Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 876

Universal Serial Bus (USB)
Offset Bit Name
1
0x00 11 NAK
(cont.)
1
12 STAL
1
13 TO
1
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.
31.13 USB CP Commands
The following transmit commands are issued to the CP command register (CPCR). The USB Host
Commands format is shown as follows:
0 1 2
RST USBCMD
Note: Bits 4-7 (OPCODE) are always 1101; bits 8-11 (CH_NUM) are always 0000. See
"CP Command Register (CPCR),"
31.13.1 STOP Tx Command (USBCMD=001)
This command disables the transmission of data on the selected endpoint. After issuing the command the
corresponding endpoint FIFO should be flushed. No further transmissions will take place until the Restart
Tx Command is issued.
31.13.2 RESTART Tx Command (USBCMD=010)
This command enables the transmission of data from the corresponding endpoint on the USB. This
command is expected by the USB controller after a STOP Tx Command, or after transmission error
(underrun or time-out).
31-28
Table 31-16. USB Host TxBD Fields (continued)
NAK received. Indicates that the endpoint has responded with a NAK handshake.
The packet was received error-free; however, the endpoint could not accept it.
STALL received. Indicates that the endpoint has responded with a STALL
handshake. The endpoint needs attention through the control pipe.
Time out. Indicates that the endpoint failed to acknowledge the packet.
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.
3 4 5 6
OPCODE
for more information on the CPCR.
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Description
7 8 9 10 11
CH_NUM
12 13 14 15
ENDPOINT — FLG
Section 18.6.3,
Freescale Semiconductor