307013-003 Datasheet, PDF (202/848 Pages) Intel Corporation – Intel I/O Controller Hub 7

Functional Description
5.19.6.1
Transaction-Based Interrupts
These interrupts are not signaled until after the status for the last complete transaction
in the frame has been written back to host memory. This ensures that software can
safely process through (Frame List Current Index -1) when it is servicing an interrupt.
CRC Error / Time-Out
A CRC/Time-Out error occurs when a packet transmitted from the ICH7 to a USB device
or a packet transmitted from a USB device to the ICH7 generates a CRC error. The ICH7
is informed of this event by a time-out from the USB device or by the ICH7’s CRC
checker generating an error on reception of the packet. Additionally, a USB bus time-
out occurs when USB devices do not respond to a transaction phase within 19-bit times
of an EOP. Either of these conditions causes the C_ERR field of the TD to decrement.
When the C_ERR field decrements to 0, the following occurs:
• The Active bit in the TD is cleared
• The Stalled bit in the TD is set
• The CRC/Time-out bit in the TD is set.
• At the end of the frame, the USB Error Interrupt bit is set in the HC status register.
If the CRC/Time out interrupt is enabled in the Interrupt Enable register, a hardware
interrupt will be signaled to the system.
Interrupt on Completion
Transfer Descriptors contain a bit that can be set to cause an interrupt on their
completion. The completion of the transaction associated with that block causes the
USB Interrupt bit in the HC Status Register to be set at the end of the frame in which
the transfer completed. When a TD is encountered with the IOC bit set to 1, the IOC bit
in the HC Status register is set to 1 at the end of the frame if the active bit in the TD is
set to 0 (even if it was set to 0 when initially read).
If the IOC Enable bit of Interrupt Enable register (bit 2 of I/O offset 04h) is set, a
hardware interrupt is signaled to the system. The USB Interrupt bit in the HC status
register is set either when the TD completes successfully or because of errors. If the
completion is because of errors, the USB Error bit in the HC status register is also set.
Short Packet Detect
A transfer set is a collection of data which requires more than one USB transaction to
completely move the data across the USB. An example might be a large print file which
requires numerous TDs in multiple frames to completely transfer the data. Reception of
a data packet that is less than the endpoint’s Max Packet size during Control, Bulk or
Interrupt transfers signals the completion of the transfer set, even if there are active
TDs remaining for this transfer set. Setting the SPD bit in a TD indicates to the HC to
set the USB Interrupt bit in the HC status register at the end of the frame in which this
event occurs. This feature streamlines the processing of input on these transfer types.
If the Short Packet Interrupt Enable bit in the Interrupt Enable register is set, a
hardware interrupt is signaled to the system at the end of the frame where the event
occurred.
202
Intel ^® ICH7 Family Datasheet