Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 874

Universal Serial Bus (USB)
Offset Bit Name
0x00 6 CNF
(cont.)
7
8–9 PID
10–12 —
1
13 TO
14 UN
15 —
0x02 0–15 Data length
0x04 0–31 Tx data buffer
pointer
1
Written by the USB controller after it finishes sending the associated data buffer.
Data length (the second half word of a TxBD) is the number of octets the CP should send from this BD's
data buffer. It is never modified by the CP.
Tx buffer pointer (the third and fourth half words of a TxBD) always points to the first location of the
buffer in internal or external memory. The pointer may be even or odd.
31.12.3 USB Transmit Buffer Descriptor (TxBD) for Host
Data to be transmitted with the USB to the CP by is arranged in buffers referenced by the TxBD ring. The
first word of the TxBD contains status and control bits.
0 1
OFFSET + 0 R —
OFFSET + 2
OFFSET + 4
OFFSET + 6
1
Entries in boldface must be initialized by the user.
2
All fields should be prepared by the user before transmission.
31-26
Table 31-15. USB Function TxBD Fields (continued)
Transmit confirmation. Valid only when the L bit is set; otherwise it is ignored. Applies to
multi-frame enabled endpoints (USEP n [MF] = 1); see
Registers (USEP0–USEP3)."
0 Continue to load the transmit FIFO with the next packet. Several packets may be loaded
to the FIFO.
1 Last packet that is loaded to FIFO. No more packets will be loaded to FIFO after a
packet marked CNF, till it transmitted.
Reserved, should be cleared
Packet ID. This bit field is valid for the first BD of a packet; otherwise it is ignored.
0X Do not append PID to the data.
10 Transmit DATA0 PID before sending the data.
11 Transmit DATA1 PID before sending the data.
Reserved, should be cleared.
Time out. Indicates that the host failed to acknowledge the packet.
1
Underrun. Indicates that the USB encountered a transmitter underrun condition while
sending the buffer.
Reserved, should be cleared.
The data length is the number of octets that the CP should transmit from this BD's data
buffer. It is never modified by the CP. This value should normally be greater than zero.
The transmit buffer pointer, which always points to the first location of the associated data
buffer, may be even or odd.The buffer may reside in either internal or external memory.
2 3 4 5
W I L TC CNF LSP
TX DATA BUFFER POINTER
Figure 31-21. USB Transmit Buffer Descriptor (TxBD)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
6 7 8 9 10
PID —
DATA LENGTH
Section 31.11.3, "USB Endpoint
11 12 13 14 15
NAK STAL TO UN —
1,2
Freescale Semiconductor