Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 877

31.14 USB Controller Errors
The USB controller reports frame reception and transmission error conditions using the BDs and the USB
event register (USBER). Transmission errors are shown in
either host mode or function mode are marked as such.
Error
Transmit If an underrun occurs, the transmitter forces a bit stuffing violation, terminates buffer transmission, closes
Underrun the buffer, sets TxBD[UN] and the corresponding USBER[TXE n ]. The endpoint resumes transmission
after the
RESTART TX ENDPOINT
Transmit Transmit packet not acknowledged. If a timeout occurs, the controller tries to retransmit if
USEP n [RTE] = 1. If RTE = 0 or the second attempt fails, the controller closes the buffer and sets
Timeout
TxBD[TO] and USBER[TXE n ]. The endpoint resumes transmission after receiving a
command.
ENDPOINT
Tx Data Not For USB function mode only.
Ready This error occurs if an IN token is received, but the corresponding endpoint's transmit FIFO is empty, or
if the target endpoint is configured to NAK or STALL. The controller sets USBER[TXE n ].
reception of For USB host mode only.
nak or stall If this error occurs, the channel closes the buffer, sets the corresponding status bit in the TxBD (nak or
hand shake stal), and sets the TXE bit in the USB event register. The host will resume transmission after reception
of the RESTART TRANSMIT command.
Table 31-18 describes the USB controller reception errors.
Error
Overrun If the 16-byte receive FIFO overruns, the previously received byte is overwritten. The controller closes the
Error buffer and sets both RxBD[OV] and USBER[RXB].
For USB function mode the NAK handshake is sent after the end of the received packet if the packet was
received error-free.
Busy Error A frame was received and discarded due to lack of buffers. The controller sets USBER[BSY].
Non If this error occurs, the controller writes the received data to the buffer, closes the buffer and sets both
Octet-Alig RxBD[NO] and USBER[RXB].
ned
Packet
CRC Error When a CRC error occurs, the controller closes the buffer, and sets both RxBD[CR] and USBER[RXB].
In isochronous mode (USEP n [TM] = 0b11), the USB controller reports a CRC error; however, there are
no handshake packets (ACK) and the transfer continues normally when an error occurs.
Freescale Semiconductor
Table 31-17. USB Controller Transmission Errors
command is received.
Table 31-18. USB Controller Reception Errors
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Table 31-17. Errors which exclusively exist in
Description
Description
Universal Serial Bus (USB)
RESTART TX
31-29