Functional Description
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.
Serial Bus Babble
When a device transmits on the USB for a time greater than its assigned Max Length, it
is said to be babbling. Since isochrony can be destroyed by a babbling device, this error
results in the Active bit in the TD being cleared to 0 and the Stalled and Babble bits
being set to 1. The C_ERR field is not decremented for a babble. The USB Error
Interrupt bit in the HC Status register is set to 1 at the end of the frame. A hardware
interrupt is signaled to the system.
If an EOF babble was caused by the ICH10 (due to incorrect schedule for instance), the
ICH10 forces a bit stuff error followed by an EOP and the start of the next frame.
Stalled
This event indicates that a device/endpoint returned a STALL handshake during a
transaction or that the transaction ended in an error condition. The TDs Stalled bit is
set and the Active bit is cleared. Reception of a STALL does not decrement the error
counter. A hardware interrupt is signaled to the system.
Data Buffer Error
This event indicates that an overrun of incoming data or a under-run of outgoing data
has occurred for this transaction. This would generally be caused by the ICH10 not
being able to access required data buffers in memory within necessary latency
requirements. Either of these conditions causes the C_ERR field of the TD to be
decremented.
When C_ERR decrements to 0, the Active bit in the TD is cleared, the Stalled bit is set,
the USB Error Interrupt bit in the HC Status register is set to 1 at the end of the frame
and a hardware interrupt is signaled to the system.
Datasheet
195
INTEL [ INTEL ]
