USB/IP protocol¶
PRELIMINARY DRAFT, MAY CONTAIN MISTAKES! 28 Jun 2011
The USB/IP protocol follows a server/client architecture. The server exports the USB devices and the clients imports them. The device driver for the exported USB device runs on the client machine.
The client may ask for the list of the exported USB devices. To get the list the client opens a TCP/IP connection towards the server, and sends an OP_REQ_DEVLIST packet on top of the TCP/IP connection (so the actual OP_REQ_DEVLIST may be sent in one or more pieces at the low level transport layer). The server sends back the OP_REP_DEVLIST packet which lists the exported USB devices. Finally the TCP/IP connection is closed.
virtual host controller usb host
"client" "server"
(imports USB devices) (exports USB devices)
| |
| OP_REQ_DEVLIST |
| ----------------------------------------------> |
| |
| OP_REP_DEVLIST |
| <---------------------------------------------- |
| |
Once the client knows the list of exported USB devices it may decide to use one of them. First the client opens a TCP/IP connection towards the server and sends an OP_REQ_IMPORT packet. The server replies with OP_REP_IMPORT. If the import was successful the TCP/IP connection remains open and will be used to transfer the URB traffic between the client and the server. The client may send two types of packets: the USBIP_CMD_SUBMIT to submit an URB, and USBIP_CMD_UNLINK to unlink a previously submitted URB. The answers of the server may be USBIP_RET_SUBMIT and USBIP_RET_UNLINK respectively.
virtual host controller usb host
"client" "server"
(imports USB devices) (exports USB devices)
| |
| OP_REQ_IMPORT |
| ----------------------------------------------> |
| |
| OP_REP_IMPORT |
| <---------------------------------------------- |
| |
| |
| USBIP_CMD_SUBMIT(seqnum = n) |
| ----------------------------------------------> |
| |
| USBIP_RET_SUBMIT(seqnum = n) |
| <---------------------------------------------- |
| . |
| : |
| |
| USBIP_CMD_SUBMIT(seqnum = m) |
| ----------------------------------------------> |
| |
| USBIP_CMD_SUBMIT(seqnum = m+1) |
| ----------------------------------------------> |
| |
| USBIP_CMD_SUBMIT(seqnum = m+2) |
| ----------------------------------------------> |
| |
| USBIP_RET_SUBMIT(seqnum = m) |
| <---------------------------------------------- |
| |
| USBIP_CMD_SUBMIT(seqnum = m+3) |
| ----------------------------------------------> |
| |
| USBIP_RET_SUBMIT(seqnum = m+1) |
| <---------------------------------------------- |
| |
| USBIP_CMD_SUBMIT(seqnum = m+4) |
| ----------------------------------------------> |
| |
| USBIP_RET_SUBMIT(seqnum = m+2) |
| <---------------------------------------------- |
| . |
| : |
| |
| USBIP_CMD_UNLINK |
| ----------------------------------------------> |
| |
| USBIP_RET_UNLINK |
| <---------------------------------------------- |
| |
The fields are in network (big endian) byte order meaning that the most significant byte (MSB) is stored at the lowest address.
- OP_REQ_DEVLIST:
Retrieve the list of exported USB devices.
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
2 |
0x0100 |
Binary-coded decimal USBIP version number: v1.0.0 |
2 |
2 |
0x8005 |
Command code: Retrieve the list of exported USB devices. |
4 |
4 |
0x00000000 |
Status: unused, shall be set to 0 |
- OP_REP_DEVLIST:
Reply with the list of exported USB devices.
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
2 |
0x0100 |
Binary-coded decimal USBIP version number: v1.0.0. |
2 |
2 |
0x0005 |
Reply code: The list of exported USB devices. |
4 |
4 |
0x00000000 |
Status: 0 for OK |
8 |
4 |
n |
Number of exported devices: 0 means no exported devices. |
0x0C |
From now on the exported n devices are described, if any. If no devices are exported the message ends with the previous “number of exported devices” field. |
||
256 |
path: Path of the device on the host exporting the USB device, string closed with zero byte, e.g. “/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2” The unused bytes shall be filled with zero bytes. |
||
0x10C |
32 |
busid: Bus ID of the exported device, string closed with zero byte, e.g. “3-2”. The unused bytes shall be filled with zero bytes. |
|
0x12C |
4 |
busnum |
|
0x130 |
4 |
devnum |
|
0x134 |
4 |
speed |
|
0x138 |
2 |
idVendor |
|
0x13A |
2 |
idProduct |
|
0x13C |
2 |
bcdDevice |
|
0x13E |
1 |
bDeviceClass |
|
0x13F |
1 |
bDeviceSubClass |
|
0x140 |
1 |
bDeviceProtocol |
|
0x141 |
1 |
bConfigurationValue |
|
0x142 |
1 |
bNumConfigurations |
|
0x143 |
1 |
bNumInterfaces |
|
0x144 |
m_0 |
From now on each interface is described, all together bNumInterfaces times, with the the following 4 fields: |
|
1 |
bInterfaceClass |
||
0x145 |
1 |
bInterfaceSubClass |
|
0x146 |
1 |
bInterfaceProtocol |
|
0x147 |
1 |
padding byte for alignment, shall be set to zero |
|
0xC + i*0x138 + m_(i-1)*4 |
The second exported USB device starts at i=1 with the busid field. |
- OP_REQ_IMPORT:
Request to import (attach) a remote USB device.
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
2 |
0x0100 |
Binary-coded decimal USBIP version number: v1.0.0 |
2 |
2 |
0x8003 |
Command code: import a remote USB device. |
4 |
4 |
0x00000000 |
Status: unused, shall be set to 0 |
8 |
32 |
busid: the busid of the exported device on the remote host. The possible values are taken from the message field OP_REP_DEVLIST.busid. A string closed with zero, the unused bytes shall be filled with zeros. |
- OP_REP_IMPORT:
Reply to import (attach) a remote USB device.
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
2 |
0x0100 |
Binary-coded decimal USBIP version number: v1.0.0 |
2 |
2 |
0x0003 |
Reply code: Reply to import. |
4 |
4 |
0x00000000 |
Status:
|
8 |
From now on comes the details of the imported device, if the previous status field was OK (0), otherwise the reply ends with the status field. |
||
256 |
path: Path of the device on the host exporting the USB device, string closed with zero byte, e.g. “/sys/devices/pci0000:00/0000:00:1d.1/usb3/3-2” The unused bytes shall be filled with zero bytes. |
||
0x108 |
32 |
busid: Bus ID of the exported device, string closed with zero byte, e.g. “3-2”. The unused bytes shall be filled with zero bytes. |
|
0x128 |
4 |
busnum |
|
0x12C |
4 |
devnum |
|
0x130 |
4 |
speed |
|
0x134 |
2 |
idVendor |
|
0x136 |
2 |
idProduct |
|
0x138 |
2 |
bcdDevice |
|
0x139 |
1 |
bDeviceClass |
|
0x13A |
1 |
bDeviceSubClass |
|
0x13B |
1 |
bDeviceProtocol |
|
0x13C |
1 |
bConfigurationValue |
|
0x13D |
1 |
bNumConfigurations |
|
0x13E |
1 |
bNumInterfaces |
- USBIP_CMD_SUBMIT:
Submit an URB
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
4 |
0x00000001 |
command: Submit an URB |
4 |
4 |
seqnum: the sequence number of the URB to submit |
|
8 |
4 |
devid |
|
0xC |
4 |
direction:
|
|
0x10 |
4 |
ep: endpoint number, possible values are: 0…15 |
|
0x14 |
4 |
transfer_flags: possible values depend on the URB transfer type, see below |
|
0x18 |
4 |
transfer_buffer_length |
|
0x1C |
4 |
start_frame: specify the selected frame to transmit an ISO frame, ignored if URB_ISO_ASAP is specified at transfer_flags |
|
0x20 |
4 |
number_of_packets: number of ISO packets |
|
0x24 |
4 |
interval: maximum time for the request on the server-side host controller |
|
0x28 |
8 |
setup: data bytes for USB setup, filled with zeros if not used |
|
0x30 |
URB data. For ISO transfers the padding between each ISO packets is not transmitted. |
Allowed transfer_flags
value
control
interrupt
bulk
isochronous
URB_SHORT_NOT_OK
0x00000001
only in
only in
only in
no
URB_ISO_ASAP
0x00000002
no
no
no
yes
URB_NO_TRANSFER_DMA_MAP
0x00000004
yes
yes
yes
yes
URB_ZERO_PACKET
0x00000040
no
no
only out
no
URB_NO_INTERRUPT
0x00000080
yes
yes
yes
yes
URB_FREE_BUFFER
0x00000100
yes
yes
yes
yes
URB_DIR_MASK
0x00000200
yes
yes
yes
yes
- USBIP_RET_SUBMIT:
Reply for submitting an URB
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
4 |
0x00000003 |
command |
4 |
4 |
seqnum: URB sequence number |
|
8 |
4 |
devid |
|
0xC |
4 |
direction:
|
|
0x10 |
4 |
ep: endpoint number |
|
0x14 |
4 |
status: zero for successful URB transaction, otherwise some kind of error happened. |
|
0x18 |
4 |
n |
actual_length: number of URB data bytes |
0x1C |
4 |
start_frame: for an ISO frame the actually selected frame for transmit. |
|
0x20 |
4 |
number_of_packets |
|
0x24 |
4 |
error_count |
|
0x28 |
8 |
setup: data bytes for USB setup, filled with zeros if not used |
|
0x30 |
n |
URB data bytes. For ISO transfers the padding between each ISO packets is not transmitted. |
- USBIP_CMD_UNLINK:
Unlink an URB
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
4 |
0x00000002 |
command: URB unlink command |
4 |
4 |
seqnum: URB sequence number to unlink:
|
|
8 |
4 |
devid |
|
0xC |
4 |
direction:
|
|
0x10 |
4 |
ep: endpoint number: zero |
|
0x14 |
4 |
seqnum: the URB sequence number given previously at USBIP_CMD_SUBMIT.seqnum field |
|
0x30 |
n |
URB data bytes. For ISO transfers the padding between each ISO packets is not transmitted. |
- USBIP_RET_UNLINK:
Reply for URB unlink
Offset |
Length |
Value |
Description |
|---|---|---|---|
0 |
4 |
0x00000004 |
command: reply for the URB unlink command |
4 |
4 |
seqnum: the unlinked URB sequence number |
|
8 |
4 |
devid |
|
0xC |
4 |
direction:
|
|
0x10 |
4 |
ep: endpoint number |
|
0x14 |
4 |
status: This is the value contained in the urb->status in the URB completition handler.
|
|
0x30 |
n |
URB data bytes. For ISO transfers the padding between each ISO packets is not transmitted. |