Freescale Semiconductor MCF52277 Reference Manual page 411

Field
11–10 Multiplier Override. This field can possibly transmit-ISOs ( ISO-IN) to override the multiplier in the QH. This field
MultO must be 0 for all packet types not transmit-ISO.
For example, if QH.MULT equals 3; Maximum packet size equals 8; Total Bytes equals 15; MultiO equals 0
[default], then three packets are sent: {Data2(8); Data1(7); Data0(0)}.
If QH.MULT equals 3; Maximum packet size equals 8; Total Bytes equals 15; MultO equals 2, then two packets
are sent: {Data1(8); Data0(7)}
For maximal efficiency, software must compute MultO equals greatest integer of (Total Bytes / Max. Packet Size)
except for the case when Total Bytes equals 0; then MultO must be 1.
Note: Non-ISO and Non-TX endpoints must set MultO equals 00.
9–8 Reserved. Reserved for future use and must be cleared.
7–0 Status. Device controller communicates individual command execution states back to the DCD software. This field
Status contains the status of the last transaction performed on this dTD. The bit encodings are:
Bit
7
6
5
4
3
2–0
20.5.2.2.3 dTD Buffer Page Pointer List (Offset = 0x8–0x18)
The last five longwords of a device element transfer descriptor are an array of physical memory address
pointers. These pointers reference the individual pages of a data buffer.
Field
31–12 Buffer Pointer. Selects the page offset in memory for the packet buffer. Non virtual memory systems typically
Buffer Pointer set the buffer pointers to a series of incrementing integers.
0;11–0 Current Offset. Offset into the 4kB buffer where the packet begins.
Current Offset
1;10–0 Frame Number. Written by the device controller to indicate the frame number a packet finishes in. Typically
Frame Number correlates relative completion times of packets on an ISO endpoint.
Freescale Semiconductor
Table 20-47. dTD Token (continued)
Active. Set by software to enable the execution of transactions by the device controller.
Halted. Set by the device controller during status updates to indicate a serious error has
occurred at the device/endpoint addressed by this dTD. Any time a transaction results in the
halted bit being set, the active bit is also cleared.
Data Buffer Error. Set by the device controller during status update to indicate the device
controller is unable to maintain the reception of incoming data (overrun) or is unable to supply
data fast enough during transmission (under run).
Reserved.
Transaction Error. Set by the device controller during status update in case the device did not
receive a valid response from the host (time-out, CRC, bad PID).
Reserved.
Table 20-48. Buffer Page Pointer List
MCF52277 Reference Manual, Rev. 1
Universal Serial Bus Interface – On-The-Go Module
Description
Status Field Description
Description
20-53