Information

The USB-FS Controller uses the data stored in the BDs to determine:
• Who owns the buffer in system memory
• Data0 or Data1 PID
• Release Own upon packet completion
• No address increment (FIFO Mode)
• Data toggle synchronization enable
• How much data is to be transmitted or received
• Where the buffer resides in system memory
While the microprocessor uses the data stored in the BDs to determine:
• Who owns the buffer in system memory
• Data0 or Data1 PID
• The received TOKEN PID
• How much data was transmitted or received
• Where the buffer resides in system memory
The format for the BD is shown in the following figure.
Table 42-3. Buffer Descriptor Byte Format
31:26 25:16 15:8 7 6 5 4 3 2 1 0
RSVD
BC
(10 bits)
RSVD OWN DATA0/1
KEEP/
TOK_PID[3]
NINC/
TOK_PID[2]
DTS/
TOK_PID[1]
BDT_STALL/
TOK_PID[0]
0 0
Buffer Address (32-Bits)
Table 42-4. Buffer Descriptor Byte Fields
Field Description
31 –26
RSVD
Reserved
25 –16
BC[9:0]
The Byte Count bits represent the 10-bit Byte Count. The USB-FS SIE changes this field upon the
completion of a RX transfer with the byte count of the data received.
15 –8
RSVD
Reserved
Table continues on the next page...
Chapter 42 Universal Serial Bus OTG Controller (USBOTG)
K20 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc. 1053