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82801AA and 82801AB Datasheet
10-11
USB Controller Registers (D31:F2)
This HCHalted bit can also be used outside of Software Debug mode to indicate when the Host
Controller has detected the Run/Stop bit and has completed the current transaction. Outside of the
Software Debug mode, setting the Run/Stop bit to 0 always resets the SOF counter so that when the
Run/Stop bit is set the Host Controller starts over again from the frame list location pointed to by
the Frame List Index (see FRNUM Register description) rather than continuing where it stopped.
10.2.2
USBSTA—USB Status Register
I/O Offset:
Default Value:
Base + (02–03h)
0000h
Attribute:
Size:
Read/ Write Clear
16 bits
This register indicates pending interrupts and various states of the Host Controller. The status
resulting from a transaction on the serial bus is not indicated in this register. Software sets a bit to 0
in this register by writing a 1 to it.
Bit
Description
15:6
Reserved.
5
HCHalted.
The Host Controller sets this bit to 1 after it has stopped executing as a result of the
Run/Stop bit being set to 0, either by software or by the Host Controller hardware (debug mode or
an internal error).
4
Host Controller Process Error.
The Host Controller sets this bit to 1 when it detects a fatal error
and indicates that the Host Controller suffered a consistency check failure while processing a
Transfer Descriptor. An example of a consistency check failure would be finding an illegal PID field
while processing the packet header portion of the TD. When this error occurs, the Host Controller
clears the Run/Stop bit in the Command register to prevent further schedule execution. A hardware
interrupt is generated to the system.
3
Host System Error.
The Host Controller sets this bit to 1 when a serious error occurs during a host
system access involving the Host Controller module. In a PCI system, conditions that set this bit to
1 include PCI Parity error, PCI Master Abort, and PCI Target Abort. When this error occurs, the
Host Controller clears the Run/Stop bit in the Command register to prevent further execution of the
scheduled TDs. A hardware interrupt is generated to the system.
2
Resume Detect (RSM_DET).
The Host Controller sets this bit to 1 when it receives a “RESUME”
signal from a USB device. This is only valid if the Host Controller is in a global suspend state (bit 3
of Command register = 1).
1
USB Error Interrupt.
The Host Controller sets this bit to 1 when completion of a USB transaction
results in an error condition (e.g., error counter underflow). If the TD on which the error interrupt
occurred also had its IOC bit set, both this bit and Bit 0 are set.
0
USB Interrupt (USBINT).
The Host Controller sets this bit to 1 when the cause of an interrupt is a
completion of a USB transaction whose Transfer Descriptor had its IOC bit set. The Host Controller
also sets this bit to 1 when a short packet is detected (actual length field in TD is less than
maximum length field in TD), and short packet detection is enabled in that TD.