Computer Hardware User Manual

Universal Serial Bus (USB) Configuration
13-12 Intel® 460GX Chipset Software Developer’s Manual
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.
13.3.7 PORTSC–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
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
Bit Description
15:13 Reserved. Must written as 0s when writing this register.