Universal Serial Bus (USB) Configuration

required by the USB specification. It’s initial programmed value is system dependent based on the accuracy of hardware USB clock and is initialized by system BIOS. It may be reprogrammed by USB system software at any time. Its value will take effect from the beginning of the next frame. This register is reset upon a Host Controller Reset or Global Reset. Software must maintain a copy of its value for reprogramming if necessary.

Bit

 

Description

 

 

7

Reserved.

 

 

6:0

SOF Timing Value. Guidelines for the modification of frame time are contained in Chapter 7 of the

 

USB Specification. The SOF cycle time (number of SOF counter clock periods to generate a SOF

 

frame length) is equal to 11936 + value in this field. The default value is decimal 64 which gives a

 

SOF cycle time of 12000. For a 12 MHz SOF counter clock input, this produces a 1 ms Frame

 

period. The following table indicates what SOF Timing Value to program into this field for a certain

 

frame period.

 

Frame Length

 

(# 12 MHz Clocks) SOF Reg. Value

 

(decimal) (decimal)

 

11936

0

 

11937

1

 

. .

 

 

. .

 

 

11999

63

 

12000

64

 

12001

65

 

. .

 

 

. .

 

 

12062

126

 

12063

127

 

 

 

13.3.7PORTSC–Port Status and Control Register (I/O)

I/O Address:

Base + (10-11h)–Port 0

 

Base + (12-13h)–Port 1

Default:

0080h

Access:

Read/Write (WORD writeable only)

After a Power-up reset, Global reset, or Host Controller reset, the initial conditions of a port are: No device connected, Port disabled, and the bus line status is 00 (single-ended zero). Note: If a device is attached, the port state will transition to the attached state and system software will process this as with any status change notification. It may take up to 64 USB bit times for the port transition to occur. If the Host Controller is in global suspend mode, then, if any of bits [6,3,1] gets set, the Host Controller will signal a global resume. Refer to Chapter 11 of the USB Specification for details on hub operation.

Bit

Description

15:13 Reserved. Must written as 0s when writing this register.

13-12

Intel® 460GX Chipset Software Developer’s Manual