Universal Serial Bus (USB)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
31-29
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
Table 31-17
. Errors which exclusively exist in
either host mode or function mode are marked as such.
Table 31-18
describes the USB controller reception errors.
Table 31-17. USB Controller Transmission Errors
Error
Description
Transmit
Underrun
If an underrun occurs, the transmitter forces a bit stuffing violation, terminates buffer transmission, closes
the buffer, sets TxBD[UN] and the corresponding USBER[TXE
n]. The endpoint resumes transmission
after the
RESTART
TX
ENDPOINT
command is received.
Transmit
Timeout
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
TxBD[TO] and USBER[TXE
n]. The endpoint resumes transmission after receiving a
RESTART
TX
ENDPOINT
command.
Tx Data Not
Ready
For
USB function mode
only.
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
nak or stall
hand shake
For
USB host mode
only.
If this error occurs, the channel closes the buffer, sets the corresponding status bit in the TxBD (nak or
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. USB Controller Reception Errors
Error Description
Overrun
Error
If the 16-byte receive FIFO overruns, the previously received byte is overwritten. The controller closes the
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
Octet-Alig
ned
Packet
If this error occurs, the controller writes the received data to the buffer, closes the buffer and sets both
RxBD[NO] and USBER[RXB].
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.
Summary of Contents for PowerQUICC MPC870
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