mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 956

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Programmers Interface
The following figure shows a timeline of how a typical USB token is processed after the
BDT is read and OWN=1.
The USB has two sources for the DMA overrun error:
Memory Latency
Oversized Packets
956
Non-Acknowledgment (NAK) or Bus Timeout (BTO) — See
bit 4 in "Error Interrupt Status Register (ERR_STAT)" as
appropriate for the class of transaction.
5. When the microprocessor processes the TOK_DNE interrupt, it reads from the status
6. At this point, the microprocessor allocates a new BD so additional USB data can be
The memory latency on the BVCI initiator interface may be too high and cause the
receive FIFO to overflow. This is predominantly a hardware performance issue,
usually caused by transient memory access issues.
The packet received may be larger than the negotiated MaxPacket size. Typically, this
is caused by a software bug. For DMA overrun errors due to oversized data packets,
the USB specification is ambiguous. It assumes correct software drivers on both sides.
NAKing the packet can result in retransmission of the already oversized packet data.
Therefore, in response to oversized packets, the USB core continues ACKing the
packet for non-isochronous transfers.
register all the information needed to process the endpoint.
transmitted or received for that endpoint, and then processes the last BD.
Interrupt Generated
USB_RST
Errors due to Memory Latency
USB Host
Table 39-5. USB Responses to DMA Overrun Errors
SETUP TOKEN
OUT TOKEN
IN TOKEN
USB RST
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Figure 39-4. USB Token Transaction
Table continues on the next page...
Function
Preliminary
DATA
DATA
DATA
SOF
Continues acknowledging (ACKing) the packet for non-
isochronous transfers.
SOF Interrupt Generated
Errors due to Oversized Packets
ACK
ACK
ACK
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Interrupt Generated
Interrupt Generated
Interrupt Generated
TOK_DNE
TOK_DNE
TOK_DNE