Control Commands for USB Devices
Last modified by Microchip on 2023/11/09 08:55
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 request 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 or 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 endpoint. |
| 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)