/dev/usb/oh0

/dev/usb/oh0 is used to interact with the Wii's external USB bus. This interface is very similar to /dev/usb/oh1 and has two parts: the "root" or host device, and individual devices on which USB requests can be submitted.

/dev/usb/oh0 (IOS57 and newer)

In recent versions of IOS (after IOS 57), the OHCI0 module appears to implement a different interface and seems to only register this new interface of /dev/usb/oh0.

Only IOS_OPEN, IOS_CLOSE and IOS_IOCTL are valid commands. The other commands immediately return IPC_EINVAL (-4).

Ioctl	Name	Input	Output	Notes
0	USBV2_IOCTL_GET_VERSION	-	0x20 bytes	Writes the version 0x20001 to the output buffer. This is very similar to the IOS58 version of /dev/usb/hid, which writes 0x50001 to the output buffer instead. It is also reminiscent of /dev/usb/ehc which does the same thing (but with an ioctlv).
1	?	?	?	?
2	?	?	?	?
3	?	0x20 bytes	?	?
4	?	0x20 bytes	?	?
5	?	0x20 bytes	?	?
16	?	0x20 bytes	?	?
17	?	0x20 bytes	?	?
18	?	0x20 bytes	?	Handled by the same function as for ioctl 20.
19	?	0x20 bytes	?	?
20	?	0x20 bytes	?	Handled by the same function as for ioctl 18.

/dev/usb/oh0

Request	Name	Input	Output	Notes
12 (ioctlv)	USBV0_IOCTL_GETDEVLIST	2	2	in 0: u8 - number of descriptors to return in 1: u8 - interface class io 0: u8 - number of devices io 1: u32* of size num_descriptors * 8 - device list
15 (ioctl)	?	?	?	Mentioned by comex in #dolphin-dev.
27 (ioctlv)	USBV0_IOCTL_DEVINSERTHOOK	2	0	Returns when a device with the requested VID/PID is plugged in, or immediately if the device is already inserted. in 0: u16 - VID in 1: u16 - PID
30 (ioctlv)	USBV0_IOCTL_DEVINSERTHOOKID (RegisterInsertionNotifyWithId)	3	1	Returns when a device with the requested VID/PID is plugged in, or immediately if the device is already inserted. It is similar to USBV0_IOCTL_DEVINSERTHOOK, but it has an additional in vector + io vector, possibly used for passing an "ID" (according the official name). Its purpose is unknown. in 0: u16 - VID in 1: u16 - PID in 2: u8 - Unknown (00); some sort of ID? io 0: u8* of size 4 - Unknown; some sort of ID?
31 (?)	? (IUSB_CancelInsertionNotify)	?	?	?

/dev/usb/oh0/%x/%x

These devices represent an individual USB device, based on its vendor ID and product ID (in hexadecimal format without leading zeroes). It is unclear how devices with the same VID/PID can be used at the same time.

Request	Name	Input	Output	Notes
0 (ioctlv)	USBV0_IOCTL_CTRLMSG	5	1	Submits a control transfer. in 0: u8 - bmRequestType in 1: u8 - bmRequest in 2: u16 - wValue (swapped) in 3: u16 - wIndex (swapped) in 4: u16 - wLength (swapped) in 5: u8 - Unknown (00) io 0: array of length wLength - Request data
1 (ioctlv)	USBV0_IOCTL_BLKMSG	2	1	Submits a bulk transfer. in 0: u8 - Endpoint in 1: u16 - Length io 0: array of length in[1] - Payload data
2 (ioctlv)	USBV0_IOCTL_INTRMSG	2	1	Submits an interrupt transfer. in 0: u8 - Endpoint in 1: u16 - Length io 0: array of length in[1] - Payload data
5 (ioctl)	USBV0_IOCTL_SUSPENDDEV	?	?	Unknown. According to libogc, this is used for suspending a device.
6 (ioctl)	USBV0_IOCTL_RESUMEDEV	?	?	Unknown. According to libogc, this is used for resuming a device.
9 (ioctlv)	USBV0_IOCTL_ISOMSG	3	2	Submits an isochronous transfer. in 0: u8 - Endpoint in 1: u16 - Length in 2: u8 - Number of isochronous packets io 0: u16* of size in[2] - Sizes of the isochronous packets io 1: array of length in[1] - Payload data
26 (ioctlv)	USBV0_IOCTL_DEVREMOVALHOOK	0	0	Returns when the device is unplugged.
29 (ioctl)	?	-	-	Unknown. Used by Wheel of Fortune on shutdown.

Known Devices

• /dev/usb/oh0/0b95/7720: ASIX AX88772 USB2.0 to Fast Ethernet Adapter (referenced in IOS eth driver)
• /dev/usb/oh0/57e/308: Nintendo Wii Speak (microphone)
• /dev/usb/oh0/46d/a03: Logitech microphone

Errors

-4 (IPC_EINVAL): might be caused by an invalid device fd

-7003: STALL (according to gc-linux)

-7004: STALL (according to gc-linux)

-7005: NAK (according to gc-linux)

-7008

-7022