Freescale Semiconductor MCF52277 Reference Manual page 420

Universal Serial Bus Interface – On-The-Go Module
TX-dTD is complete when:
• All packets described in the dTD successfully transmit. Total bytes in dTD equal 0 when this
occurs.
RX-dTD is complete when:
• All packets described in the dTD are successfully received. Total bytes in dTD equal 0 when this
occurs.
• A short packet (number of bytes < maximum packet length) was received.
This is a successful transfer completion; DCD must check the total bytes field in the dTD to
determine the number of bytes remaining. From the total bytes remaining in the dTD, the DCD can
compute the actual bytes received.
• A long packet was received (number of bytes > maximum packet size) or (total bytes received >
total bytes specified).
This is an error condition. The device controller discards the remaining packet and set the buffer
error bit in the dTD. In addition, the endpoint flushes and the USBERR interrupt becomes active.
Disabling zero-length packet termination allows transfers larger than the
total bytes field spanning across two or more dTDs.
Upon successful completion of the packet(s) described by the dTD, the active bit in the dTD is cleared and
the next pointer is followed when the terminate bit is clear. When the terminate bit is set, USB OTG flushes
the endpoint/direction and ceases operations for that endpoint/direction.
Upon unsuccessful completion of a packet (see long packet above), the dQH is left pointing to the dTD in
error. To recover from this error condition, DCD must properly re-initialize the dQH by clearing the active
bit and update the nextTD pointer before attempting to re-prime the endpoint.
All packet level errors, such as a missing handshake or CRC error, are
retried automatically by the device controller. There is no required
interaction with the DCD for managing such errors.
Token
Type
Setup
In
Out
Ping
Invalid
1
Force bit stuff error
20-62
Table 20-54. Interrupt/Bulk Endpoint Bus Response Matrix
Not
Stall
Primed
Ignore Ignore
STALL NAK
STALL NAK
STALL NAK
Ignore Ignore
MCF52277 Reference Manual, Rev. 1
NOTE
NOTE
Primed Underflow
Ignore
Transmit BS Error
2
Receive + NYET/ACK
ACK
Ignore
Overflow
N/A N/A
1
N/A
N/A NAK
N/A N/A
Ignore Ignore
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