Universal Host Controller Interface

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Universal Host Controller Interface (UHCI) was created by Intel as an implementation of the USB 1.0 host controller interface. Along with OHCI, it makes up the USB 1.0 standard.


Technical Details

The UHCI specification defines a set of I/O mapped registers that allow communication between the controller and the operating system. The base address for these registers can be found by searching the PCI controller for a specific VendorID/DeviceID combination, or for a specific ClassID/SubclassID/Interface combination. All UHCI PCI controllers will have a Class ID of 0x0C, a Subclass ID of 0x03, and an Interface value of 0x00. The PCI Configuration space for this device will contain the I/O port address information in BAR4. This may be different from other standards such as OHCI or EHCI.

I/O Registers

Offset (Hex) Name Description
00 USBCMD Usb Command
02 USBSTS Usb Status
04 USBINTR Usb Interrupt Enable
06 FRNUM Frame Number
08 FRBASEADD Frame List Base Address
0C SOFMOD Start Of Frame Modify
10 PORTSC1 Port 1 Status/Control
12 PORTSC2 Port 2 Status/Control

Command Register

Bits Name Description
15-8 Reserved
7 Max Packet
6 Configure
5 Software Debug
4 Global Resume
3 Global Suspend
2 Global Reset
1 Host Controller Reset
0 Run

Status Register

Bits Name Description
15-6 Reserved
5 Halted
4 Process Error
3 System Error
2 Resume Detected
1 Error Interrupt
0 Interrupt

Interrupt Enable Register

Bits Name Description
15-4 Reserved
3 Short Packet
2 Complete
1 Resume
0 Timeout CRC

Port 1/2 Status/Control Registers

Bits Name Description
15-13 Reserved
12 Suspend
11-10 Reserved
9 Reset
8 Low Speed
7 Reserved (Must be 1)
6 Resume Detected
5-4 Line Status
3 Port Enable Changed
2 Port Enabled
1 Connected Changed
0 Connected

Frame List Entry

Bits Name Description
31-4 First Descriptor Address
3 Reserved
2 Process Full Queue
1 0 = next entry is TD 1 = next entry is QH
0 Is Empty

UHCI Descriptor

Offset (Hex) Name Description Lenght
00 Next Descriptor Same as Frame Entry Above 4 byte lenght
04 Status See below 4 byte lenght
08 Packet Header See below 4 byte lenght
12 Buffer Address 32-bit address of data buffer 4 byte lenght
16 System Use 128-bit area reserved for use by the system 16 byte lenght

UHCI Descriptor Status

Bits Name Description
31-30 Reserved
29 Short Packet Detect
28-27 Error Counter
26 Low Speed
25 Is Isochronous
24 Interrupt On Complete
23 Active Set by UHCI Controller
22 Stalled Set by UHCI Controller
21 Data Buffer Error Set by UHCI Controller
20 Babble Detected Set by UHCI Controller
19 Non-Acknowledged Set by UHCI Controller
18 Timeout CRC Set by UHCI Controller
17 Bit Stuff Error Set by UHCI Controller
16-11 Reserved
10-0 Actual Length

UHCI Descriptor Packet Header

Bits Name Description
31-21 Maximum Length (Length - 1) so 7 for low speed, 63 for full speed
20 Reserved
19 Data Toggle
18-15 Endpoint
14-8 Device
7-0 Packet Type 0x69 = IN, 0xE1 = OUT, 0x2D = SETUP, other values are invalid

See Also

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