Freescale Semiconductor MCF54455 Reference Manual page 275

Universal Serial Bus Interface – On-The-Go Module
For TX-ISO, MULT counter can be loaded with a lesser value in the dTD
multiplier override field. If the multiplier override field is zero, the MULT
counter initializes to the multiplier in the QH.
• RX packet retired:
— MULT counter reaches zero.
— Non-MDATA data PID is received
— Overflow error:
– Packet received is > maximum packet length. (Buffer Error bit is set)
– Packet received exceeds total bytes allocated in dTD. (Buffer Error bit is set)
— Fulfillment error (Transaction Error bit is set):
– # packets occurred > 0 AND # packets occurred < MULT
— CRC error (Transaction Error bit is set)
For ISO, when a dTD is retired, the next dTD is primed for the next frame.
For continuous (micro)frame to (micro)frame operation, DCD must ensure
the dTD linked-list is out ahead of the device controller by at least two
(micro)frames.
Isochronous Pipe Synchronization
When it is necessary to synchronize an isochronous data pipe to the host, the (micro)frame number
(FRINDEX register) can act as a marker. To cause a packet transfer to occur at a specific (micro)frame
number (N), the DCD must interrupt on SOF during frame N-1. When the FRINDEX equals N-1, the DCD
must write the prime bit. The USB OTG primes the isochronous endpoint in (micro)frame N-1 so the
device controller executes delivery during (micro)frame N.
Priming an endpoint towards the end of (micro)frame N-1 does not
guarantee delivery in (micro)frame N. The delivery may actually occur in
(micro)frame N+1 if the device controller does not have enough time to
complete the prime before the SOF for packet N is received.
Isochronous Endpoint Bus Response Matrix
Token
Type
Setup
10-68
CAUTION
Table 10-57. Isochronous Endpoint Bus Response Matrix
Not
Stall
Primed
STALL STALL
1
NULL NULL
In
Packet Packet
NOTE
NOTE
Primed Underflow
STALL N/A
2
Transmit BS Error
Overflow
N/A
N/A
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