
82801AA and 82801AB Datasheet
5-93
Functional Description
Bit Stuff Error
A bit stuff error results from the detection of a sequence of more that 6 ones in a row within the
incoming data stream. This causes the C_ERR field of the TD to be decremented. When the
C_ERR field decrements to zero, the Active bit in the TD is cleared to 0, the Stalled bit is set to 1,
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.
5.15.6.2
Non-Transaction Based Interrupts
If an ICH process error or system error occur, the ICH halts and immediately issues a hardware
interrupt to the system.
Resume Received
This event indicates that the ICH received a RESUME signal from a device on the USB bus during
a global suspend. If this interrupt is enabled in the Interrupt Enable register, a hardware interrupt is
signaled to the system allowing the USB to be brought out of the suspend state and returned to
normal operation.
ICH Process Error
The HC monitors certain critical fields during operation to ensure that it does not process corrupted
data structures. These include checking for a valid PID and verifying that the MaxLength field is
less than 1280. If it detects a condition that would indicate that it is processing corrupted data
structures, it immediately halts processing, sets the HC Process Error bit in the HC Status register,
and signals a hardware interrupt to the system.
This interrupt cannot be disabled through the Interrupt Enable register.
Host System Error
The ICH sets this bit to 1 when a PCI Parity error, PCI Master Abort, or PCI Target Abort occur.
When this error occurs, the ICH clears the Run/Stop bit in the Command register to prevent further
execution of the scheduled TDs. This interrupt cannot be disabled through the Interrupt Enable
register.