direction 0 - Host to Device
1 - Device to Host

Many commands require no additional data, and are completed by the device within 50 ms of sending the Setup Packet. Requests which require a data phase must be completed by the Device within 500 ms of the packet being sent.

There are four types of control commands:

  • Device Requests
  • Interface Requests
  • Endpoint Requests
  • Hub Requests

Device Requests

bmRequestType bRequest Description
1000 0000b GET_STATUS
( 0 )
Returns the Status of the Device. Primarily used to determine if the Device is capable of Remote Wake-up , and whether of not the Device is Self or Bus-powered
0000 0000b CLEAR_FEATURE
(01)
Disables either the DEVICE_REMOTE_WAKEUP , or the TEST_MODE feature.
0000 0000b SET_FEATURE
(03)
Enables either the DEVICE_REMOTE_WAKEUP , or the TEST_MODE feature.
0000 0000b SET_ADDRESS
(05)
During enumeration this instruction is used to assign an address (1 -127) to the Device.
1000 0000b GET_DESCRIPTOR
(06)
Returns the descriptor table selected by the wValue parameter.
0000 0000b SET_DESCRIPTOR
(07)
Sets the specified descriptor value.
1000 0000b GET_CONFIGURATION
(08)
Returns the index value for the active Device configuration
0000 0000b SET_CONFIGURATION
(09)
Cause the specified Device configuration to become active.

Interface Requests

bmRequestType bRequest Description
1000 0001b GET_STATUS
(0)
Returns the status of the interface, Currently both returned bytes are "reserved for future use".
0000 0001b CLEAR_FEATURE
(01)
Disables an interface feature
0000 0001b SET_FEATURE
(03)
Enables the specified interface feature
1000 0001b GET_INTERFACE
(0A)
Retrieve the index for the currently active Interface
0000 0001b SET_INTERFACE
(11)
Indicated with Interface to activate

Endpoint Requests

bmRequestType bRequest Description
1000 0010b GET_STATUS
(0)
Returns the status of the end point
0000 0010b CLEAR_FEATURE
(01)
Disables an endpoint feature
0000 0010b SET_FEATURE
(03)
Enable endpoint feature
1000 0010b SYNCH_FRAME
(12)
Used to report endpoint synchronization frame

Hub Requests

Get Hub Status (GET_STATUS)
Get Port Status (GET_STATUS)
Clear Hub Feature (CLEAR_FEATURE)
Clear Port Feature (CLEAR_FEATURE)
Get Bus State (GET_STATE) obsolete since USB 2.0
Set Hub Feature (SET_FEATURE)
Set Port Feature (SET_FEATURE)
Get Hub Descriptor (GET_DESCRIPTOR)
Set Hub Descriptor (SET_DESCRIPTOR)
Clear TT Buffer (CLEAR_TT_BUFFER)
Reset TT (RESET_TT)
Get TT State (GET_TT_STATE)
Stop TT (STOP_TT)

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